Effects of urban development on herpetofauna: final report

              Effects of Urban Development on Herpetofauna
(Heritage Grant Number U02009)
FINAL REPORT
December 31, 2003
Matt Goode, Jeff Smith, Melissa Amarello, Kirk Setser, and Nancy Favour
Desert Southwest Cooperative Ecosystem Studies Unit
School of Renewable Natural Resources
University of Arizona
Tucson, AZ 85721
Submitted to the Arizona Game and Fish Department
Heritage Fund - Urban Wildlife Program
Recommended Citation
Goode, M., J. Smith, M. Amarello, K. Setser, and N. Favour. Effects of Urban Development on
Herpetofauna. Nongame and Endangered Wildlife Program Heritage Report. Arizona Game and
Fish Department, Phoenix, Arizona.
Disclaimer
The findings, opinions, and recommendations in this report are those of the investigators who have
received partial or full funding from the Arizona Game and Fish Department Heritage Fund. The
findings, opinions, and recommendations do not necessarily reflect those of the Arizona Game and
Fish Commission of the Department, or necessarily represent official Department policy or
management practice. For further information, please contact the Arizona Game and Fish
Department.
Effects of Urban Development on Herpetofauna – Goode et al. i
Table of Contents
INTRODUCTION...................................................................................................................................... 1
METHODS................................................................................................................................................. 3
Study Area...................................................................................................................................... 3
Study Design.................................................................................................................................. 5
Capture, Marking, and Handling ................................................................................................... 5
Time-Area Constrained Surveys (TACS) .................................................................................... 6
Mark-Recapture............................................................................................................................. 7
Road Cruising ................................................................................................................................ 7
Golf Path Surveys.......................................................................................................................... 8
Incidental Amphibian and Reptile Observations .......................................................................... 9
Morphology of Focal Species ........................................................................................................ 9
Demography of Focal Species ....................................................................................................... 9
Radiotelemetry.............................................................................................................................10
Spatial Ecology of Tiger Rattlesnakes.........................................................................................10
Potential Golf Course Effects.......................................................................................................10
Plot Characteristics .......................................................................................................................11
RESULTS AND DISCUSSION ..............................................................................................................12
Overall Observations and Search Effort......................................................................................12
Time-Area Constrained Surveys (TACS) ..................................................................................16
Mark-Recapture...........................................................................................................................19
Road Cruising ...............................................................................................................................26
Golf Path Surveys........................................................................................................................29
Morphology of Focal Species ......................................................................................................30
Demography of Focal Species .....................................................................................................31
Effects of Urban Development on Herpetofauna – Goode et al. ii
Spatial Ecology of Tiger Rattlesnakes.........................................................................................37
Potential Golf Course Effects.......................................................................................................50
Plot Characteristics .......................................................................................................................51
Landscape Changes Due to Urban Development .......................................................................54
RESEARCH AND MANAGEMENT RECOMMENDATIONS.........................................................56
Research Recommendations ........................................................................................................56
Management Recommendations..................................................................................................59
ACKNOWLEDGEMENTS....................................................................................................................60
LITERATURE CITED............................................................................................................................60
APPENDIX A...........................................................................................................................................62
Effects of Urban Development on Herpetofauna – Goode et al. iii
Tables
1. All species observed...........................................................................................................................12
2. Individuals observed during different activities.................................................................................13
3. Individuals encountered during TACS...............................................................................................16
4. Species richness, number of individuals, and evenness on interior plots.........................................17
5. Species richness, number of individuals, and evenness on margin plots .........................................18
6. Species richness, number of individuals, and evenness on control plots .........................................19
7. Summary of mark-recapture data for tree lizards and common side-blotched lizards ....................20
8. Abundance estimates of tree lizards...................................................................................................21
9. Abundance estimates of side-blotched lizards...................................................................................22
10. Body size by age class data for tree lizards........................................................................................24
11. Body size by age class data for side-blotched lizards........................................................................25
12. Toads found on different road surfaces..............................................................................................26
13. Reptiles found on different road surfaces...........................................................................................27
14. Processing data for all tiger rattlesnakes ............................................................................................30
15. Sex ratios and body size data for focal species..................................................................................31
16. Space-use and movement data for tiger rattlesnakes.........................................................................39
17. Active season space-use and movement data for tiger rattlesnakes..................................................40
18. Active season space-use and movement data for male tiger rattlesnakes ........................................41
19. Active season space-use and movement data for female tiger rattlesnakes .....................................41
Effects of Urban Development on Herpetofauna – Goode et al. iv
Figures
1. Map showing the location of the Stone Canyon study site ................................................................. 3
2. “Footprint” of the Stone Canyon development near Oro Valley, Arizona ....................................... 4
3. Completed houses and houses under construction at the Stone Canyon development ..................... 4
4. Toe-clipping scheme used during mark-recapture .............................................................................. 6
5. Time-area constrained search plots and mark-recapture plots............................................................ 7
6. Roads and golf cart paths...................................................................................................................... 8
7. Interior plot I-15 .................................................................................................................................11
8. Percent of individuals observed while conducting various research activities ................................15
9. Population estimates for side-blotched lizards...................................................................................23
10. Population estimates for tree lizards...................................................................................................23
11. Age class data for rattlesnakes............................................................................................................31
12. Age class data for three lizard species and tortoises..........................................................................32
13. Size class distribution of tiger rattlesnakes ........................................................................................33
14. Size class distribution of black-tailed rattlesnakes.............................................................................34
15. Size class distribution of western diamond-backed rattlesnakes ......................................................34
16. Size class distribution of Gila monsters .............................................................................................35
17. Size class distribution of desert tortoises............................................................................................36
18. Size class distribution of regal horned lizards....................................................................................36
19. Size class distribution of collared lizards ...........................................................................................37
20. Initial capture locations for tiger rattlesnakes ....................................................................................37
21. Tiger rattlesnakes found on roads and golf cart paths .......................................................................38
22. Radiotracking locations of tiger rattlesnakes .....................................................................................38
23. Rainfall by season ..............................................................................................................................42
24. Rainfall per month of the summer monsoon season .........................................................................42
Effects of Urban Development on Herpetofauna – Goode et al. v
25. Home ranges for tiger rattlesnakes .....................................................................................................43
26. Home ranges of two tiger rattlesnakes on developed lots.................................................................44
27. Home ranges of two tiger rattlesnakes near the future Ritz-Carlton Resort.....................................45
28. Tiger rattlesnake locations on golf course tee boxes .........................................................................45
29. Locations of tiger rattlesnake #199 ....................................................................................................46
30. Tiger rattlesnake overwintering sites..................................................................................................47
31. Home ranges, tracking locations, and overwintering sites of five tiger rattlesnakes .......................48
32. Individual tiger rattlesnake crossing the road ....................................................................................48
33. Active kernel home ranges of three tiger rattlesnakes.......................................................................49
34. Locations of a radiotelemetered tiger rattlesnake that was killed .....................................................50
35. Body condition index for tiger rattlesnakes on and away from the golf course...............................51
36. Locations of all toads observed ..........................................................................................................52
37. Relative abundance of Sonoran Desert toads.....................................................................................52
38. Relative abundance of red-spotted toads............................................................................................53
39. Mean area of all plots classified into three categories .......................................................................53
40. Series of four orthophotoquads taken from 1992 – 2002..................................................................54
Effects of Urban Development on Herpetofauna – Goode et al. 1
INTRODUCTION
Habitat destruction associated with urban development may be the greatest threat to Arizona’s
wildlife, amphibians and reptiles included. Arizona is the second fastest growing state, and Maricopa
and Pima counties are among the fastest growing counties in the United States (U.S. Census Bureau
2000). Phoenix and Tucson, the state’s two largest cities, are increasing by literally hundreds of
people per day. This incredible growth has lead to unprecedented sprawl, consuming pristine desert at
an estimated rate of approximately 25 km2 per year in Pima County alone (Huckleberry 2002).
Although the desert is being developed at an alarming rate, very little is known about how
urbanization affects wildlife. This is especially true for herpetofauna, a group that typically receives
less scientific and conservation attention than mammals and birds, which are considered more
charismatic by most people. When large areas are mass graded to make room for row after row of
tract homes, we can expect wildlife to be negatively affected. But what about so-called “green
developments” where attempts are made to retain as much of the natural character of the surrounding
desert as possible? How does wildlife respond to developments with relatively large amounts of open
space? At what housing density do we start to see more serious effects? Which species are better able
to coexist with humans? Answering these kinds of questions is difficult, partly because we simply
haven’t done the research. In reality, the scientific community is partly to blame. Well-designed
studies have rarely been conducted in spite of innumerable opportunities to do so. In fairness, it would
have been difficult to predict the accelerated pace at which habitat destruction due to urbanization has
occurred, especially over the last 3-4 decades.
Studying the effects of urban development on wildlife is very difficult. Developers have been
reluctant to work with scientists, because they think the scientists will turn up an endangered species,
costing them millions of dollars in environmental compliance. In turn, scientists that work with
developers risk being branded as pro-development by the environmental community. In addition,
managing the problem of sprawl is exceedingly complicated, because it is closely tied to economic
growth, which in turn is tied to population growth, setting up a vicious cycle. Determining the effects
of development on wildlife is also going to take a while, and many scientists avoid long-term research
for a variety of reasons, not the least of which is the pressure to publish, the need to obtain tenure, and
the responsibility of training graduate students.
Aside from these obstacles, there is an urgent need to learn more about the effects of urban
development on wildlife, so the effects can be mitigated in the future. The population problem is not
going away anytime soon, so the need to coexist with wildlife and wild places is of paramount
importance. In his new book, Win-Win Ecology, Rosenzweig (2003) contends that we will never be
able to set aside all the land we need to maintain Earth’s biodiversity, which leads him to make a plea
for decreasing the size of our footprint and learning to design our living space in such a manner as to
bring as many species along as possible. In reality, the question is whether or not we will decide that
the intrinsic value of wildlife (even less charismatic species such as toads and snakes) is worth more
than the extrinsic value of real estate. If we don’t, then we can expect the built environment to
increase at the expense of suitable habitat for wildlife. If biodiversity decreases as a result of urban
development, then we may sustain large-scale negative impacts to ecological systems. In fact, there is
evidence that this has already happened. For example, destructive flooding in the mid-western United
States has resulted from the conversion of wetlands to agricultural fields and industrial areas, which no
longer have the capacity to absorb flood waters. Ironically, the economy may suffer as well, because
the value of land is related to the amount of open space and other environmental amenities such as the
presence of wildlife.
Effects of Urban Development on Herpetofauna – Goode et al. 2
As with all wildlife species, one of the biggest threats to herpetofauana posed by urban development is
the loss of suitable habitat. Because amphibians and reptiles can be found in every biotic community
in Arizona, conversion of desert to urban areas represents a loss of habitat. Adding to the seriousness
of the situation is the fact that areas that are growing the fastest (e.g., Phoenix and Tucson) are both
located in the relatively species-rich Sonoran Desert. As these cities spread across the desert, they
replace natural areas that are critical to the future of amphibians and reptiles in the state.
In this report, we present the results of a two-year study designed to investigate the effects of
development on herpetofauna at the single species, population, and community levels. Our goal was
to conduct a before-after-control-impact (BACI) study that would allow us to compare pre- and post-development
data at sites scheduled for development with sites that will remain undeveloped. We
worked closely with the developer and had access to detailed development plans. However, as is
often the case, development plans changed, and we were generally unable to obtain post-development
data.
Another factor that made it difficult for us to examine the direct effects of development was the fact
that the developer would not allow us to place our plots directly on lots that were going to be
developed. However, this is probably the only realistic way to conduct this type of research, because
the lots will eventually be sold, and landowners are unlikely to allow researchers on their property to
gather post-development data. However, we were able to place our plots in common areas throughout
the development, and immediately adjacent to lots along the margin of the development.
Despite these difficulties, we have laid the groundwork for what we feel will be a model study of the
effects of urban development on herpetofauna, and this report outlines our efforts. Stone Canyon is
typical of upscale developments in the region in that it consists of relatively low housing densities,
large and expensive homes, and is associated with a desert style golf course all within a gated
community. Residents are typically wealthy retirees who make their second homes in the desert
during the winter months. Therefore, Stone Canyon is probably fairly representative of what many
people may consider to be a relatively “low-impact” development. Stone Canyon is also being built at
the urban fringe, and is adjacent to a large protected area (Tortolita Mountain Park – Pima County).
This is typical of many developments in the area in that they too are positioned between higher density
developments closer to the urban core, and protected areas on public lands (e.g., Coronado National
Forest and Saguaro National Park).
We are currently continuing to conduct research at the site. One project, funded by the Arizona Game
and Fish Department, is focused on the effects of the golf course (at Stone Canyon and elsewhere in
the Tucson Basin) on herpetofauna. In addition, we are resurveying rock outcrops that we surveyed
several years ago when the site was still pristine desert as part of yet another AGFD-funded study.
We are currently requesting funding from the Arizona Water Sustainability Program to expand our
research at Stone Canyon to include an examination of how the enormous influx of water from the
golf course and increased population may affect herpetofauna, especially toads. And we plan to seek
funding from the United States Golf Association to more closely examine some of the mechanisms
that may lead to changes in the herpetofauna in and around Stone Canyon. We feel that the effects of
the development are likely going to occur over the long term. The fact that we began work in the
early stages of the development, has enabled us to set the stage for a long-term investigation of the
effects of urbanization on herpetofauna at a variety of levels.
Effects of Urban Development on Herpetofauna – Goode et al. 3
METHODS
Study Area
The study area is located at the Stone Canyon development site in the Tortolita Mountains, within the
town of Oro Valley on the northwest side of Tucson, Arizona (Figure 1). A large portion of the area is
characterized by relatively flat alluvial terrain interspersed with numerous isolated rock outcrops of
various sizes. The northern part of the area is comprised mainly of steep, rocky slopes consisting of
large boulders and exposed bedrock. Vegetation is typical of Sonoran Desertscrub, Arizona Upland
Subdivision (Turner & Brown 1982). Common plants include saguaro (Carnegia gigantea), triangle-leaf
bursage (Ambrosia deltoidea), foothill palo verde (Cercidium microphyllum), brittlebush (Encelia
farinosa), prickly pear and cholla (Opuntia spp.), barrel cactus (Ferrocactus wislizenii), and velvet
mesquite (Prosopis velutina). Elevation at the study site ranges from approximately 900 – 1100 m
(2,940 – 3,700 ft).
Figure 1. Map showing the location of the Stone Canyon study site north of Tucson, Arizona,
near the town of Oro Valley at the base of the Tortolita Mountains.
Stone Canyon is a large, up-scale development, which when completed will consist of a resort, golf
course, hiking and biking trails, and over 450 residential estates situated on one to five acre lots
(Figure 2). Currently, the golf course, clubhouse, and about 45 homes are either under construction or
completed. The area of the development where we are conducting most of our research is less
developed with only 11 houses under construction and 14 completed (Figure 3). Only a small number
of the completed homes are occupied; the others are for sale. The houses that are occupied are only
Effects of Urban Development on Herpetofauna – Goode et al. 4
Figure 2. Aerial photograph showing the “footprint” of the Stone Canyon development near
Oro Valley, Arizona.
Figure 3. Orthophotoquad of the Stone Canyon development near Oro Valley, Arizona,
showing lots with completed houses (orange) and houses under construction (green). Only the
initial phase of the development, including the Ritz-Carlton Hotel site (far right), is depicted.
Effects of Urban Development on Herpetofauna – Goode et al. 5
being used during the winter months, and the golf course is virtually empty during the summer, as
only residents of the development are permitted on the course. Stone Canyon is an exclusive
development with lots and houses that cost up to several millions dollars each. Although difficult to
predict based on a variety of mostly economic factors, the developers expect the entire development to
take ten years or greater.
Study Design
In general, our goal was to compare pre- and post-development data from sites that will be developed
to sites that will remain in their natural condition. When it became apparent that the site where we
originally planned to conduct our research (Rocking K Ranch) was not going to be developed in the
timeframe needed to conduct the study, we decided to change study sites. Unlike the original site,
some development had already occurred at the new site. Although not an ideal situation, we felt that
changing sites was critical if we were to obtain any post-development data. As it turns out, the
process of developing a site often takes many years, making it difficult to conduct a true before-after
study in a two year time frame. Furthermore, developers often change their plans, particularly when it
comes to the timing of construction. Although the golf course and clubhouse were already in place,
we began our research at the earliest stages of the residential development. In reality, impacts to the
site when we began were minor relative to what they will be when the development is completed.
Therefore, we are confident that the data we gathered will provide a good baseline to which to
compare.
We gathered data on a variety of single species, population, and community level parameters
pertaining to the herpetofauna of the area. In this section, we describe our general methods, and
specific techniques used to obtain data on each parameter we measured.
Capture, Marking, and Handling
Snakes. We captured all non-venomous snakes by hand and all venomous snakes (except coral
snakes, Micruroides euryxanthus) with 24” snake tongs (Whitney, Inc). We transported snakes in
cloth bags to our lab for processing (e.g., measuring, sexing, palpating). We permanently marked
each snake by injecting a passive integrated transponder (PIT tag) under the skin. These tiny
electronic devices are about the size of a grain of rice. We identified individuals by passing a PIT tag
reader (Destron-Fearing Co.), which displays a 10-digit alphanumeric code, over the snake’s body.
For rattlesnakes, we coded digits 0-9 with different paint colors, which were then used to paint the first
three proximal rattle segments of the rattle based on a unique three digit number assigned to each
snake based on the order in which snakes were captured. This gave each snake a unique rattle paint
code, making it unnecessary to recapture snakes observed in the field if the paint colors were visible.
In some cases, when snakes were recaptured for growth measurements or to replace their
radiotelemeter, we repainted the rattle again if necessary. In general, paint marks were resilient;
however, over time they will either wear off or the rattle segments containing the paint mark will
break off. Therefore, painted rattles segments are not considered permanent. The paint mark also
allowed us to quantify the number of times a rattlesnake shed its skin.
We anesthetized most rattlesnakes for processing in order to obtain accurate snout-vent lengths and to
facilitate assessment of reproductive condition via palpation. We used plastic tubes (JB Specialties,
Inc.), a hook (Rattlesnake Museum, Albuquerque, NM), and in some cases a “squeezebox” (a wooden
box lined with foam padding) to safely handle rattlesnakes during capture and processing. Our
experience handling venomous snakes minimized risk to both the snakes and ourselves. Snakes were
Effects of Urban Development on Herpetofauna – Goode et al. 6
released at their exact point of capture within 2-48 hours, depending on whether or not they were
chosen for a radiotelemeter implant.
Lizards. We captured lizards by hand or with nooses constructed with fishing poles and fly line
backing. When necessary, we transported lizards in cloth bags to our lab for processing. We
permanently marked Gila monsters (Heloderma suspectum) by injecting a PIT tag under the skin
immediately anterior to the pelvic girdle. All other species were permanently marked by toe clipping
(Medica, et al. 1971; see Figure 4) and temporarily marked by painting either a number (lizards
included in our mark-recapture study) or symbol on the skin that typically persists until the animal
sheds. Lizards were released within 1-48 hours, depending on whether or not they were brought back
to the lab for processing.
Figure 4. Diagram showing toe-clipping scheme used to
individually mark lizards captured during mark-recapture
sampling. It is not necessary to clip more than
one toe per appendage using this method (after Medica, P.
A., G. A. Hoddenback, and J. R. Lannom, Jr. 1971).
Tortoises. We captured tortoises (Gopherus agassizii) by
hand and processed them in the field. We followed the
protocol established by the Arizona Interagency Desert
Tortoise Team (Averill-Murray 2000). We marked tortoises
by notching with a triangular file and released them within a
half-hour. We also assessed the health of tortoises, paying
particular attention to the presence of symptoms associated
with upper respiratory tract disease (URTD).
Toads. We did not capture any toads during the course of this study other than a few individuals of
each species in order to photograph them to document their presence at the study site. However, we
did conduct extensive surveys for toads and toad breeding sites, both in and away from the actual
development site.
Time-Area Constrained Surveys (TACS)
We conducted time-area constrained searches (TACS) on 48 circular, 1-ha plots (Figure 5). We
placed 16 plots within the development (Interior), 16 plots along the outer perimeter of lots (Margin),
and 16 plots outside the development (Control). We randomly located “control” plots no less than 1
km from the development in an area that will become Tortolita Mountain Preserve, a county park that
will protected from development for the foreseeable future. We surveyed plots three times each
during the summer rainy seasons (July – September) of both 2002 and 2003. Each day we conducted
TACS, three people surveyed three plots each as predetermined by our random sampling schedule.
We searched each plot for one hour using a variety of search techniques, including actively looking
for animals while walking slowly, scanning with binoculars, using mirrors to shine sunlight into
crevices in search of hiding reptiles, and listening for reptiles moving in vegetation. We recorded
UTM coordinates for each individual encountered. We also recorded a variety of environmental data
before and after each survey, and we did not conduct surveys on days with anomalous weather
conditions, such as overcast skies. Although we did not conduct trials in an attempt to detect observer
biases, we did provide extensive training in survey methodology to all personnel.
Effects of Urban Development on Herpetofauna – Goode et al. 7
Mark-Recapture
We randomly selected a subset of 6 TACS plots, two from each plot category (i.e., interior, margin,
and control), on which to conduct mark-recapture efforts. In 2002 and 2003, during the months of
July, August, and September, we conducted mark-recapture on each plot for five consecutive days.
We captured all tree lizards (Urosaurus ornatus) and side-blotched lizards (Uta stansburiana), and for
each individual we recorded UTMs, sex, age class, snout-vent length (SVL), and mass. We toe
clipped and painted a number on each lizard according to our protocol (see above) and released each
lizard at its exact point of capture. It usually took about 5 minutes to handle a lizard. When we
resighted or recaptured marked individuals, we recorded their location, and if a month had passed, we
recaptured (if they were resightings) and processed them again. We used Program MARK to estimate
population size. We recorded a variety of environmental data before and after each survey, and we
did not conduct surveys on days with anomalous weather conditions, which happened only once
during the course of the study. As with TACS, we did not conduct trials in an attempt to detect
observer biases; although, we did provide extensive training in survey methodology to all personnel in
an effort to minimize variation in our data due to differences in observer abilities.
Road Cruising
We spent a significant amount of time at night driving paved and dirt roads throughout the
development (Figure 6). Road cruising was very productive at the site, and nearly every animal
observed on the road was alive, because the development is within a gated community with restricted
access, and we were usually the only people present at night. The main road through Stone Canyon is
Figure 5. Aerial photograph of the Stone Canyon development site near Oro Valley, Arizona,
showing 48 time-area constrained search plots (TACS) and 6 mark-recapture plots (denoted by
a half-black circle).
Effects of Urban Development on Herpetofauna – Goode et al. 8
approximately six miles in length, winding through various stages of development. The road begins at
the gate house and is surrounded by several lots that contain houses, some of which are occupied and
have been recently landscaped. Although we recorded amphibians and reptiles observed on the road
in this area, we did not conduct intensive research (e.g., mark-recapture sampling, TACS) there. In
addition to the main road, we surveyed the paved side roads leading into current and future residential
areas. We also surveyed the dirt road that passes through the area that will be developed during the
last phase of construction.
Golf Path Surveys
We conducted numerous golf path surveys using a golf cart supplied by the Stone Canyon Golf Club.
On the majority of nights during the summer monsoon season in 2003, at least one person cruised the
golf cart path that winds through the golf course (Figure 6), traversing a variety of terrain throughout
the development site. We were successful at finding a variety of amphibian and reptile species during
golf path surveys. We found that cruising golf paths was an excellent way to see smaller animals that
may be missed during road cruising surveys using an automobile. We cruised the entire 18-hole cart
path at least once per survey night, recording the locations of all amphibians and reptiles found. We
also recorded other data, including distance to nearest golf course turf, temperature, and humidity. In
addition, we conducted toad surveys at water features (ponds) along the golf path.
Figure 6. Aerial photograph showing roads and golf cart paths surveyed at the Stone Canyon
study site near Oro Valley, Arizona, from 2002-2003. Paved roads (red), dirt roads (light blue),
and the golf cart path (yellow) were surveyed using automobiles and golf carts.
Effects of Urban Development on Herpetofauna – Goode et al. 9
Incidental Amphibian and Reptile Observations
We recorded all snakes and tortoises, and all lizards of certain focal species, observed while
conducting our research (e.g., during radiotelemetry sessions) and walking to and from our vehicles in
2002 and 2003. Each time an animal was observed we recorded the date, time, species, and location.
We were unable to calculate the number of individuals observed per unit effort for incidental
observations, because we did not keep track of time while conducting the above activities. However,
incidental observations are important and may contribute to the overall species list for a given study.
Morphology of Focal Species
Snakes. We recorded SVL, tail length, and mass for all snakes captured. In addition, we recorded
head width and length and rattle segment widths on tiger rattlesnakes (Crotalus tigris) and black-tailed
rattlesnakes (Crotalus molossus). We measured SVL on non-venomous species by stretching them
out along a measuring tape, and we either used a squeezebox or anesthetized rattlesnakes. When
using the squeezebox, we traced the total length of the snake (minus the rattle) twice on the plexiglass
cover of the squeezebox. We measured the trace twice to help insure accuracy. If measurements
differed by greater than 1% of the total length, then we measured again until we obtained two
measurements that were within 1% of each other. We also traced the outline of the head to get length
and width measurements. We tubed rattlesnakes in order to measure tail length, which we subtracted
from the total length to arrive at SVL. We weighed snakes in a cloth bag and then subtracted the mass
of the empty bag to determine the mass of the snake. Digital calipers were used for head and rattle
measurements while snakes were anesthetized.
Lizards. We recorded SVL, tail length, and mass for all lizards captured. In addition, we recorded
head width and length for collared lizards (Crotaphytus collaris), regal horned lizards (Phrynosoma
solare), and Gila monsters. We measured SVL and tail length using a measuring tape or ruler, and we
weighed lizards by the same method as snakes.
Tortoises. For tortoises, the only morphological data we recorded was midline carapace length
(MCL) using pottery calipers and a measuring tape.
Toads. We did not capture, and therefore process, any toads during the course of the study.
Demography of Focal Species
Our demography data are confined to focal species (generally those species for which we obtained
relatively large sample sizes), not all species observed. We sexed all animals captured (if possible)
and classified each into one of three age classes: adult, juvenile, or neonate/hatchling. For a female to
be classified as an adult, it had to exceed the minimum size at which gravid individuals have been
found for the species (Gila monsters, Goldberg & Lowe 1997; tortoises, Averill-Murray 2002; black-tailed
rattlesnakes, Goldberg 1999a; tiger rattlesnakes, Goldberg 1999b; western diamond-backed
rattlesnakes [Crotalus atrox], Rosen & Goldberg 2002, Jacob, et al. 1987; regal horned lizards,
Howard 1974; collared lizards, Ballinger & Hipp 1985, Parker 1973). For a male to be classified as
an adult, it had to exceed the minimum size at which males have been found to be reproductively
mature (see above citations). We distinguished neonates from juveniles based on their small size and
at what time of the year they were observed. For snakes and tortoises, we designated all animals born
this year as neonates; for lizards, some individuals that hatched earlier in the year approached adult
size, so we based age class specification on body size. Rattlesnakes were categorized by the presence
Effects of Urban Development on Herpetofauna – Goode et al. 10
of a rattle consisting of only one segment (the button), indicating that the snake had shed only once,
approximately one week after birth, and was therefore a neonate.
Radiotelemetry
We surgically implanted temperature-sensing radiotelemeters (Holohil, Ltd., Model SR2) into 33 tiger
rattlesnakes. Due to premature battery failure, we were unable to track several snakes as long as
intended. A total of six tiger rattlesnakes with radiotelemeters died during the course of the study:
two were killed by construction workers, two were presumably killed by predators, one did not
recover from anesthesia following implant surgery, and one died in transported from the field to our
lab for transmitter replacement surgery (cause of death unknown). Despite these problems, we were
still able to follow several individuals for two field seasons, and we were able to obtain a large dataset
on numerous other individuals.
We only implanted snakes if the mass of the radiotelemeter (1.8 g, 5.2 g, or 9 g) was 5% or less of the
snake’s mass. This resulted in a minimum mass of 36 g to be eligible for an implant, although a snake
also had to be large enough in diameter (determined by visual inspection and based on experience) to
receive an implant. We anesthetized snakes using Isoflurane (Abbott Laboratories), an inhalant,
which is highly soluble in tissue and allows for precise and easily controllable dosing. Using a sterile
procedure (modified from Reinert & Cundall 1982), we implanted transmitters into the peritoneum
(i.e., gut cavity), with the antennae placed under the skin and stretched toward the head to increase the
range of signal detection. Several snakes received multiple implants. No snakes died or showed any
obvious ill effects of implantation.
Spatial Ecology of Tiger Rattlesnakes
We used a Garmin E-Map, Gecko 201, or Gecko 301 (Garmin, Inc.) global positioning system (GPS)
receiver to record locations. All GPS data were imported into ArcView (ESRI, Inc.) for display and
spatial analyses using the Animal Movement Analysis extension (obtained online from Alaska
Biological Science Center, USGS-Biological Resources Division). We used a variety of parameters
to characterize tiger rattlesnake movement patterns, including total distance moved, mean distance
moved per day, and whether or not the snake was moving when located. To characterize home
ranges, we estimated their size using the minimum convex polygon (MCP) technique and the active
kernel (AK) technique. We estimated core activity areas using the 50%, 25%, and 10% isopleths
generated by the AK technique. We examined differences in movement patterns and home range size
between active seasons in 2002 and 2003 when sample sizes permitted.
Potential Golf Course Effects
To investigate potential differences in tiger rattlesnakes found using the golf course with those found
away from the golf course, we compared an index of condition based on body size. This index is
calculated by dividing a snake’s mass by its SVL, giving the mass per unit body length. A healthy
snake will presumably be heavier per unit length than an unhealthy snake. We also compared
movement parameters of tiger rattlesnakes found using the development area with those found away
from the area (i.e., home range did not include the golf course), and with tiger rattlesnakes from
undeveloped areas that we studied previously (Goode & Wall 2002).
We also examined potential golf course effects on toads. We conducted toad surveys at two man-made
ponds (i.e., water hazards) along the golf course. In addition, we tallied all toads observed
Effects of Urban Development on Herpetofauna – Goode et al. 11
during golf path surveys and on several evenings when road cruising specifically for toads before and
during the summer rainy season. Finally, we conducted breeding site surveys on and off the golf
course on several rainy nights in July and August.
Plot Characteristics
We characterized each plot based on landscape features that we felt would reflect changes that may
result from development activities. We used high-resolution (six inches per pixel), georeferenced,
digital aerial orthophotoquads (available online from PAGNET, Pima County Planning Office) to
calculate the area of each plot into three categories: rock outcrop, desert scrub on relatively well
developed soil, and bare ground associated with anthropogenic disturbance. Using ArcView, we
traced the edges of rock outcrops and other features of interest producing a polygon for which an area
was calculated. We have provided an example of how we characterized plots (Figure 7). We
obtained percentages of each landscape type that we plan to compare with post-development data in
the future, allowing us to correlate any changes in herpetofauna with potential changes in habitat. We
characterized plots in the above manner, because we felt it was a more accurate and informative than
doing vegetation relevés, which we originally proposed to do. The availability of high-resolution
imagery allowed us to utilize analytical techniques that are normally unavailable for exurban areas
unless these areas are slated for development.
Figure 7. Close up view of interior plot I-15 at the Stone Canyon study site near Oro Valley,
Arizona, from 2002-2003 depicting the manner in which high-resolution digital aerial
photography was used to quantify the amount of rock outcrops (green), anthropogenic
disturbance (red), and remaining flat, open desertscrub.
Effects of Urban Development on Herpetofauna – Goode et al. 12
RESULTS AND DISCUSSION
Overall Observations and Search Effort
We observed a total of 6560 individual amphibians and reptiles belonging to 35 species (Table 1)
during the study, which lasted from July – October in 2002 and May – October in 2003.
Table 1. Total number of individuals of all species observed in increasing order at the Stone
Canyon study site near Oro Valley, Arizona from 2002-2003.
Common Name Scientific Name Number of Individuals
Ring-necked Snake Diadophis punctatus 1
Western Threadsnake Leptotyphlops humilis 1
Common Kingsnake Lampropeltis getula 2
Long-nosed Leopard Lizard Gambelia wislizenii 3
Sonoran Coralsnake Micruroides euryxanthus 3
Desert Spiny Lizard Sceloporus magister 5
Black-necked Gartersnake Thamnophis cyrtopsis 7
Long-nosed Snake Rhinocheilus lecontei 8
Nightsnake Hypsiglena torquata 8
Couch’s Spadefoot Scaphiopus couchi 8
Western Patch-nosed Snake Salvadora hexalepis 9
Banded Sandsnake Chilomeniscus cinctus 9
Smith’s Black-headed Snake Tantilla hobartsmithi 9
Western Lyresnake Trimorphodon biscutatus 12
Sonoran Spotted Whiptail Lizard Cnemidophorus sonorae 24
Gophersnake Pituophis catenifer 27
Gila Monster Heloderma suspectum 27
Coachwhip Masticophis flagellum 29
Zebra-tailed Lizard Callisaurus draconoides 37
Sonoran Whipsnake Masticophis bilineatus 43
Black-tailed Rattlesnake Crotalus molossus 43
Eastern Collared Lizard Crotaphytus collaris 47
Regal Horned Lizard Phrynosoma solare 48
Great Plains Toad Bufo cognatus 56
Western Diamond-backed Rattlesnake Crotalus atrox 63
Tiger Rattlesnake Crolatus tigris 84
Western Banded Gecko Coleonyx variegatus 112
Desert Tortoise Gopherus agassizi 133
Great Earless Lizard Cophosaurus texanus 151
Whiptail lizard Cnemidophorus spp. 183
Tiger Whiptail Lizard Cnemidophorus tigris 431
Clark’s Spiny Lizard Sceloporus clarki 553
Red-spotted Toad Bufo punctatus 624
Ornate Tree Lizard Urosaurus ornatus 771
Colorado River Toad Bufo alvarius 802
Common Side-blotched Lizard Uta stansburiana 2290
Total 6,629
In an effort to make the numbers of herpetofauna observed more meaningful, we kept track of the
time we spent conducting various activities, which allowed us to calculate the average number of
Effects of Urban Development on Herpetofauna – Goode et al. 13
person-hours required to observe an individual of each species group (Table 2). These figures do not
include incidental observations, because it was impractical to keep track of time spent while
conducting activities such as radiotracking and traveling to and from study plots. On average, we
observed an individual amphibian or reptile every 0.19 hours or slightly less than every 12 minutes.
Lizards were the most commonly observed species group (ca. one lizard observed every 16 minutes),
followed by toads (ca. one toad observed every 42 minutes), snakes (ca. one snake observed every 5
hours and 53 minutes), and tortoises (ca. one every 34 hours). However, these numbers are
misleading, because the likelihood of finding different species varies by observer activity. For
example, tortoises are not found at night while road cruising, but are found relatively frequently during
TACS (one tortoise observed every 8 hours and 14 minutes). Therefore, we report the average time
needed to observe an individual of each species group depending on the activity in which the observer
was engaged. The best method for observing toads was golf cart path surveys. The best method for
observing tortoises and lizards was TACS, and the best method for observing snakes was road-cruising
if effort is considered (Figure 8). These findings were not surprising to us, but we stress that
they are important to consider when designing herpetological research, because individuals observed
per unit effort can be used as an index of relative abundance that can be compared across treatments,
taxa, or studies. Below, we break down our observations by species group.
Table 2. Total number of individuals by species group observed during different observer
activities at the Stone Canyon Study site near Oro Valley, Arizona, from 2002-2003. H/I =
hours required to observe one individual. Number in parentheses is total person-hours spent
per method. Individuals observed incidentally are not included.
Snakes. We observed a total of 364 snakes (including incidental observations) of 17 species during
the study, 241 of which we captured and processed (we processed all snakes captured). We were
unable to catch numerous snakes, mainly coachwhips (Masticophis flagellum) and whipsnakes
(Masticophis bilineatus), which explains why the total number of snakes observed does not match
with the figure reported in Table 2.
Our large dataset pertaining to snakes is significant for several reasons. Snakes can be difficult to
study, because they are inactive for large periods of time, and when active tend to be secretive, and
therefore infrequently observed. Snakes are apparently relatively abundant at our study site, and
because the roads are off-limits to the general public, we have an ideal situation for finding snakes. It
will be interesting to look at relative abundance and community composition of the snake fauna as the
development continues. We predict that road kills will increase dramatically as more and more people
come to live in the development and traffic increases as a consequence. However, most people who
will come to live at Stone Canyon will be winter residents, which may lead to lower road mortality,
because snakes will be generally inactive when human use is at its peak.
TACS Mark-Recapture Road-cruising Golf Path Surveys Total
Species
Group N
H/I
(288) N
H/I
(565.3) N
H/I
(148.5) N
H/I
(186.6) N
H/I
(1188.3)
Snakes 23 12.52 0 0.00 84 1.77 95 1.96 202 5.88
Lizards 2512 0.11 1950 0.29 43 3.45 138 1.35 4643 0.26
Tortoises 35 8.23 0 0.00 0 0.00 0 0.00 35 33.95
Toads 18 16.00 0 0.00 134 1.11 1338 0.14 1490 0.80
Total 2588 0.11 1950 0.29 261 0.67 1571 0.10 6370 0.19
Effects of Urban Development on Herpetofauna – Goode et al. 14
Our snake data are also important, because snakes tend to be long-lived, especially heavy-bodied,
relatively sedentary pit vipers such as rattlesnakes, for which we have the most data. Because the
effects of the development are likely to be long-term, focusing on long-lived animals to investigate the
effects makes sense. The problem with snakes is that recaptures tend to be uncommon; however, we
are optimistic that we will eventually recapture enough individuals to provide for meaningful results,
because we have marked such a large number of animals.
Lizards. We observed a total of 4813 lizards (including incidental observations) of 13 species during
the study, 1008 of which we captured, and 939 of which we processed. We did not capture every
lizard encountered, but we did capture all Gila monsters, horned lizards, and collared lizards, and we
captured all side-blotched lizards and tree lizards on mark-recapture plots if possible (see below).
The large dataset we obtained on lizards puts us in position to make meaningful comparisons related
to single species, population, and community level parameters as the development continues. In
particular, the large amount of data we obtained on tree lizards and side-blotched lizards during mark-recapture
efforts will enable us to compare population estimates before and after development (see
Mark-Recapture section below for details). Data from TACS surveys will enable us to compare
community level parameters, and data obtained from focal species (i.e., Gila monsters, collared
lizards, and regal horned lizards) will also be interesting to compare to post-development data,
especially relative abundance, distribution, and demography.
Tortoises. We observed a total of 184 tortoises during the study, 153 of which we captured, and 122
of which we processed in the field with minimal disturbance to the animal. We were unable to
process numerous tortoises, because it was impractical to carry our processing equipment with us at
all times.
The large number of tortoises at our study site is probably not a surprise given the fact that an
abundance of large boulders on relatively well-developed soils is a common feature of the area.
However, we think it would be a good idea to conduct more in-depth studies of tortoises in an attempt
to determine any effects the development may have on them. Arizona Game and Fish Department has
an active tortoise research and monitoring program; perhaps the Department could take a more active
role in studying tortoises at the site where they are extremely abundant and may be subject to
substantial threats as the development continues to grow. In a related study (also funded by AGFD),
we are in the process of developing interpretive signs that will be placed on the golf course. One of
these signs will feature the desert tortoise. We feel that a more intensive educational campaign is
warranted and that people living in the area would likely refrain from capturing tortoises to keep as
pets if just provided with the proper information.
Another way in which the development may negatively affect tortoises is the potential for increased
prevalence of disease, in particular, URTD. Biologists have hypothesized that the incidence of URTD
may increase as distance to urban areas decreases. We assessed all tortoises captured during the study
for health based on AGFD protocols. We only observed 1 individual with symptoms of URTD. As
the development grows, eventually reaching its maximum size of approximately 350 homes, it will be
important to continue to monitor tortoise health. We have discussed our findings with AGFD
scientists and Cristina Jones, University of Arizona graduate student conducting an AFGD-funded
study of URTD in urban and exurban tortoises. We will be happy to collaborate with these
researchers in the future if they feel that the data we are gathering are useful to them.
Effects of Urban Development on Herpetofauna – Goode et al. 15
Toads. We observed 1490 toads (not including incidental observations), none of which we captured
or processed. In reality, the number of toads observed was much higher, but we did not count every
toad encountered during road cruising, because there were nights during the breeding season that there
were so many toads on the road that counting them all and identifying each individual to species
would have been impractical. The toads observed include all those found while conducting TACS
(only 18 individuals), golf cart surveys, surveys of two artificial ponds on the golf course that act as
water hazards, and surveys of breeding sites throughout the development. Only those toads found
during 14 nights while specifically road cruising for toads are included in the total. These road
cruising efforts were designed to be repeated in the future for purposes of pre- and post-development
comparisons.
In retrospect, we feel that putting more effort into toad surveys would have been advisable. Toads are
extremely abundant at the site, especially during the summer rainy season, making it relatively easy to
obtain large sample sizes. In addition, toads may be a good species to monitor when examining
potential effects of urban development, because they are dependent on water sources that tend to
increase with human presence, and be available at times of the year when they are not normally
available in natural settings. In turn, these water sources are closely tied to reproduction, the ultimate
life history parameter for predicting the effects of anthropogenic disturbance. However, toads can be
difficult to monitor, because populations tend to fluctuate greatly from year to year, and in some years
significant reproduction may not occur depending on rainfall events.
Species by Method
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Snakes Lizards Tortoises Toads
Species
% per Method
GPS
RC
M-R
TACS
Figure 8. Percent of individuals by species group observed at the Stone Canyon study site near
Oro Valley, Arizona, from 2002-2003 while conducting various research activities. GPS = golf
path survey, RC = road cruising, M-R = mark-recapture, and TACS = time-area constrained
search. Although more snakes were found during golf path surveys, more per unit effort were
found while road cruising.
Effects of Urban Development on Herpetofauna – Goode et al. 16
Time-Area Constrained Surveys (TACS)
We observed 2588 individuals of 21 species during TACS (Table 3). The greatest number of species
observed on any plot during a one-hour survey period was 10, and the lowest number was 3.
Table 3. Numbers of individuals and individuals per hour in increasing order of all reptile and
amphibian species encountered during TACS at the Stone Canyon study site near Oro Valley,
Arizona, from 2002-2003.
Species Number of Individuals Hours/Individuals
Lampropeltis getula 1 288.00
Masticophis flagellum 1 288.00
Salvadora hexalepsis 1 288.00
Crotalus atrox 2 144.00
Gambelia wizlenii 2 144.00
Crotalus tigris 3 96.00
Sceloporus magister 4 72.00
Crotalus molossus 5 57.60
Phrynosoma solare 9 32.00
Masticophis bilineatus 10 28.80
Bufo punctatus 18 16.00
Cnemidophorus spp. 24 12.00
Crotaphytus collaris 24 12.00
Callisaurus draconoides 34 8.47
Gopherus agassizii 35 8.23
Cophosaurus texanus 148 1.95
Cnemidophorus sonorae 183 1.57
Urosaurus ornatus 364 0.79
Sceloporus clarki 382 0.75
Cnemidophorus tigris 431 0.67
Uta stansburiana 907 0.32
Total 2588 0.17
To facilitate post-development comparisons, we present TACS data on species richness and evenness
for the three plot types (Tables 4, 5, and 6) by year and for both years combined. Overall, we
observed more amphibian and reptile species and individuals on control plots than either interior or
margin plots. There were only slight differences in evenness between and among plots or plot types,
within or between years.
Examination of between-year data indicated that both species richness (t = 3.54, df = 286, p < 0.0005)
and number of individuals (t = -2.02, df = 286, p < 0.04) were higher in 2003 compared to 2002 when
pooled. However, when we examined between-year data by time of year, there were no significant
differences in species richness (t = 0.57, df = 94, p > 0.570) or number of individuals (t = -0.16, df =
94, p > 0.875) in survey period one, significant differences in species richness (t = -4.88, df = 94, p <
0.0001) and number of individuals (t = -3.69, df = 94, p < 0.0004) in survey period two, and
significant differences in species richness (t = -2.13, df = 94, p < 0.036), but not number of individuals
(t = -0.06, df = 94, p > 0.950), in survey period three.
Effects of Urban Development on Herpetofauna – Goode et al. 17
We also made within-year comparisons of TACS data. In 2003, ANOVA results revealed that species
richness was significantly higher (F = 15.55; df = 2,41; p < 0.0001) during the first survey period
(July), and number of individuals was significantly lower (F = 8.65; df = 2, 41; p < 0.0003) during the
second survey period (August). In 2003, There were no differences in species richness (F = 0.02; df =
2, 141; p > 0.977) or number of individuals (F = 0.03; df = 2, 141; p > 0.970) among the three
sampling periods.
One-way ANOVA revealed no differences in species richness between plot types when data were
pooled across years (F = 1.10; df = 2, 285; p > 0.333), but there were significantly more individuals on
control plots than on interior or margin plots (F = 6.39; df = 2, 285; p < 0.002). Within-year results
revealed that there were no differences in species richness (F = 1.63; df = 2, 45; p > 0.207) or number
of individuals (F = 1.60; df = 2, 45; p > 0.213) among plot types in 2002. In 2003, there were
significantly more individuals on control plots than either interior or margin plots (F = 3.12; df = 2,
45; p < 0.05), but species richness did not differ (F = 0.37; df = 2, 45; p > 0.690).
Table 4. Species richness (SR), number of individuals (N), and evenness (E) for all
herpetofauna encountered during time-area constrained searches (TACS) on interior plots at
the Stone Canyon study site near Oro Valley, Arizona, from 2002-2003. SE = standard error.
Interior 2002 2003 Total
Plot # SR N E SR N E SR N
1 3 16 0.79 8 27 0.79 9 43
3 8 20 0.88 5 18 0.76 8 38
4 5 29 0.81 6 22 0.75 7 51
6 3 19 0.95 7 19 0.67 6 38
8 5 45 0.76 7 32 0.61 7 77
9 4 14 0.94 7 6 0.82 6 20
10 7 36 0.69 6 22 0.83 7 58
12 7 37 0.67 5 19 0.64 7 56
13 8 32 0.57 6 23 0.73 9 55
14 4 21 0.85 6 11 0.68 6 32
15 6 18 0.80 6 34 0.64 7 52
16 5 16 0.77 6 33 0.74 6 49
17 5 27 0.81 6 23 0.89 6 50
18 4 20 0.67 5 38 0.70 7 58
19 5 13 0.70 8 41 0.84 8 54
20 6 21 0.79 7 22 0.83 7 43
Mean
+
SE
5.3
+
0.4
24.0
+
2.3
0.78
+
0.03
6.3
+
0.2
24.4
+
2.4
0.70
+
0.03
7.1
+
0.2
48.4
+
3.2
At present, we are limited in our interpretations of the potential effects of development on the
amphibian and reptile community at the Stone Canyon study, because development did not occur as
we expected, preventing us from making significant before-after comparisons. However, we have
established an excellent baseline to which we can compare post-development TACS data in the future.
We have also examined differences in species richness, numbers of individuals, and evenness between
and within years, and among plot types. The most important point to make about diversity and
relative abundance of herpetofauna at the site is that it is highly variable and can change from month
to month, year to year, and across plot types. This provides us with a background to use as a
meaningful context within which to place post-development results. Regarding relative abundance,
Effects of Urban Development on Herpetofauna – Goode et al. 18
this natural variation is not surprising, given what we know about the fluctuating nature of amphibian
and reptile populations. However, species diversity is a much more stable parameter and may be
more appropriate for examining the effects of development on herpetofauna, because some species
fare well in urban settings while others do poorly. On the other hand, variation in relative abundance
may make it difficult to detect trends.
Interestingly, our “control” plots were generally more diverse and contained greater numbers of
reptiles (very few toads were observed during TACS) than either margin or interior plots. Because
very little development activity has occurred, differences in reptile diversity and relative abundance is
more likely due to differences in landscape structure among plot types. In general, control plots
contained less rock outcrops and more desertscrub (see Plot Characteristics section below). The
greater diversity in landscape structure on control plots probably contributed to increased diversity and
relative abundance of reptiles. In any case, plots will be compared to themselves and not to each other
in order to assess potential effects of development.
Table 5. Species richness (SR), number of individuals (N), and evenness (E) for all
herpetofauna encountered during time-area constrained searches (TACS) on margin plots at
the Stone Canyon study site near Oro Valley, Arizona, from 2002-2003. SE = standard error.
Margin 2002 2003 Total
Plot # SR N E SR N E SR N
2 6 17 0.82 5 13 0.76 6 30
3 7 23 0.80 8 31 0.68 9 54
4 5 20 0.78 8 36 0.67 7 56
5 5 14 0.71 5 18 0.87 5 32
6 6 17 0.77 8 14 0.88 7 31
7 4 11 0.76 8 15 0.94 8 26
10 4 15 0.88 4 18 0.78 4 33
11 4 10 0.92 5 18 0.74 5 28
13 6 32 0.72 7 28 0.84 7 60
14 7 42 0.83 6 58 0.78 7 100
15 9 35 0.74 8 40 0.76 8 75
16 8 39 0.64 9 32 0.83 9 71
17 5 12 0.79 7 37 0.58 7 49
19 8 32 0.73 10 45 0.66 9 77
20 6 16 0.80 5 34 0.73 6 50
21 7 15 0.89 4 9 0.92 7 24
Mean
+
SE
6.1
+
0.4
21.9
+
2.6
0.79
+
0.02
6.7
+
0.5
27.9
+
3.4
0.77
+
0.03
6.9
+
0.4
49.8
+
5.6
Besides varying by plot type, lizard relative abundance, diversity, and evenness varied from year to
year. It is important to understand this natural variation, because it will likely interact, or even mask,
potential variation caused by development. Year-to-year variation in herpetofaunal abundance is
common, especially in short-lived species such as the common diurnal lizard species that comprise the
bulk of our data. The more data we obtain on natural variation, the better we will be able to make
inferences about variation due to development. This can be accomplished by continuing to gather data
on control plots through time. In our case, because development has only just begun, many of our
margin plots are currently acting as control plots. As the development extends into the northeast part
of the study site, margin plots will become interior plots. However, because our control plots are on
land that will become a preserve, we can be relatively sure that they will continue to serve as control
Effects of Urban Development on Herpetofauna – Goode et al. 19
plots for decades to come. It is our sincere hope that we will continue to gather data at Stone Canyon
for many years to come. It seems likely that only through a long-term study such as that which we
envision, can we hope to truly understand the effects of the development on the herpetofauna residing
there.
Table 6. Species richness (SR), number of individuals (N), and evenness (E) for all
herpetofauna encountered during time-area constrained searches (TACS) on control plots at
the Stone Canyon study site near Oro Valley, Arizona, from 2002-2003. SE = standard error.
Control 2002 2003 Total
Plot # SR N E SR N E SR N
1 5 9 0.91 5 29 0.79 6 38
2 8 17 0.61 5 17 0.60 8 34
3 6 23 0.80 6 27 0.76 7 50
4 5 17 0.78 8 16 0.86 9 33
7 6 33 0.70 6 21 0.81 7 54
8 6 40 0.70 7 42 0.73 7 82
9 6 50 0.73 7 43 0.72 7 93
10 7 56 0.77 5 44 0.73 6 100
11 8 26 0.85 6 22 0.78 8 48
12 4 21 0.82 5 47 0.49 6 68
13 7 47 0.65 8 59 0.70 8 106
14 5 19 0.68 9 80 0.50 8 99
17 4 24 0.72 8 36 0.63 8 60
18 8 27 0.63 7 49 0.64 7 76
19 8 38 0.73 7 31 0.66 9 69
21 6 16 0.90 8 18 0.89 7 34
Mean
+
SE
6.2
+
0.3
28.9
+
3.4
0.75
+
0.02
6.7
+
0.3
36.3
+
4.4
0.70
+
0.03
7.4
+
0.2
65.3
+
6.3
Mark-Recapture
We observed a total of 1950 lizards during mark-recapture sampling (Table 2). Of the total lizards
observed, we captured 587 and recaptured or resighted 424. We captured 173 and recaptured or
resighted 132 tree lizards (76.3%), and we captured 414 and recaptured or resighted 292 side-blotched
lizards (70.5%) (Table 7). Sex ratios of captured lizards of both species were heavily skewed towards
males, especially for side-blotched lizards. Control plots had fewer tree lizards than both interior and
margin plots, and side-blotched lizards were least abundant on margin plots. Tree lizards were most
abundant on margin plots, and side-blotched lizards were most abundant on interior plots. We had
slightly better success recapturing tree lizards than side-blotched lizards. The similarity in recapture
success between species is misleading, because most lizards we observed but were unable to capture
were hatchling and juvenile side-blotched lizards.
We attempted to estimate population sizes of tree lizards (Table 8) and side-blotched lizards (Table 9)
using Program MARK. In several cases, the program was unable to produce an estimate, presumably
because our recapture rates were too low. The largest population size estimate in any one five-day
sampling period was 180 side-blotched lizards on control plot 8 in August of 2003, and the smallest
estimate was four tree lizards, which occurred on four occasions.
Effects of Urban Development on Herpetofauna – Goode et al. 20
Table 7. Summary of mark-recapture data for tree lizards (Urosaurus ornatus) and common
side-blotched lizards (Uta stansburiana) at the Stone Canyon study site near Oro Valley,
Arizona from 2002-2003.
Urosaurus ornatus Uta stansburiana
Plot Type
and
Number
Total Days
Surveyed
Number
Marked
Number
Resights
Sex
Ratio
(F:M)
Number
Marked
Number
Resights
Sex
Ratio
(F:M)
Control
8 31 32 14 10:14 74 43 13:19
11 29 17 12 4:6 63 49 8:23
Interior
15 30 23 27 6:14 82 48 11:22
18 30 35 34 13:13 100 88 10:34
Margin
4 29 30 27 9:14 36 19 3:12
15 30 36 18 16:17 59 45 7:21
Total 179 173 132 58:78 414 292 52:131
Population size estimates varied greatly from month to month and from year to year for both species.
However, a few general trends were evident. Population estimates tended to increase in size later in
the summer rainy season in August and September, especially for side-blotched lizards (Figures 9 and
10). This increase may be partially explained by a substantial increase in precipitation in August in
both 2002 and 2003.
Whatever the reasons for fluctuating population sizes, caution must be used when comparing pre- and
post-development estimates of absolute abundance to examine potential effects of development.
Comparisons are difficult primarily because confidence intervals associated with population size
estimates tend to be large, making it difficult to tease out differences. However, analytical approaches
have been developed that allow for comparisons of trends rather than point estimates. It seems
reasonable to assume that when trends are echoed across plots, then the trends probably reflect reality.
We are currently exploring a variety of methods for analyzing lizard population estimates, and we are
confident that a satisfactory approach will be developed to compare post-development estimates with
our baseline results. In addition, we plan to expand our analyses from a series of estimates for each
sampling period, to overall yearly estimates. As with TACS data, our baseline data indicate that there
is a great deal of variation in population sizes between and within years and within and among plot
types. Understanding this natural variation is essential if we are to make sense of potential changes in
population size related to development.
Effects of Urban Development on Herpetofauna – Goode et al. 21
Table 8. Abundance estimates of tree lizards (Urosaurus ornatus) on six mark-recapture plots
at the Stone Canyon study site near Oro Valley, Arizona, in 2002 and 2003. LCI = lower
confidence interval, UCI = upper confidence interval.
Plot Month Year Abundance LCI UCI
Control 8 July 2002 16 9 52
August 2002 * * *
September 2002 * * *
July 2003 4 4 15
August 2003 17 12 37
September 2003 6 4 25
Control 11 July 2002 7 4 33
August 2002 5 3 22
September 2002 4 2 30
July 2003 29 10 153
August 2003 7 5 21
September 2003 19 6 117
Interior 15 July 2002 6 5 16
August 2002 4 3 20
September 2002 * * *
July 2003 13 11 28
August 2003 16 13 32
September 2003 * * *
Interior 18 July 2002 15 10 40
August 2002 * * *
September 2002 15 7 60
July 2003 17 13 33
August 2003 15 13 26
September 2003 32 12 135
Margin 4 July 2002 9 6 29
August 2002 8 7 19
September 2002 4 2 33
July 2003 10 8 22
August 2003 11 10 21
September 2003 6 4 26
Margin 15 July 2002 21 16 42
August 2002 * * *
September 2002 5 2 37
July 2003 22 13 62
August 2003 9 7 24
September 2003 25 11 95
*could not compute population estimate
Effects of Urban Development on Herpetofauna – Goode et al. 22
Table 9. Abundance estimates of side-blotched lizards (Uta stansburiana) on mark-recapture
plots at the Stone Canyon study area near Oro Valley, Arizona, in 2002 and 2003. LCI = lower
confidence interval, UCI = upper confidence interval.
Plot Month Year Abundance LCI UCI
Control 8 July 2002 16 12 34
August 2002 21 17 36
September 2002 31 20 66
July 2003 * * *
August 2003 180 45 955
September 2003 49 36 82
Control 11 July 2002 * * *
August 2002 17 13 33
September 2002 31 22 57
July 2003 25 10 88
August 2003 57 41 98
September 2003 46 30 88
Interior 15 July 2002 * * *
August 2002 37 26 68
September 2002 41 31 67
July 2003 128 27 724
August 2003 44 23 114
September 2003 75 50 135
Interior 18 July 2002 10 8 25
August 2002 37 31 57
September 2002 37 26 68
July 2003 28 18 58
August 2003 64 41 124
September 2003 57 47 81
Margin 4 July 2002 * * *
August 2002 10 8 23
September 2002 20 8 80
July 2003 * * *
August 2003 22 13 63
September 2003 33 22 66
Margin 15 July 2002 12 9 33
August 2002 13 11 27
September 2002 16 14 28
July 2003 * * *
August 2003 32 25 56
September 2003 25 19 49
*could not compute population estimate
Effects of Urban Development on Herpetofauna – Goode et al. 23
Mark-Recapture Results - Uta
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Abundance
C-8 15.6 21.2 31.2 48.8
C-11 16.7 30.6 24.9 57.0 45.5
I-15 36.5 40.9 43.9 75.2
I-18 10.5 37.5 36.7 27.5 63.9 57.5
M-4 10.0 19.5 22.4 32.7
M-15 12.2 13.2 15.8 32.2 25.4
Jul-02 Aug-02 Sep-02 Jul-03 Aug-03 Sep-03
Figure 9. Population estimates for side-blotched lizards (Uta stansburiana) by month and by
year at the Stone Canyon study site near Oro Valley, Arizona.
Mark-Recapture Results - Urosaurus
0
5
10
15
20
25
30
Abundance
C-8 8.47 1.65 5.2 3.67
C-11 10.25 4.25 2.8 25.05
I-15 1.72 2.71 3.45 3.9
I-18 6.01 10.25 4.25 2.8 25.05
M-4 4.13 2.09 5.09 2.51 2.02 3.86
M-15 5.6 5.67 10.03 3.15 16.96
Jul-02 Aug-02 Sep-02 Jul-03 Aug-03 Sep-03
Figure 10. Population estimates for tree lizards (Urosaurus ornatus) by month and by year at
the Stone Canyon study site near Oro Valley, Arizona.
Effects of Urban Development on Herpetofauna – Goode et al. 24
We obtained data on body size for each age class for both tree lizards (Table 10) and side-blotched
lizards (Table 11). Adult tree lizards were more commonly observed than juveniles, however, the
opposite was true for side-blotched lizards. Tree lizard hatchlings (n = 3) and side-blotched lizard
hatchlings (n = 8) were infrequently observed. Adult female tree lizards varied in mean SVL from
45.8 mm on control plot 11 to 48.3 mm on margin plot 15. Adult male tree lizards varied in mean
SVL from 48.7 mm on interior plot 11 to 50.6 mm on control plot 8. Adult female side-blotched
lizards varied in mean SVL
Table 10. Body size by age class data for tree lizards (Urosaurus ornatus) caught during mark-recapture
sampling at the Stone Canyon study site near Oro Valley, Arizona, in 2002 and 2003.
N
SVL (mm)
(mean + se)
SVL
Range
Mass (g)
(mean + se)
Mass
Range
Control 8
Hatchlings 2 26.7 + 2.8 23.9-29.5 0.6 + 0.2 0.5-0.8
Juveniles 4 37.3 + 2.7 32.8-44.9 1.5 + 0.2 0.9-2.1
Adult Females 10 47.5 + 0.4 45.7-50.0 3.4 + 0.1 2.8-3.8
Adult Males 13 50.6 + 0.6 46.5-53.6 3.8 + 0.1 3.1-4.6
Control 11
Hatchlings 0
Juveniles 7 37.3 + 2.4 30.4-44.9 1.8 + 0.4 0.9-3.3
Adult Females 4 45.8 + 0.2 45.5-46.5 2.5 + 0.0 2.4-2.6
Adult Males 6 50.4 + 0.7 48.0-53.5 3.9 + 0.2 3.2-4.7
Interior 15
Hatchlings 1 25.0 0.6
Juveniles 2 40.1 + 0.9 39.2-40.9 2.5 + 0.4 2.1-2.8
Adult Females 6 46.9 + 0.5 45.0-48.5 3.6 + 0.1 3.2-3.9
Adult Males 13 48.7 + 0.5 46.0-52.0 3.5 + 0.1 2.9-4.6
Interior 18
Hatchlings 0
Juveniles 9 36.8 + 2.2 30.5-44.5 1.8 + 0.3 0.9-3.3
Adult Females 12 47.0 + 0.4 45.0-49.5 3.2 + 0.2 1.8-4.2
Adult Males 13 49.7 + 0.6 46.3-52.2 3.6 + 0.1 2.9-4.1
Margin 4
Hatchlings 0
Juveniles 6 42.0 + 2.2 31.0-44.9 2.4 + 0.3 0.8-3.0
Adult Females 9 47.3 + 0.5 45.0-50.0 3.5 + 0.1 3.1-4.4
Adult Males 12 49.6 + 0.6 45.0-53.0 3.5 + 0.2 2.0-4.6
Margin 15
Hatchlings 0
Juveniles 6 34.3 + 1.7 31.0-41.8 1.3 + 0.2 0.8-2.0
Adult Females 16 48.3 + 0.5 45.0-51.7 3.3 + 0.2 1.9-4.6
Adult Males 16 50.3 + 0.4 47.5-52.7 3.7 + 0.1 2.7-4.4
Effects of Urban Development on Herpetofauna – Goode et al. 25
from 45.0 mm on margin plot 4 to 47.4 mm on control plot 11. Adult male side-blotched lizards
varied in mean SVL from 46.3 mm on margin plot 4 to 47.2 mm on three different plots of different
types. Mean mass of both species also varied among plots. Adult female tree lizards ranged from
2.5 g on control plot 11 to 3.6 g on interior plot 15. Adult female side-blotched lizards varied in
average mass from 3.0 g on interior plot 15 to 3.5 g on control plot 11. Adult male tree lizards were
least massive on margin plot 4 and interior plot 14 at 3.5 g and most massive on control plot 11 at
3.9 g. Adult male side-blotched lizards varied from 3.3 g on control plot 11 to 3.7 g on control plot 8.
Table 11. Body size by age class data for side-blotched lizards (Uta stansburiana) caught during
mark-recapture sampling at the Stone Canyon study site near Oro Valley, Arizona, in 2002 and
2003.
N
SVL (mm)
(mean + SE)
SVL
Range
Mass (g)
(mean + SE)
Mass
Range
Control 8
Hatchlings 2 28.4 + 0.6 27.8-29.0 0.8 + 0.2 0.6-0.9
Juveniles 34 37.0 + 0.6 30.0-41.6 1.8 + 0.1 1.0-2.9
Adult Females 12 46.4 + 0.6 42.0-50.0 3.2 + 0.2 2.3-4.1
Adult Males 19 47.2 + 0.6 42.7-51.0 3.7 + 0.1 2.5-4.5
Control 11
Hatchlings 1 29.0 0.8
Juveniles 30 37.9 + 0.5 32.0-41.9 1.8 + 0.1 1.2-2.5
Adult Females 8 47.4 + 0.8 42.0.4-49 3.5 + 0.2 2.4-4.2
Adult Males 23 46.4 + 0.7 42.0-52.4 3.3 + 0.1 2.4-5.2
Interior 15
Hatchlings 2 26.5 + 2.5 24.0-29.0 0.6 + 0.1 0.5-0.7
Juveniles 41 36.9 + 0.4 30.6-41.3 1.8 + 0.1 1.1-2.4
Adult Females 10 45.1 + 0.8 42.0-50.5 3.0 + 0.2 2.5-4.2
Adult Males 22 47.2 + 0.7 42.0-51.8 3.6 + 0.1 2.5-4.6
Interior 18
Hatchlings 2 25.3 + 1.3 24.0-26.5 0.7 + 0.2 0.5-0.9
Juveniles 51 37.3 + 0.4 30.0-41.5 1.8 + 0.1 1.0-2.7
Adult Females 9 45.8 + 0.8 42.5-49.1 3.0 + 0.2 2.0-3.9
Adult Males 33 46.6 + 0.6 42.7-54.2 3.5 + 0.1 2.4-4.8
Margin 4
Hatchlings 1 28.0 0.9
Juveniles 15 36.6 + 1.0 31.0-41.9 1.8 + 0.1 0.9-3.0
Adult Females 3 45.0 + 1.0 43.0-46.5 3.1 + 0.2 2.8-3.4
Adult Males 12 46.3 + 0.9 42.5-51.5 3.5 + 0.2 2.5-4.8
Margin 15
Hatchlings 0
Juveniles 30 37.1 + 0.6 31.9-41.5 1.7 + 0.1 1.1-2.6
Adult Females 7 46.4 + 0.7 43.0-49.0 3.2 + 0.2 2.4-3.8
Adult Males 21 47.2 + 0.5 44.0-52.1 3.5 + 0.1 2.7-4.9
Effects of Urban Development on Herpetofauna – Goode et al. 26
It is difficult to discern any obvious patterns in body size of tree lizards and side-blotched lizards. It
appears that there is considerable natural variation in these parameters, even between sites that are
only separated by a short distance. The variation we observed in body size of these common lizards
may prove to be important when assessing potential effects of the development. The same is true of
age class differences across plots. It is obvious that highly localized effects can lead to detectable
changes in lizard body size and population structure. The effects wrought by the development will
occur at different scales, but it seems likely that the scale at which we have conducted mark-recapture
efforts is appropriate to the scale at which the development can be expected to have an effect.
Road Cruising
We observed a total of 261 amphibians and reptiles during road cruising surveys (Table 2). We
observed 134 toads of 3 species (Table 12), 43 lizards of 7 species, and 84 snakes of 11 species (Table
13). No tortoises were found while conducting road cruising surveys, although several tortoises were
incidentally observed crossing roads while driving from place to place during daytime research
activities. We also calculated the number of miles required to find an individual animal.
Table 12. Numbers of toads found on different road surfaces at the Stone Canyon study site
near Oro Valley, Arizona, in 2003.
Individuals Observed Miles/Individual
Species Dirt Paved Golf Path Dirt (49.8)
Paved
(121.4)
Golf Path
(493.1)
Bufo alvarius 1 35 300 49.8 3.5 1.6
Bufo punctatus 8 38 459 6.2 3.2 1.1
Bufo cognatus 0 3 41 40.5 12.0
Scaphiopus couchii 0 0 7 70.4
Total 9 76 807 5.5 1.6 0.61
Road cruising is primarily effective for finding nocturnally active toads, snakes, and lizards. When
compared to other methods, road cruising was the second most effective way to find snakes (Figure
8); however, if effort is taken into consideration, road cruising is the most effective means of finding
snakes. Some road cruising occurs during daylight hours just before and after sunset, when some
typically diurnally active species exhibit a spike in activity (e.g., spiny lizards, Sceloporus spp.).
However, we conducted the vast majority of road cruising surveys after dark.
Overall, we found substantially more amphibians and reptiles on paved roads than on dirt roads
(animals found on golf cart paths are discussed in the next section). We found one toad every 1.6
miles of paved road driven, and one snake or lizard every 3.8 miles of paved road driven. The most
common toad species, and for that matter any species, found was the red-spotted toad at one
individual every 3.2 miles of paved road driven. The most common reptile species was the western
diamond-backed rattlesnake at one individual found every 15.6 miles of paved road driven.
Road cruising will be an excellent technique for assessing the potential effects of development in the
future, and we have established an excellent baseline to which to compare. Roads are usually the first
component of a development to be constructed, because they provide access to the myriad of people
(e.g., construction workers, real estate professionals, potential buyers) involved in converting natural
Effects of Urban Development on Herpetofauna – Goode et al. 27
desert to urban environment. The entire infrastructure of the development is dependent on roads. We
took advantage of the presence of roads to gather baseline data that can be repeated for as long as the
development exists.
Table 13. Numbers of reptiles found on different surfaces (dirt road, paved road, golf cart path)
at the Stone Canyon study site near Oro Valley, Arizona, in 2002 and 2003.
Individuals Observed Miles/Individual
Species Dirt Paved Golf Path Dirt Paved Golf Path
Callisaurus draconoides 0 2 1 205.1 633.3
Chilomeniscus cinctus 0 3 4 136.7 158.3
Coleonyx variegatus 1 17 93 186.7 24.1 6.8
Cophosaurus texanus 0 1 1 410.1 633.3
Crotalus atrox 2 26 13 93.4 15.8 48.7
Crotalus molossus 1 11 15 186.7 37.3 42.2
Crolatus tigris 4 18 34 46.7 22.8 18.6
Heloderma suspectum 6 4 17 31.1 102.5 37.3
Hypsiglena torquata 0 5 2 82.0 316.7
Lampropeltis getula 0 0 1 633.3
Leptotyphlops humilis 0 0 1 633.3
Masticophis flagellum 0 1 0 410.1
Micruroides euryxanthus 0 2 1 205.1 633.3
Phrynosoma solare 0 7 8 58.6 79.2
Pituophis catenifer 4 4 2 46.7 102.5 316.7
Rhinocheilus lecontei 0 3 2 136.7 316.7
Salvadora hexalepis 0 1 0 410.1
Sceloporus clarki 0 1 10 410.1 63.3
Sceloporus magister 0 0 1 633.3
Tantilla hobartsmithi 0 0 9 70.4
Thamnophis cyrtopsis 0 0 4 158.3
Trimorphodon biscutatus 1 1 10 186.7 410.1 63.3
Uta stansburiana 0 1 4 410.1 158.3
Total 19 108 233 9.8 3.8 2.7
Total Species 7 18 21
Total Miles 186.7 410.1 633.3
We found 7 amphibians of 3 species (all toads) and 40 reptiles of 17 species (8 lizards and 9 snakes)
dead on roads during the course of the study. Not surprisingly, most of the road-killed animals we
found were on paved roads (27) during the day and were generally diurnally active species (e.g., 7
regal horned lizards, 6 coachwhips, 4 patch-nosed snakes). We found 18 dead animals on the golf cart
path, most of which were diurnal lizards that were likely ran over by maintenance workers who travel
the cart paths with mowers, utility carts, and other equipment. We only found 2 animals dead on the
dirt roads, but one was a tiger rattlesnake that was run over at night by the only vehicle we ever
observed on the dirt road at night. Unfortunately, we were responsible for the deaths of 7 animals,
Effects of Urban Development on Herpetofauna – Goode et al. 28
most of which were small toads and banded geckos that can be very difficult to see at night and often
run towards the vehicle, making them difficult to avoid.
Large numbers of animals are killed on roads, providing an opportunity to examine mortality related
to urbanization. The relatively small number of individuals that we found during the course of this
study can be easily explained by the low volume of traffic at the site. Stone Canyon is a gated
community, and even though only a relatively small number of houses are currently occupied, the
gatehouse has been manned almost from the time construction began. Access to the site is tightly
controlled, which has had the effect of minimizing traffic. However, traffic from construction workers
and people involved in managing the site, including a large golf course maintenance staff, has led to
moderate traffic during daylight hours. We rarely see vehicles on the road at night other than the
occasional automobile belonging to one of the few residents living in the southern part of the
development.
Although traffic volume is low, we have observed people, primarily involved in construction, driving
at high speeds on the roads. The road-killed animals that we have observed are primarily diurnal
species, indicating that they were likely run over by construction workers.
As the development grows and more people come to live in Stone Canyon, we expect traffic volume
to increase dramatically, leading to a significant increase in road mortality. Other researchers have
found that the number of amphibians and reptiles killed on roads can be alarmingly high (reviewed in
Trombulak and Frissell 2000). Indeed, the problem of road mortality is considered an important issue
by the conservation community as evidenced by an entire issue (Volume 14, Number 1) of the journal
Conservation Biology that was devoted to ecological effects of roads on wildlife.
Herpetofauna are perhaps more vulnerable to road mortality than other vertebrate species, because
they are terrestrial, relatively slow moving, and commonly use roads to thermoregulate. One study
(Rosen and Lowe 1994) estimated that approximately 175 snakes per kilometer are killed on Highway
85 where it passes through Organ Pipe Cactus National Park in the southern Arizona. At Saguaro
National Park, a short distance from our study site in upland desert that is very similar to the Stone
Canyon site, biologists have conservatively estimated that approximately 51,000 vertebrates die every
year on park roads (N. Kline, Saguaro National Park, personal communication). Amazingly, of the
51,000 vertebrates killed on roads, 44,000 were amphibians and reptiles (mostly toads at night and
lizards during the day).
Some species are particularly vulnerable to road mortality. For example, turtles and tortoises are
vulnerable, because they are slow to reproduce, meaning that even the death of a few individuals can
have a negative impact on a population. Snakes may be more susceptible to road kill because they
tend to be stretched out on roads and are difficult to avoid by motorists. Adding to the problem with
snakes is the fact that some people are known to intentionally run them over. Toads, especially
explosive breeding desert species such as those found at the Stone Canyon study site, come out in
huge numbers on rainy summer nights to breed. Breeding sites often include roadside ponds created
by drainage ditches, resulting in large numbers of toads being killed on adjacent roads. In reality, we
feel that road kill will end up being the most significant source of mortality for herpetofauna at Stone
Canyon. Although, this may be mitigated by the fact that Stone Canyon is essentially a community of
winter residents, and amphibians and reptiles are rarely found on roads during the cold winter months.
Effects of Urban Development on Herpetofauna – Goode et al. 29
Golf Path Surveys
We spent 186.6 hours (Table 2) and traveled 633.3 miles while conducting golf path surveys (Table
13). Our data on toads only includes 493.1 miles, because we did not start counting toads until 2003
(Table 12). During golf path surveys we observed 807 toads, which differs from the figure of 1338
presented in Table 2, because it only includes toads found on the cart path and not during pond
surveys. We observed 233 reptiles belonging to 21 species, 125 of which were lizards (93 banded
geckos and 17 Gila monsters) and 98 of which were snakes (the large majority of which were
rattlesnakes).
We found one toad every 0.61 miles of golf path driven and one snake or lizard every 2.7 miles of golf
path driven. The most common toad species, and for that matter any species, found was the red-spotted
toad at one individual every 1.1 miles of golf path driven. The most common reptile species
was the banded gecko at one individual found every 6.8 miles of golf path driven. Interestingly, the
most common snake found on the golf cart path was the tiger rattlesnake at one individual per 18.6
miles of golf path driven.
The number of amphibians and reptiles found dead on golf cart paths (18) was higher than we
expected, especially compared to roads (29). Therefore, our results suggest that the number of
amphibians and reptiles killed on roadways will be higher at Stone Canyon, or at any other
development that includes golf courses than at a comparably sized development that does not have
golf courses.
The opportunity to conduct golf path surveys is probably the most unique aspect of this study. The
golf cart path traverses rocky terrain where it is not practical to build much larger roads. Therefore,
we were able to conduct extensive surveys in areas that would have to be surveyed on foot. Also, the
golf path runs through the middle of the development, rather than around the edge, so the potential for
effects of the development to be detectable seem greater. Finally, because the golf cart path is
adjacent to the golf course, and surrounded by heavily irrigated, landscaped vegetation, it should allow
us to directly assess effects of the golf course itself on herpetofauna. In a recently funded AGFD
project, we will be assessing the effects of golf courses of varying ages, including the Stone Canyon
course, on amphibians and reptiles.
Unfortunately, we did not obtain permission to survey golf paths until early September of 2002. Golf
path surveys immediately proved to be very successful, and we began cruising the golf paths as often
as possible. In 2003, we surveyed golf paths several nights per week and observed a large number of
toads, snakes and nocturnally active lizard species. In addition, we observed larger numbers of
smaller snake species (e.g., banded sand snakes, Chilomeniscus cinctus; southwestern black-headed
snakes, Tantilla hobartsmithii) than during road cruising, presumably because golf carts travel at a
slower rate of speed, and observers are closer to the roadway, making it easier to detect small animals.
We also found a much greater number of tiger rattlesnakes and lyre snakes, two of our focal species,
on golf cart paths, presumably because they are both primarily saxicolous species and the golf path
travels through relatively rocky areas.
Incidental Reptile and Amphibian Observations
We incidentally observed 686 reptiles (numerous toads were incidentally observed, but not recorded)
during the study, which included 89 tortoises, 241 lizards, and 356 snakes during the two-year study.
All reptiles observed while radiotracking tiger rattlesnakes and walking or driving to and from study
Effects of Urban Development on Herpetofauna – Goode et al. 30
plots were classified as incidental. We were unable to determine the number of incidental
observations per unit effort, because we did not keep track of time while traveling to and from plots.
Also, because we were not specifically searching for amphibians and reptiles during these times, we
felt that comparing what we found to other methods of finding animals would not be legitimate. For
example, we found a large number of tortoises during mark-recapture sampling, but our efforts were
focused on finding lizards. Even so, we found 24 tortoises on plot M-4. It seems likely that we
would have found considerably more tortoises if we were targeting them in our searches. Perhaps
this is an indication of the high density of tortoises found on site.
Incidental observations can be important, especially when compiling a species list for an area, and
when obtaining additional individuals of focal species, such as snakes for radiotelemeter
implantation. However, it is difficult to quantify effort expended in finding incidentals, so comparing
results to time-based survey results is probably not legitimate. One way to make incidental
observations more useful is to record the observers’ activity when the animal is observed. At least
this way, incidental observations can be compared among survey methods. We did not always
record our activity when encountering incidental amphibian and reptiles. This led to problems when
compiling data for reporting purposes. We could not easily or quickly address these problems,
because the number of incidental observations was high, and it would require that we go through the
records one by one. Nevertheless, we incorporated our incidental observations into this report when
we felt that it was important to do so.
Morphology of Focal Species
Raw data for all focal species are shown in Appendix A. We summarized processing data for tiger
rattlesnakes (Table 14). Male tiger rattlesnakes were longer and more massive than females. We also
summarized body size data by gender and age class where possible for 6 focal species (Table 15).
Table 14. Summarized processing data for all tiger rattlesnakes (Crotalus tigris) captured at the
Stone Canyon study site near Oro Valley, Arizona, from 2002-2003.
Parameter Females Males
% Adult 36.1% 63.9%
SVL 598 + 9.1 635.1 + 8.0
Mass 190.3 + 10.2 239.8 + 11.4
Head Length 26.1 + 0.4 28.0 + 0.5
Head Width 18.9 + 0.3 20.9 + 0.6
Number of Segments 7.5 + 0.4 7.9 + 0.3
Rattle Length 32.3 + 1.7 37.4 + 1.2
% with Broken Rattle 64.0% 66.0%
Body size data can be important for a variety of reasons. For example, data on length and mass can be
used to calculate a condition index, which is presumably related to health. Snakes that are more
massive per unit body length are probably healthier, and in turn, are likely to reproduce more. By
examining body size of snakes before and after development occurs, we may be able to detect
important differences. Below, in the section on potential effects of the golf course, we explore this
possibility further.
Effects of Urban Development on Herpetofauna – Goode et al. 31
Table 15. Sex ratios and body size data for all individuals captured of 6 focal species at the
Stone Canyon study site near Oro Valley, Arizona, from 2002-2003.
Species (F:M) Sex SVL Mass
Crotalus atrox (26:35) Females 853.2 + 28.5 494.1 + 74.2
Males 934.6 + 26.9 660.6 + 70.4
Crotalus molossus (19:24) Females 833.9 + 19.2 367.5 + 37.9
Males 852.9 + 23.8 432.5 + 36.7
Crotaphytus collaris (23:19) Females 86.7 + 0.9 24.2 + 1.2
Males 95.5 + 1.5 34.0 + 1.9
Gopherus agassizii (33:61) Females 237.3 + 3.1
Males 238.9 + 3.6
Heloderma suspectum All 298.4 + 6.5 384.6 + 18.7
Phrynosoma solare (22:24) Females 103.1 + 3.3 59.1 + 3.5
Males 87.0 + 1.5 40.9 + 3.1
Demography of Focal Species
We summarized age-class data for all three rattlesnake species present at the study site (Figure 11).
Age Class by Species (Crotalus spp.)
0
10
20
30
40
50
60
70
80
CRTI CRMO CRAT
Species
N
Neonates
Juveniles
Adults
Figure 11. Age class data for all three rattlesnake species present at the Stone Canyon study site
near Oro Valley, Arizona, from 2002-2003. CRTI = Crotalus tigris, CRMO = Crotalus molossus,
CRAT = Crotalus atrox.
Effects of Urban Development on Herpetofauna – Goode et al. 32
Age class data of tiger rattlesnakes and black-tailed rattlesnakes are heavily biased towards adults,
although the same cannot be said for western diamondback rattlesnakes, of which we found more
neonates than adults. In general, neonate and juvenile snakes are very difficult to find, and tiger
rattlesnakes and black-tailed rattlesnakes are no different. However, young-of-the-year western
diamond-backed rattlesnakes are relatively common, especially in late summer and early fall. In fact,
we found more neonate than adult western diamond-backed rattlesnakes during the study. To clarify,
thirteen of the neonate western diamond-backed rattlesnakes we observed were from a single litter
born to a gravid female that we captured near the golf course. The remaining 23 “neonates” were
actually young-of-the-year that had already dispersed. We termed these snakes neonates to
distinguish them from juveniles, which are snakes that are in their second year of life, but have not yet
reached the minimum SVL for which the species is known to reproduce. We found nearly as many
young-of-the-year western diamond-backed rattlesnakes as we did adults (n = 28).
Why young western diamond-backed rattlesnakes are common and young tiger and black-tailed
rattlesnakes are so rare is an interesting question. Perhaps it is because western diamond-backed
rattlesnakes have larger litter sizes on average, larger young at birth, and they grow to a much larger
adult size. The reason is apparently not related to the number of adults at our site, because both tiger
and black-tailed rattlesnakes were more common than western diamond-backed rattlesnakes. It will
be interesting to see if the development has differential effects on rattlesnake species. One might
predict that the strongest effect will be on western diamond-backed rattlesnakes, because their young
are more easily found, and may be exposed to more danger than the other two species.
We also summarized age class data for three focal lizard species and tortoises (Figure 12). Age
classes for all focal species were heavily biased towards adults. Monitoring age class distributions to
Age Class by Species
0
10
20
30
40
50
60
70
80
90
100
CRCO HESU PHSO GOAG
Species
N
Juveniles
Adults
Figure 12. Age class data for three lizard species and tortoises present at the Stone Canyon
study site near Oro Valley, Arizona, from 2002-2003. CRCO = Crotaphytus collaris, HESU =
Heloderma suspectum, PHSO = Phrynosoma solare, GOAG = Gopherus agassizii
Effects of Urban Development on Herpetofauna – Goode et al. 33
see if they change with increasing development may prove to be useful. Theoretically, development
could lead to a variety of changes in population structure, depending on the species. For example, if
reproduction is affected by anthropogenic influences such as increased mortality or increased
availability of resources such as water, then age class structure may change. If reproduction increases,
then we may see a shift towards an overall younger population, or age at maturity could even decrease
if animals are able to obtain larger body sizes relatively sooner.
We determined size class distributions for all focal species by sex, except for Gila monsters, for which
we were unable to determine gender reliably. Tiger rattlesnake males and females were strongly
skewed towards large adults, and the largest individuals were males (Figure 13). Black-tailed
rattlesnakes were biased towards adults, but individual males and females were more widely
distributed across adult size classes (Figure 14). Western diamond-backed rattlesnakes were biased
towards smaller individuals (obviously echoing age class structure), and juveniles were nearly absent
from our sample (Figure 15). We observed more large Gila monsters, but SVL tended to be relatively
evenly distributed among size classes (Figure 16). Desert tortoises were biased towards larger
individuals, although we found numerous individuals that we were unable to reliably sex, indicating
that they were not yet reproductively mature (Figure 17). Regal horned lizards were biased towards
intermediate sized males, but larger females, and we observed numerous individuals that were
apparently subadults (Figure 18). Collared lizards were biased towards larger individuals, with males
being slightly larger than females; juvenile collared lizards were absent from our sample (Figure 19).
CRTI Size Class Distribution
0
2
4
6
8
10
12
14
16
18
250-300
300-350
350-400
400-450
450-500
500-550
550-600
600-650
650-700
700-750
750-800
SVL (mm)
N
Females
Males
Figure 13. Size class distribution of 83 tiger rattlesnakes (Crotalus tigris) from the Stone
Canyon development near Oro Valley, Arizona, from 2002-2003. Note the obvious bias towards
large adults and the paucity of neonate and juvenile snakes.
Effects of Urban Development on Herpetofauna – Goode et al. 34
CRMO Size Class Distribution
0
1
2
3
4
5
6
350-400
400-450
450-500
500-550
550-600
600-650
650-700
700-750
750-800
800-850
850-900
900-950
950-1000
1000-1050
SVL (mm)
N
Females
Males
Figure 14. Size class distribution of 42 black-tailed rattlesnakes (Crotalus molossus) from the
Stone Canyon development site near Oro Valley, Arizona, from 2002-2003. Note the bias
towards adults, but not any particular size class for either sex.
CRAT Size Class Distribution
0
2
4
6
8
10
12
14
300-350
350-400
400-450
450-500
500-550
550-600
600-650
650-700
700-750
750-800
800-850
850-900
900-950
950-1000
1000-1050
1050-1100
1100-1150
SVL (mm)
N
Females
Males
Figure 15. Size class distribution of 61 western diamond-backed rattlesnakes (Crotalus atrox)
from the Stone Canyon development site near Oro Valley, Arizona, from 2002-2003. Note the
bias towards neonate and young-of-the-year snakes.
Effects of Urban Development on Herpetofauna – Goode et al. 35
When monitoring effects of environmental change on wildlife, biologists tend to focus on more
traditional parameters such as population size. We contend that demographic traits such as age class
or body size distributions may in fact be more informative, especially given the fact that accurate
population size estimates can be difficult obtain. Therefore, our datasets pertaining to age and body
size for several species are likely to be of importance in determining potential effects of urban
development at the population level. The fact that we now have baseline data on a variety of species,
each with unique life history characteristics leading to potential differences in vulnerability to
disturbance, increases our ability to detect species-specific effects of development.
Larger individuals tend to be more conspicuous, which may be one reason why we generally tend to
find much larger numbers adult snakes and lizards. In the case of venomous snakes, such as the
rattlesnakes we studied, there may be important advantages of being large. For example, a large
rattlesnake is probably safe from all but the largest predators, because it presents a formidable threat.
However, when the predator is man, larger size leading to increased probability of detection may be a
serious disadvantage. One study on twin-spotted rattlesnakes, funded by AGFD, showed that snakes
from a heavily poached population were significantly smaller than snakes from unhunted populations
(Prival et al. 1999). It is not unreasonable to predict that large individual rattlesnakes will decrease in
numbers as more and more people come to live in the area, resulting in increased persecution of
rattlesnakes, a species group that is known to be heavily persecuted (Arena et al. 1995).
HESU Size Class Distribution
0
2
4
6
8
10
12
14
16
18
20
150-200
200-250
250-300
300-350
350-400
400-450
SVL (mm)
N
Figure 16. Size class distribution of 36 Gila monsters (Heloderma suspectum) from the Stone
Canyon study site near Oro Valley, Arizona, from 2002-2003. Note the relatively large number
of presumably subadult lizards, which is in contrast to size class distributions of three sympatric
rattlesnakes species in Figures 13-15.
Effects of Urban Development on Herpetofauna – Goode et al. 36
GOAG Size Class Distribution
0
5
10
15
20
25
30
35
40
50-100
100-150
150-200
200-250
250-300
300-350
MCL (mm)
N
Females
Males
Unknown
Figure 17. Size class distribution of 124 desert tortoises (Gopherus agassizii) from the Stone Canyon
study site near Oro Valley, Arizona, from 2002-2003. Note the relatively large number of individuals
that could not be reliably sexed, indicating that they are probably not yet reproductively mature.
PHSO Size Class Distribution
0
1
2
3
4
5
6
7
8
9
30-40
40-50
50-60
60-70
70-80
80-90
90-100
100-110
110-120
120-130
130-140
140-150
SVL (mm)
N
Females
Males
Unknown
Figure 18. Size class distribution of 48 regal horned lizards (Phryonsoma solare) from the Stone Canyon
development near Oro Valley, Arizona, from 2002-2003. Note the bias towards moderately sized males
and large females.
Effects of Urban Development on Herpetofauna – Goode et al. 37
CRCO Size Class Distribution
0
2
4
6
8
10
12
14
16
30-40
40-50
50-60
60-70
70-80
80-90
90-100
100-110
SVL (mm)
N
Females
Males
Unknown
Figure 19. Size class distribution of 46 collared lizards (Crotaphytus collaris) from the Stone Canyon
study site near Oro Valley, Arizona, from 2002-2003.
Spatial Ecology of Tiger Rattlesnakes
We captured 84 tiger rattlesnakes (Figure 20), the large majority of which were found while road
cruising or conducting golf path surveys (Figure 21).
Figure 20. Aerial photograph showing initial capture locations for 84 tiger rattlesnakes (Crotalus tigris)
at the Stone Canyon study site near Oro Valley, Arizona, from 2002-2003.
Effects of Urban Development on Herpetofauna – Goode et al. 38
Figure 21. Aerial photograph depicting the large number of tiger rattlesnakes (Crotalus tigris) found on
roads and golf cart paths at the Stone Canyon study site near Oro Valley, Arizona, from 2002-2003.
We implanted radiotelemeters into a total of 30 tiger rattlesnakes, 15 males and 15 females, which we
located 1,008 times (Figure 22).
Figure 22. Aerial photograph showing 1,008 radiotracking locations of 30 tiger rattlesnakes (Crotalus
tigris) at the Stone Canyon study site near Oro Valley, Arizona, from 2002-2003.
Effects of Urban Development on Herpetofauna – Goode et al. 39
We computed several space-use parameters based on the total number of locations for each tiger
rattlesnake (Table 16). Due to premature radiotelemetry failure, we were only able to track three
snakes for the entire length of the study. We tracked an additional four snakes for a few months in
2002 and all of 2003.
Table 16. Space-use and movement data by sex for all 30 tiger rattlesnakes (Crotalus tigris) radiotracked
at the Stone Canyon study site near Oro Valley, Arizona, from 2002-2003.
Snake Sex n Begin Date End Date
Total
Distance (m)
Distance/
Day (m)
MCP
(ha)
95%
AKF
(ha)
50%
Core
(ha)
172 F 26 2002/07/12 2002/10/11 1437 16 85457 18.3 0.7
174 F 46 2002/07/12 2003/04/23 1728 6 53606 12.5 0.3
187 F 31 2002/08/08 2003/05/20 1463 5 49812 14.1 0.7
194 F 30 2002/08/26 2003/05/20 602 2 9060 1.5 0.2
195 F 9 2002/08/30 2002/10/09 106 3 517 0.2 0.03
199 F 66 2002/09/04 2003/09/29 2005 5 11750 19.4 1.4
205 F 67 2002/09/16 2003/09/29 1588 4 34925 8.5 1.0
209 F 64 2002/09/28 2003/09/28 2437 7 91997 31.2 0.2
215 F 37 2003/06/09 2003/09/28 1178 11 7896 1.6 0.4
219 F 24 2003/07/01 2003/09/29 655 7 8683 2.2 0.7
225 F 19 2003/07/18 2003/09/29 785 11 17821 3.8 0.5
240 F 17 2003/07/30 2003/09/28 649 11 9951 2.2 0.1
242 F 14 2003/08/02 3003/09/29 832 14 34161 10.4 2.2
255 F 6 2003/08/23 2003/09/29 480 13 13212 6.7 1.2
262 F 6 2003/09/12 2003/09/29 220 13 4466 2.0 0.3
Mean
± S.E
1077
± 175
8.5
± 1.1
3.3
± 0.8
9.0
± 2.3
0.7
± 0.2
175 M 99 2002/07/13 2003/09/29 4758 11 95677 18.5 0.8
176 M 49 2002/07/15 2003/09/29 3157 7 71331 14.0 0.4
177 M 52 2002/07/17 2003/09/29 3051 7 57648 13.5 1.5
181 M 18 2002/07/23 2003/04/04 738 3 18883 4.2 1.8
183 M 30 2002/08/02 2003/05/20 1009 3 24681 5.8 0.4
184 M 50 2002/08/02 2003/09/29 5439 13 193886 46.4 2.8
196 M 68 2002/08/31 2003/09/29 4372 11 185818 32.1 2.8
200 M 62 2002/09/09 2003/09/29 4592 15 254597 34.8 2.7
214 M 22 2003/06/07 2003/08/03 636 11 16343 3.5 0.9
217 M 31 2003/06/21 2003/09/29 1724 17 48726 11.3 0.4
222 M 12 2003/07/08 2003/08/13 512 14 11701 4.1 0.2
226 M 18 2003/07/18 2003/09/29 1723 24 53054 10.8 0.6
235 M 11 2003/07/24 2003/09/29 733 11 14007 5.2 0.9
241 M 14 2003/07/31 2003/09/29 1544 26 45004 10.9 2.1
254 M 10 2003/08/22 2003/09/29 735 19 23143 9.2 2.4
Mean
± S.E
2315
± 452
12.6
± 1.7
7.4
± 2.0
15.0
± 3.3
1.3
± 0.2
On average, males moved over twice as far as females, and their home ranges were over twice as large
as females. Males also move farther per day than females, and their 50% core activity areas were
roughly twice as large as females. These movement and space-use patterns are similar to those for
tiger rattlesnakes that we have studied elsewhere in the Tucson Basin (Goode and Wall 2002).
Effects of Urban Development on Herpetofauna – Goode et al. 40
In order to compare active season (i.e., July 1 – September 30, which roughly corresponds to the
summer rainy season), we combined data from both years and then summarized space-use parameters
for individuals with > 20 locations (Table 17). Results were similar to those reported above for annual
space use and movement patterns in that males again moved over twice as far as females. However,
during the active season, male home ranges were three times larger than females and their core
activity areas were approximately five times greater than females.
Table 17. Active season space-use and movement data for 7 female and 8 male tiger rattlesnakes
(Crotalus tigris) at the Stone Canyon study site near Oro Valley, Arizona, for the time period from
July 1 – September 30 in 2002 and 2003 combined.
Snake Sex n Begin Date End Date
Total Distance
(m)
Distance/
Day (m)
MCP
(ha)
95%
AKF
(ha)
50%
Core
(ha)
172 F 23 2002/07/12 2002/09/30 708 9 2.1 3.7 0.4
174 F 28 2002/07/12 2002/09/30 1157 14 3.0 2.8 0.3
199 F 28 2003/07/02 2003/09/29 1135 13 4.6 9.1 0.6
205 F 26 2003/07/02 2003/09/29 1003 11 2.6 7.7 0.4
209 F 26 2003/07/02 2003/09/28 706 8 13.5 2.5 0.1
215 F 27 2003/07/02 2003/09/28 988 11 0.8 1.8 0.1
219 F 24 2003/07/01 2003/09/29 655 7 0.9 2.2 0.7
Mean
± S.E
907
± 81
10.4
± 1.0
2.1
± 0.5
4.3
± 1.1
0.4
± 0.1
175 M 29 2002/07/13 2002/09/30 1478 19 3.3 5.0 0.5
176 M 22 2002/07/15 2002/09/30 906 12 1.6 3.3 0.3
177 M 22 2002/07/17 2002/09/30 1744 23 3.3 6.6 0.5
175 M 31 2003/07/02 2003/09/29 1880 21 4.6 7.4 0.5
184 M 28 2003/07/02 2003/09/29 2437 27 10.3 28.7 0.5
196 M 21 2003/07/01 2003/09/29 2491 28 8.0 16.1 2.1
200 M 24 2003/07/02 2003/09/29 2937 33 12.6 28.1 8.2
217 M 28 2003/07/01 2003/09/29 1651 18 4.8 11.7 0.5
Mean
± S.E
1945
± 232
22.6
± 2.3
6.1
± 1.4
13.4
± 3.6
1.6
± 0.1
Tiger rattlesnakes are typical of rattlesnake species that have been studied in that males move farther
and have larger home range sizes (McCartney et al. 1987). Increased movement by males is probably
related to the polygynous mating system exhibited by tiger rattlesnakes (Duvall et al. 1992). The
mating system of tiger rattlesnakes is one in which receptive females are a scarce resource in any give
year, because they are unable to mate on an annual basis. Males essentially “compete” for females by
searching for and finding them. Mating takes place during the summer active season, which
corresponds to even greater movement by males relative to females.
Is it possible that development may lead to changes to the mating system? We believe it is possible, if
snakes using golf course areas that provide resources that are not normally available are able to store
more fat and therefore reproduce more frequently. If females become annual reproducers, the males
will no longer have to spend as much time searching for receptive mates. Monitoring the mating
system of these serpents as development proceeds is a novel approach that is much different than
traditional population size monitoring. The ability to obtain data on the behavioral ecology and
compare it in a before-after context is one of the main reasons we incorporated single-species research
into our study design.
Effects of Urban Development on Herpetofauna – Goode et al. 41
We also compared active season space-use and movement patterns between years for males (Table
18) and females (Table 19); however, caution should be used in interpreting results due to low sample
Table 18. Active season space-use and movement data for male tiger rattlesnakes (Crotalus tigris) at the
Stone Canyon study site near Oro Valley, Arizona, comparing 2002 with 2003.
Yr Snake Sex n Begin Date End Date
Total
Distance
(m)
Distance/
Day (m)
MCP
(ha)
95%
AKF
(ha)
50%
core
(ha)
2002 175 M 29 2002/07/13 2002/09/30 1478 19 3.3 5.0 0.5
2002 176 M 22 2002/07/15 2002/09/30 906 12 1.6 1.6 0.3
2002 177 M 22 2002/07/17 2002/09/30 1744 23 3.3 3.3 0.5
Mean
± S.E.
1376
± 247
18.0
± 3.2
2.8
± 0.6
5.0
± 1.0
0.4
± 0.1
2003 175 M 31 2003/07/02 2003/09/29 1880 21 4.6 7.4 0.5
2003 184 M 28 2003/07/02 2003/09/29 2437 27 10.3 28.7 0.5
2003 196 M 21 2003/07/01 2003/09/29 2491 28 8.0 16.1 2.1
2003 200 M 24 2003/07/02 2003/09/29 2973 33 12.6 28.1 8.1
2003 217 M 28 2003/07/01 2003/09/29 1651 18 4.8 11.7 0.5
Mean
± S.E
2286
± 235
25.4
± 2.7
8.1
± 1.5
18.4
± 4.3
2.3
± 1.5
Table 19. Active season space-use and movement data for female tiger rattlesnakes (Crotalus tigris) at the
Stone Canyon study site near Oro Valley, Arizona, comparing 2002 with 2003.
Yr Snake Sex n Begin Date End Date
Total
Distance
(m)
Distance/
Day (m)
MCP
(ha)
95%
AKF
(ha)
50%
core
area
2002 172 F 23 2002/07/12 2002/09/30 708 9 2.1 3.7 0.4
2002 174 F 28 2002/07/12 2002/09/30 1157 14 3.0 2.8 0.3
Mean
± S.E
932
± 225
11.5
± 2.5
2.5
± 0.5
3.3
± 0.5
0.3
± 0.1
2003 199 F 28 2003/07/02 2003/09/29 1135 13 4.6 9.1 0.6
2003 205 F 26 2003/07/02 2003/09/29 1003 11 2.6 7.7 0.4
2003 209 F 26 2003/07/02 2003/09/28 706 88 1.3 2.5 0.1
2003 215 F 27 2003/07/02 2003/09/28 988 11 7.7 1.8 0.1
2003 219 F 24 2003/07/01 2003/09/29 655 7 0.9 22.3 0.7
Mean
± S.E
897
± 93
10.0
± 1.1
2.0
± 0.7
4.7
± 1.5
0.4
± 0.1
sizes. During the monsoon season of 2003, male tiger rattlesnakes moved greater total distance and
distance per day than they did during the monsoon season of 2002. Males also had much larger home
ranges and core activity areas in 2003. Tiger rattlesnakes are known to move farther and more often
during years with higher precipitation (Goode and Wall 2002). We maintained three rain gauges at
the Stone Canyon study site, which were checked after every substantial rainfall event. Our data
indicate that there was very little difference in amount of total summer rainfall between years (Figure
23), although rainfall was distributed differently across July, August and September (Figure 24).
Effects of Urban Development on Herpetofauna – Goode et al. 42
Rainfall by Season
0
20
40
60
80
100
120
140
160
1 July - 30 September 2002 1 October 2002 - 30 June 2003 1 July - 30 September 2003
Season
Precipitation (mm)
Figure 23. Rainfall by “season” (summer monsoon and intervening “winter” rains) for 2002 and 2003
recorded and averaged from three rain gauges placed at different locations throughout the Stone Canyon
study site near Oro Valley, Arizona.
Summer Rainfall
0
10
20
30
40
50
60
70
80
90
100
July August September
Rainfall (mm)
2002
2003
Figure 24. Rainfall per month of the summer monsoon season for 2002 and 2003 recorded and averaged
from three rain gauges placed at different locations throughout the Stone Canyon study site near Oro
Valley, Arizona.
Effects of Urban Development on Herpetofauna – Goode et al. 43
Monsoon rainfall (i.e., July-September) was average (148 mm) in both years. However, “winter”
rains were only 50% of average (161 mm) in winter of 2002-2003. We conclude that rainfall was
probably not a determining factor in observed differences in movement patterns. A more likely
explanation is that sample size was greater and the length of the tracking period was longer in 2003.
More data are required to more thoroughly examine annual differences in movement patterns and
space use.
Our main goal was to examine movement patterns and space use relative to development. We plotted
minimum convex polygons for all 30 tiger rattlesnakes (Figure 25). The majority of snakes
established home ranges that included parts of the golf course and housing development. A smaller
number of snake home ranges did not include golf course and housing areas.
As the development progresses, tiger rattlesnakes whose home ranges include the golf course and
future residential areas will likely be encountered more frequently by humans. Some will turn up in
peoples’ back yards, and others will be encountered on road ways or by golfers and other people
involved in recreational activities. Still others will come in contact with landscapers, pool service
personnel and golf course maintenance staff. It will be interesting to see how tiger rattlesnakes react
to increased contact with humans. Tiger rattlesnakes are similar to other snake species that have been
studied in that they show strong fidelity to their home ranges. We often find snakes in the exact same
shelter sites from one year to the next, and they are often there at the same time of the year.
Sometimes, we find snakes at locations on the same day, exactly one year later.
Figure 25. Aerial photograph showing minimum convex polygon home ranges for 30 tiger
rattlesnakes tracked between July 2002 and October 2003 at the Stone Canyon development site
near Oro Valley, Arizona.
Effects of Urban Development on Herpetofauna – Goode et al. 44
Home ranges of tiger rattlesnakes at Stone Canyon will soon be occupied by houses and people. In
some cases, home ranges will include literally dozens of lots with houses, including locations that will
become the actual building pad for homes (Figure 26). It will be interesting to see if these snakes
continue to use their traditional home ranges, or if they are plastic enough to alter their home range use
and location.
Figure 26. Aerial photograph showing minimum convex polygon home ranges of two tiger
rattlesnakes (Crotalus tigris) at the Stone Canyon study site near Oro Valley, Arizona (2003),
that included lots that are either already developed, in the process of being developed, or will be
developed in the future.
Some tiger rattlesnake home ranges include areas of the development that will become a large resort
(Figure 27). Not only will their chances of encountering humans dramatically increase after the site is
developed, they will also lose a significant amount of otherwise useable habitat. The footprint of the
main resort and associated structures comprises a significant proportion of both snakes’ home ranges.
The question is whether or not enough open space will remain to satisfy the requirement of tiger
rattlesnakes. Connectivity of habitat patches will also be important to reduce the amount of time
rattlesnakes have to spend moving across unsuitable areas to reach patches. Perhaps the golf course
will play an important role in allowing tiger rattlesnakes to persist in the face of increasing human
habitation, because vegetation along the golf course is dense due to artificial irrigation.
We have observed tiger rattlesnakes using features of the golf course on numerous occasions. One
heavily used part of the golf course is the tee boxes (Figure 28). Tee boxes at the Stone Canyon golf
course are comprised of large rocks that have been piled up in order to elevate the tee box. These tee
Effects of Urban Development on Herpetofauna – Goode et al. 45
Figure 27. Aerial photograph showing home ranges of two tiger rattlesnakes (Crotalus tigris) in 2003
using the area that will become the Ritz-Carlton Resort, a large luxury hotel with numerous outbuildings
at the Stone Canyon development site near Oro Valley, Arizona.
Figure 28. Aerial photograph showing close-up view of tiger rattlesnake (Crotalus tigris) locations on golf
course tee boxes at the Stone Canyon study site near Oro Valley, Arizona, in 2003.
Effects of Urban Development on Herpetofauna – Goode et al. 46
boxes become artificial rock piles that are backfilled with dirt and then turf is placed over the top of
the rock pile. Interstitial spaces between rocks are apparently left behind, because the dirt does not
completely fill in between rocks. Rodent activity increases dramatically in the tee boxes, and
landscaped vegetation is planted around the edges of the turf and heavily irrigated. Tiger rattlesnakes
use these tee boxes in proportions much higher than their availability would predict. We term these
tee boxes “tiger rattlesnake condos” because we often find our radiotelemetered snakes using them.
Tiger rattlesnakes also used areas where human activity was high. One example was a snake that
spent most of the summer of 2003 in the immediate vicinity of the Stone Canyon Golf Club (Figure
29). On two separate occasions, golf course personnel told us that they saw the snake near the
clubhouse, and that golfers regularly observed the snake in the practice area. The snake was obvious,
because its rattle was painted, and most people working at the golf course and playing golf are aware
of our study. On one occasion, the snake was coiled on the concrete entryway to the clubhouse. The
fact that neither golf course personnel nor golfers killed or moved the snake indicates that snakes
(even rattlesnakes) are tolerated around the golf course. If this attitude can be maintained as the
development grows, it will likely play a critical role in the ability of rattlesnakes to persist in the area.
In this vein, we have recently received funding from AGFD to develop and educational program that
targets golfers, promoting coexistence of snakes and other herpetofauna inhabiting the site.
Figure 29. Aerial photograph showing several locations of tiger rattlesnake (Crotalus tigris)
#199 in the vicinity of the Stone Canyon golf course clubhouse at the Stone Canyon study site
near Oro Valley, Arizona (August-September 2003). The snake was observed on several
occasions by golfers and golf course personnel who reported that they had seen a rattlesnake
with a painted rattle. The photograph was taken in 2002.
Effects of Urban Development on Herpetofauna – Goode et al. 47
Tiger rattlesnakes tended to overwinter on rocky slopes above the golf course, however a few
individuals overwintered in rock outcrops on the golf course and in areas that will be developed in the
future (Figure 30). The destruction of den sites to make way for houses may have an inordinately
Figure 30. Red flags indicate the sites of tiger rattlesnake (Crotalus tigris) overwintering sites
(winter 2002-2003) at the Stone Canyon study site near Oro Valley, Arizona. Some snakes
overwintered on or immediately adjacent to the golf course, but most snakes moved up onto
rocky slopes above the golf course to spend the winter.
strong impact on snakes. Tiger rattlesnakes tend to use the exact same den sites from year to year,
although the presence of suitable habitat for the purposes of surviving the winter do not seem to be
limited given the overall rockiness of the area.
Many of the snakes that overwintered north of the golf course moved down onto the course during the
summer active season. In order to reach the golf course, snakes had to cross the main road that
encircles the golf course (Figure 31). The configuration of the landscape at the Stone Canyon site,
with the golf course area essentially serving as a summer activity range separated from a major
overwintering area by a road that will be heavily traveled in the future, presents a potential problem
that deserves management attention. We know that tiger rattlesnakes are commonly found along this
road as previously discussed. We also know that our radiotelemetered snakes frequently cross this
road, not only to reach the summer activity range, but as they move about their home ranges (e.g.,
Figure 32). Based on the fact that many of our radiotelemetered snakes centered their core activity
areas on the golf course (Figure 33), using man-made structures and landscaped vegetation, we can
only expect the situation to continue. Monitoring tiger rattlesnake use of the golf course and the
survival of individuals crossing roads compared to those away from roads will be important.
Effects of Urban Development on Herpetofauna – Goode et al. 48
Figure 31. Aerial photograph showing home ranges, tracking locations, and overwintering sites (red
triangles) of five tiger rattlesnakes (Crotalus tigris) at the Stone Canyon development site near Oro
Valley, Arizona. Overwintering sites were located on steep rocky slopes above the golf course, and
snakes had to cross the main road in order to utilize golf course surroundings.
Figure 32. Aerial photograph of an individual tiger rattlesnake (Crotalus tigris) crossing the road
multiple times while traversing its home range at the Stone Canyon study area near Oro Valley, Arizona.
N 0 500 m
Capture
Site
Effects of Urban Development on Herpetofauna – Goode et al. 49
Figure 33. Aerial photograph showing active kernel home ranges of three tiger rattlesnakes (Crotalus
tigris) at the Stone Canyon study site near Oro Valley, Arizona, in 2003. Red triangles indicate the
locations of overwintering sites. Active kernel home ranges consist of four isopleths, with the outermost
isopleth corresponding to a 95% probability that a given snake location will fall within its bounds. The
innermost isopleth is corresponds to a 10% probability that a given location will fall within its bounds.
Because a large number of locations fall into such a small area, it indicates that the snakes are
concentrating their activities within this area, which is referred to as a core activity area. The core areas
of all three snakes in this photograph are centered on the edges of golf course g