Evaluation of distribution and trans-highway movement of desert bighorn sheep

              Evaluation of Distribution and
Trans- Highway Movement of
Desert Bighorn Sheep:
Arizona Highway 68
Final Report 588
Prepared by:
Kirby Bristow and Michelle Crabb
Arizona Game and Fish Department
Research Branch
5000 W. Carefree Highway
Phoenix, AZ 85086
August 2008
Prepared for:
Arizona Department of Transportation
206 South 17th Avenue
Phoenix, Arizona 85007
In cooperation with
U. S. Department of Transportation
Federal Highway Administration
The contents of the report reflect the views of the authors who are responsible for the facts and
the accuracy of the data presented herein. The contents do not necessarily reflect the official
views or policies of the Arizona Department of Transportation or the Federal Highway
Administration. This report does not constitute a standard, specification, or regulation. Trade or
manufacturers’ names which may appear herein are cited only because they are considered
essential to the objectives of the report. The U. S. Government and The State of Arizona do not
endorse products or manufacturers.
This report can also be found on our web site…
http:// www. dot. state. az. us/ ABOUT/ atrc/ Publications/ Publications. htm
Technical Report Documentation Page
1. Report No.
FHWA- AZ- 08- 588
2. Government Accession No. 3. Recipient's Catalog No.
4. Title and Subtitle
5. Report Date
August, 2008
Evaluation of Distribution and Trans- Highway Movement of Desert
Bighorn Sheep: Arizona Highway 68
6. Performing Organization Code
7. Author
Kirby Bristow and Michelle Crabb
8. Performing Organization Report No.
9. Performing Organization Name and Address
Arizona Game and Fish Department
10. Work Unit No.
Research Branch
5000 W. Carefree Highway
Phoenix, AZ 85086
11. Contract or Grant No.
JPA05- 018T/ KR05- 05551TRN
12. Sponsoring Agency Name and Address
ARIZONA DEPARTMENT OF TRANSPORTATION
206 S. 17TH AVENUE
13. Type of Report & Period Covered
FINAL REPORT
August 2005 - May 2008
PHOENIX, ARIZONA 85007
ADOT Project Manager: Estomih M Kombe
14. Sponsoring Agency Code
15. Supplementary Notes
Prepared in cooperation with the U. S. Department of Transportation, Federal Highway Administration
16. Abstract
We monitored desert bighorn sheep via satellite telemetry, remote cameras, and track beds between 2006
and 2007, to evaluate the effectiveness of the 3 design features ( underpasses) incorporated to facilitate
wildlife movement under State Highway 68 ( SR 68) between Kingman and Bullhead City, Arizona. We fitted
25 desert bighorn sheep with GPS radio telemetry collars and tracked movements in proximity to SR 68 for
15 months beginning in November of 2006. To evaluate use of underpasses by all ungulates we installed 5
remote passive infrared triggered cameras at each underpass. We monitored wildlife use at the underpasses
for 9,789 camera/ days and documented 25 crossing events by desert bighorn sheep (≤ 32 individual
crossings). None of the bighorns documented using the underpasses were ewes and no marked ewes
crossed SR 68. The majority ( 88%) of crossings by bighorns occurred at the easternmost underpass
( milepost 12.1), which also had the narrowest span and was located in the most rugged terrain. There were
3 crossings by bighorns at the westernmost underpass ( milepost 7.8), which had the widest span and was
located far from rugged terrain. No bighorns crossed at the remaining underpass ( milepost 10.8), however
other ungulates, such as wild burros ( 86%) and mule deer ( 14%), were seen more often there. At higher
levels, presence of other ungulates and humans may preclude bighorn use of underpasses. While proximity
to steep terrain, sight ability, underpass structure, and presence of other animals may all be important factors
affecting bighorn use of highway underpasses, placement of crossing structures relative to traditional travel
corridors of bighorns is likely the most important factor affecting their use.
17. Key Words
Arizona, desert bighorn sheep, Ovis Canadensis,
distribution, trans- highway movements, State Highway
68, connectivity, permeability, wildlife
18. Distribution Statement
No restriction. Document is available to the U. S.
public through the National Technical Information
Service, Springfield, Virginia 22161
19. Security Classification
Unclassified
20. Security Classification
Unclassified
21. No. of Pages
40
22. Price
SI* ( MODERN METRIC) CONVERSION FACTORS
APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By To Find Symbol
LENGTH LENGTH
in inches 25.4 millimeters mm mm millimeters 0.039 inches in
ft feet 0.305 meters m m meters 3.28 feet ft
yd yards 0.914 meters m m meters 1.09 yards yd
mi miles 1.61 kilometers km km kilometers 0.621 miles mi
AREA AREA
in2 square inches 645.2 square millimeters mm2 mm2 Square millimeters 0.0016 square inches in2
ft2 square feet 0.093 square meters m2 m2 Square meters 10.764 square feet ft2
yd2 square yards 0.836 square meters m2 m2 Square meters 1.195 square yards yd2
ac acres 0.405 hectares ha ha hectares 2.47 acres ac
mi2 square miles 2.59 square kilometers km2 km2 Square kilometers 0.386 square miles mi2
VOLUME VOLUME
fl oz fluid ounces 29.57 milliliters mL mL milliliters 0.034 fluid ounces fl oz
gal gallons 3.785 liters L L liters 0.264 gallons gal
ft3 cubic feet 0.028 cubic meters m3 m3 Cubic meters 35.315 cubic feet ft3
yd3 cubic yards 0.765 cubic meters m3 m3 Cubic meters 1.308 cubic yards yd3
NOTE: Volumes greater than 1000L shall be shown in m3.
MASS MASS
oz ounces 28.35 grams g g grams 0.035 ounces oz
lb pounds 0.454 kilograms kg kg kilograms 2.205 pounds lb
T short tons ( 2000lb) 0.907 megagrams
( or “ metric ton”)
mg
( or “ t”)
mg megagrams
( or “ metric ton”)
1.102 short tons ( 2000lb) T
TEMPERATURE ( exact) TEMPERATURE ( exact)
º F Fahrenheit
temperature
5( F- 32)/ 9
or ( F- 32)/ 1.8
Celsius temperature º C º C Celsius temperature 1.8C + 32 Fahrenheit
temperature
º F
ILLUMINATION ILLUMINATION
fc foot candles 10.76 lux lx lx lux 0.0929 foot- candles fc
fl foot- Lamberts 3.426 candela/ m2 cd/ m2 cd/ m2 candela/ m2 0.2919 foot- Lamberts fl
FORCE AND PRESSURE OR STRESS FORCE AND PRESSURE OR STRESS
lbf poundforce 4.45 newtons N N newtons 0.225 poundforce lbf
lbf/ in2 poundforce per
square inch
6.89 kilopascals kPa kPa kilopascals 0.145 poundforce per
square inch
lbf/ in2
SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380
TABLE OF CONTENTS
I. EXECUTIVE SUMMARY...................................................................................... 1
II. INTRODUCTION..................................................................................................... 3
A. STUDY AREA ................................................................................................... 4
III. METHODS.............................................................................................................. 11
A. CAPTURE AND TELEMETRY...................................................................... 11
B. CAMERAS AND TRACK BEDS.................................................................... 11
C. HABITAT SELECTION................................................................................... 12
IV. RESULTS................................................................................................................ 13
A. CAPTURE AND TELEMETRY...................................................................... 13
B. CAMERAS AND TRACK BEDS.................................................................... 17
1. Union Pass............................................................................................. 20
2. The Hole................................................................................................. 20
3. Arabian Mine ......................................................................................... 20
C. HABITAT SELECTION................................................................................... 22
V. ANALYSIS AND CONCLUSIONS.................................................................. 25
VI. RECOMMENDATIONS..................................................................................... 29
A. UNION PASS ................................................................................................... 29
B. THE HOLE ....................................................................................................... 29
C. ARABIAN MINE ............................................................................................. 30
VII. REFERENCES ..................................................................................................... 31
LIST OF FIGURES
Figure 1. Location of State Route 68 desert bighorn sheep study area in
northwestern Arizona. Study area extends along the highway between
Bullhead City east to Golden Valley, Arizona.................................................... 6
Figure 3. Union Pass wildlife underpass ( MP 10.8) on State Route 68 in
northwestern Arizona, 2005- 2007....................................................................... 7
Figure 3. The Hole wildlife underpass ( MP 10.8) on State Route 68 in
northwestern Arizona, 2005- 2007....................................................................... 8
Figure 4. Arabian Mine wildlife underpass ( MP 10.8) on State Route 68 in
northwestern Arizona, 2005- 2007....................................................................... 9
Figure 5. Movements of marked desert bighorn sheep that crossed State Route 68
in northwestern Arizona, 2005- 2007................................................................. 14
Figure 6. Movements of marked desert bighorn sheep that did not cross State
Route 68 in northwestern Arizona, 2005- 2007 ................................................. 16
Figure 7. Percent use of wildlife underpasses by humans and ungulates along
State Route 68 in northwestern Arizona, 2005- 2007 ........................................ 17
Figure 8. Desert bighorn sheep at the Union Pass underpass ( MP 12.1) exhibited
cautious behavior while traveling under roadways but seemed more
comfortable in the right- of- way near State Route 68 northwestern
Arizona, 2006- 2007 .......................................................................................... 19
Figure 9. Burro use was common at The Hole underpass ( MP 10.8) on State
Route 68 in northwestern Arizona, 2005- 2007 ................................................. 20
Figure 10. Human/ vehicle use was common at the Arabian Mine underpass on
State Route 68 in northwestern Arizona, 2006- 2007 ........................................ 21
Figure 11. Locations of marked desert bighorn sheep and escape terrain ( slope
60% or greater) in the area of State Route 68 in northwestern Arizona ............ 22
LIST OF TABLES
Table 1. Escape terrain ( slope 60% or greater), marked bighorn use within 1km
of underpasses, photo- documented bighorn crossing events, and index
of openness ( height x width)/( length) of wildlife underpasses on State
Route 68 in the Black Mountains, northwestern Arizona, 2005- 2007.............. 15
Table 2. Location of State Route 68 desert bighorn sheep study area in
northwestern Arizona. Study area extends along the highway between
Bullhead City east to Golden Valley, Arizona.................................................. 23
ACKNOWLEDGEMENTS
The Arizona Department of Transportation, Federal Highway Administration and the
Arizona Desert Bighorn Sheep Society provided funding for this research. We also thank
AGFD personnel R. Babel, E. Podoll, and T. Richins for field assistance in monitoring
marked bighorns and recovery of bighorn mortalities and collars. Sue Boe ( AGFD)
provided analytical and GIS assistance. We also thank helicopter pilot M. Brinkworth
( Papillon Helicopters), Ole Alcumbrec ( Veterinarian), J. Wills, K. Morgan, and T. Smith
( AGFD) for capture assistance. AGFD pilots E. Cash, B. Coffman, B. David, F. Sunde,
and S. Dubois assisted with aerial telemetry.
1
I. EXECUTIVE SUMMARY
Highway construction can affect desert bighorn sheep ( Ovis Canadensis) populations by
increasing habitat fragmentation and isolation which can impede access to critical
habitats, increase the effects of stochastic events and reduce gene flow. There is rapid
expansion of road networks near bighorn habitat and increased use of high animal
fencing along highways to reduce wildlife/ vehicle collisions. Proper design and
placement of wildlife crossing structures is crucial to allow for animal movement and
reduce the potential for habitat fragmentation.
Three wildlife crossing structures ( underpasses) were incorporated into the realignment
and improvement of State Route 68 between Kingman and Bullhead City - Arizona, to
facilitate movement of bighorn sheep. State Route 68 was realigned and widened from a
2- lane to a 4- lane highway over a 14 mile stretch from County Route 68 to Mile Post 14.
This was accomplished between the year 2000 and 2002. To evaluate the effectiveness
of the different underpasses we fitted 25 bighorn sheep with GPS radio telemetry
transmitters and tracked movements in proximity to the highway for 22.5 months
beginning in November 2006. To evaluate use of underpasses by all ungulates we
installed 5 remote passive infrared triggered cameras at each underpass.
We monitored wildlife use at the underpasses for 20 months ( 9,789 camera- days) and
documented 25 times where bighorn sheep crossed under the highway (≤ 32 individual
crossings). All except one ( whose gender couldn’t be determined) of bighorns
photographed by remote cameras at underpasses were rams. Crossings often occurred at
the beginning and end of the breeding season. None of the marked bighorn ewes crossed
the highway during the study. 88% of the crossings by bighorns occurred at the
easternmost underpass ( Union Pass), which also had the narrowest span and was located
in the most rugged terrain. There were three crossings by bighorns at the westernmost
underpass ( Arabian Mine), which had the widest span and was located far from rugged
terrain. No bighorns crossed at the remaining underpass. However, other ungulates such
as wild burros and mule deer were often seen there. At higher levels the presence of
other ungulates and humans may preclude underpass use by bighorns.
Bighorns moved quickly when traveling through the underpasses but seemed more at
ease, often stopping to browse, while in the right of way. We documented three times
when bighorns approached the easternmost underpass without crossing the highway.
This behavior is likely related to traffic levels but may be indicative of unfamiliarity with
the area and the general cautious nature of bighorn movement. Cautious behavior
documented during most crossings may be related to underpass structure. Highway
permeability could likely be enhanced with higher, more open structures. Underpasses
should have an index of openness1 greater than 75 to enhance visibility and increase
probability of use by bighorns.
1 : The index of openness is calculated by multiplying the height by the width and dividing the product by
the length : ( height x width)/ ( length)
2
Bighorn sheep follow traditional movement patterns, where travel corridors are learned
from older individuals. Rams often move long distance to access different ewe groups
during the breeding season. Use of underpass structures was more associated with
documented movement patterns of the bighorn sheep population than proximity to steep
terrain. While proximity to steep terrain, sight ability, underpass structure, and presence
of other animals may all be important factors affecting bighorn sheep use of highway
underpasses, placement of crossing structures relative to traditional travel corridors of
bighorns is likely the most important factor affecting their use.
Future crossing structures should be placed in traditional travel corridors connecting high
quality habitat with steep ( greater than 60% slope) rugged terrain on both sides of the
roadway. Unstable, loose, or unnatural substrates used to stabilize side slopes may
impede bighorn sheep use. Reducing structural diversity on abutments, such that shaded
areas are minimized while incorporating a trail half way up the side slopes will likely
enhance permeability.
Right- of- way fencing ( at least 2 meters high) should be maintained throughout bighorn
sheep habitat to guide bighorns to crossing structures and reduce bighorn sheep/ vehicle
collisions. Jump- outs ( 2.5 meters high or more) would reduce potential for bighorn
sheep/ vehicle collisions when right- of- way fences are breached.
3
II. INTRODUCTION
Substantial effort has been expended in the past three decades in the design and building
of mitigation passages across roadways. As human populations continue to grow in the
United States, there is increased demand for improved highways to handle higher traffic
volumes ( Federal Highway Administration 1998), allowing for increased vehicle speeds
on the nation’s roadways ( Cook and Daggett 1995). Increased traffic volumes and speeds
on highways potentially affect wildlife through direct mortalities and habitat
fragmentation ( Foster and Humphrey 1995, Hughes et al. 1996).
Collisions with wildlife occur often on Arizona’s highways, causing loss of human lives
and economic losses associated with vehicle damage. In 2006, 1,398 vehicle collisions
with animals were reported in Arizona; two persons were killed, and 276 were injured
( Arizona Department of Transportation 2006). Estimated mean property damage was
$ 8,200, estimated costs of injuries averaged $ 11,500, and estimated costs associated with
fatalities averaged $ 1,210,000 ( Arizona Department of Transportation 2006).
Three wildlife crossing structures ( underpasses) were incorporated into the realignment
and improvement of 14 miles of State Route ( SR) 68 between Kingman and Bullhead
City - Arizona, to facilitate movement of wildlife, particularly desert bighorn sheep,
across the highway. Underpasses such as those incorporated into this redevelopment
have been widely used in the United States to mitigate effects of roadways on ungulate
movements and reduce collisions. However, few studies have addressed post-construction
efficacy of these measures ( Clevenger 1998, Clevenger et al. 2002).
Bighorn populations have declined throughout their historical range coincident with
European settlement of the West, possibly due to the introduction of diseases carried by
domestic animals ( Jessup 1985, deVos 1989), subsistence hunting, and habitat isolation
( Gionfriddo and Krausman 1986, Bleich et al. 1990). The bighorn population in the
Black Mountains near SR 68 is a sub- unit of the largest surviving bighorn population in
Arizona and is important in several respects, serving as the source herd for
reintroductions into several sites in Arizona and other southwestern states. The
population also provides enjoyment through wildlife watching on the study site and along
the Colorado River, as well as providing recreational opportunity to those who hunt
bighorns in the area.
Previous studies on the bighorns of the Black Mountains near Highway 93 indicate the
potential for adverse impacts of highway construction to this metapopulation. Research
on the Highway 93 alignment located approximately 30 miles to the north of this study’s
site documented bighorn movements across Highway 93 and suggested high vehicle-related
mortalities along a portion of U. S. Highway 93 could have serious implications
for the local population ( Cunningham and deVos 1992, Cunningham and Hanna 1992,
Cunningham et al. 1993, McKinney and Smith 2007). High right- of- way fencing ( more
than 2 meters/ 6.56 feet) installed as part of the improvement of SR 68 was designed to
reduce the potential for wildlife/ vehicle collisions. This might bisect the bighorn
population of the area if the wildlife crossings are impermeable to bighorn movement.
4
Bisecting this population would likely increase the risk of extirpation due to loss of
genetic exchange. Genetic diversity and population fitness is enhanced through genetic
exchange ( Diamond 1975, Mader 1984, Schwartz et al. 1986). The ability to move freely
can protect wildlife populations from random events such as introduction of diseases,
localized shortage of resources, predation pressure or other challenges to their survival
( Jessup 1985, Wilcox and Murphy 1985, deVos 1989, McKinney et al. 2003).
Research evaluating wildlife use of highway underpasses has focused primarily on
ungulates ( Clevenger 1998), but information on the use of underpasses by bighorns is
limited ( McKinney and Smith 2007). Information on bighorn movement patterns and
their use of underpasses in the vicinity of SR 68 is needed to enhance future efforts of
highway engineers, design specialists, and resource managers in incorporating wildlife
crossing structures and design features to increase public safety and ensure permeability
of the highway to wildlife. This will in turn reduce adverse impacts to the bighorn sheep
herd and increase the probability of population persistence. This information could also
have high economic returns on investment by assisting with the design of mitigation
features for future highway projects and potentially reducing construction costs due to
ineffective or unnecessary highway crossing structures. This type of information will
also enable resource managers to identify key habitat features regarding movements of
bighorn sheep, potentially minimizing adverse impacts of highway construction.
The objectives of the study were: 1) To determine if and how often large desert mammals
( mule deer, bighorn sheep, mountain lion, etc.) use the underpasses incorporated into the
SR 68 realignment; 2) To determine the movement patterns of bighorns in the vicinity of
SR 68 realignment, assess potential impacts to bighorn sheep distribution, and identify
trans- highway movements; 3) Identify factors potentially affecting use of underpasses by
bighorn sheep.
We assumed that use of underpasses by bighorns was related to the placement and
structure of the underpasses rather than traffic levels. This assumption is based on the
observation that few vehicles were exiting SR 68 within the study area. Therefore traffic
levels at each underpass should be nearly the same.
A. STUDY AREA
The study area was located in northwestern Arizona in the Black Mountains within 10
miles north and south of SR68 and was bounded on the west by the Colorado River and
to the east by Golden Valley. The elevation of the study area ranged from about 146m
( 479 ft) on the Colorado River to 1,496m ( 4907 ft.) in Golden Valley. The topography
ranged from mountainous terrain with steep talus slopes and rugged cliffs to dry washes
among rolling hills ( Cunningham and Hanna 1992). Average temperatures ranged from
31oC ( 88 º F) in summer ( May– September) to 12oC ( 54 º F) in winter ( December–
February). Rainfall was about 5.6 cm ( 2.18 in) and 4.7 cm ( 1.83 in) during summer and
winter respectively, and totaled about 15.4 cm ( 6 in) annually. Vegetation in the lower
bajadas, flats and desert wash areas is dominated by Creosote- bursage ( Larrea tridentata-
Ambrosia dumosa) while mixed- cacti and shrub communities predominate the
5
mountainous regions of the study area ( Brown et al. 1979). Predators on the study area
included bobcats, coyotes, gray foxes, and mountain lions. Domestic livestock were
infrequent in most of the study area, except that feral burros were common. Based on
aerial surveys, numbers of bighorns in the general area declined sharply between 2001
and 2004. Legal hunting of bighorns occurred during the month of December each year.
There were 3 underpasses incorporated into the realignment and improvement of SR 68
between Kingman and Bullhead City, Arizona to facilitate movement of wildlife,
particularly bighorns, across the highway ( Fig. 1). Union Pass at milepost 12.1 was 51m
wide, 25m high and 17m long ( 167ft, 82ft, and 56ft; Fig. 2). With good visibility through
the underpass, Union Pass had the shortest length of the three underpasses as it had no
median separating the east and west bound traffic lanes. The Hole at milepost 10.8 was
56m wide, 19m high and 38m long ( 184ft, 62ft, and 125ft; Fig. 3). It is characterized by
low visibility from both sides. Arabian Mine at milepost 7.8 was 116m wide, 18m high
and 37m long ( 380ft, 59ft, and 121ft; Fig. 4). The widest structure, Arabian Mine, was
not perpendicular to the wash that it crossed. Nonetheless, visibility inside as well as
across the underpass was good.
6
Figure 1. Location of State Route 68 desert bighorn sheep study area in northwestern
Arizona. Study area extends along the highway between Bullhead City east to
Golden Valley, Arizona.
7
Figure 2. Union Pass wildlife underpass ( MP 12.1) on State Route 68 in
northwestern Arizona, 2005- 2007.
8
Figure 3. The Hole wildlife underpass ( MP 10.8) on State Route 68 in northwestern
Arizona, 2005- 2007.
9
Figure 4. Arabian Mine wildlife underpass ( MP 7.8) on State Route 68 in
northwestern Arizona, 2005- 2007.
10
11
III. METHODS
A. CAPTURE AND TELEMETRY
Adult bighorns were captured from a helicopter using tranquilizer darting in November
2005 and using net- gunning in November 2006. GPS radio transmitter collars and unique
ear tags ( manufactured by Telonics, Inc. of Mesa, Arizona) were securely attached to all
bighorns. Transmitters were equipped with motion sensors triggering a specific mortality
signal if no animal movement occurred within 4 hours. Transmitters were designed to
provide a GPS location fix every five hours for the store- on- board transmitters and every
six hours for the spread- spectrum transmitters. All collars were programmed to
automatically disconnect and drop off animals after 22.5 months, for transmitter
recovery. Animal location data could be uploaded remotely from spread- spectrum
transmitters during a 3- hour window available every 14 days, and after final recovery.
Animal location data collected on store- on- board transmitters could be downloaded only
after collars dropped off and were recovered.
Aerial telemetry flights were conducted at least monthly and often bi- weekly between
November 2005 and September 2007 using fixed- wing aircraft. This facilitated the
download of data from spread- spectrum transmitters, the location of bighorns fitted with
store- on- board transmitters, and the documentation and location of mortalities. We
incorporated data from spread- spectrum transmitters into ArcGIS ® Version 8.3 software
( ESRI, Redlands, California) following each flight, and incorporated data from store- on-board
transmitters following collar drop- off and recovery at the end of fieldwork or when
transmitters were retrieved from mortality sites. For every case of mortality we identified
the cause of death based on signs found at the carcass site, including signs of disease,
presence of scat, tracks, caching of kill, and canine punctures.
Home ranges of marked bighorns were calculated using minimum convex polygons
( 100% MCP; White and Garrott 1990). The home ranges of individuals were also
described qualitatively in relation to SR 68. Highway crossings made successfully by
marked bighorns were determined by connecting consecutive GPS location fixes in
ArcGIS ® and identifying crossings where lines between fixes crossed SR 68. Whenever
possible, we verified the occurrence of crossings by marked bighorns using ground or
aerial telemetry. To estimate bighorn habitat use near underpasses we calculated the
number of locations of marked bighorns within 1 km buffers around the Union Pass, The
Hole, and Arabian Mine wildlife crossing structures.
B. CAMERAS AND TRACK BEDS
Five remote passive infrared triggered cameras were deployed at each of the three
underpasses along SR 68. We programmed 4 cameras ( manufactured by Reconyx, LLP
of Holmen, WI) to take 30 pictures ( one picture every quarter of a second) each time
movement was detected, and record date, time and temperature on each image. We
positioned cameras for full coverage of the underpass to record wildlife use of crossing
structures. We also positioned cameras to cover approach trails near the underpasses to
12
document wildlife that approached without crossing. One video camera ( manufactured
by Leaf River, Inc. of Taylorsville, MS) was deployed at each underpass and
programmed to take a 90 second video each time motion was detected, to better
document wildlife behavior in proximity to the highway.
We developed track beds at each of the three underpasses along SR 68 to supplement
data collected by the cameras. Each track bed was at least two meters wide and all were
of variable length depending on the underpass. We counted tracks once a week, and
cleared and restored track beds after each examination.
C. HABITAT SELECTION
To describe the configuration of underpasses we calculated an index of openness as
( height x width)/ ( length) for the Union Pass, The Hole, and Arabian Mine wildlife
crossing structures. To estimate availability of bighorn escape terrain in proximity to
wildlife crossing structures we calculated the amount ( km2) of area with slope ≥ 60%
( McKinney et al. 2003) within a 1 km buffer around the Union Pass, The Hole, and
Arabian Mine underpasses. To estimate land surface ruggedness throughout the study
area we calculated a Vector Ruggedness Measure ( VRM) for each 900m2 area
( Sappington et al. 2007).
To establish the characteristics of habitat availability we generated random points within
the MCP home range estimate for each marked bighorn. We plotted random points equal
to the number of bighorn locations used to calculate each MCP home range estimate
using ArcGIS ® . We overlaid all bighorn locations and random points on available GIS
habitat characteristic covers and recorded values for each of the following habitat
variables: Vegetation Type, Elevation, Slope, Aspect of Slope, and VRM. To predict
habitat use by bighorns we developed logistic regression models ( Hosmer and Lemeshow
1989) using habitat variables that were not correlated ( α< 0.1). We developed probable
models a priori, and calculated Akaike’s Selection Criterion ( AIC) to select the most
parsimonious model ( Burnham and Anderson 1992) and assigned 0.5 as the cut point for
classification of use and random sites.
13
IV. RESULTS
A. CAPTURE AND TELEMETRY
We captured and marked 25 bighorns in two capture efforts, and combined data from
them for our analyses. During the first capture, we deployed 10 spread- spectrum
transmitters ( six to females, four to males) and 10 store- on- board transmitters ( six to
females, four to males). In the second capture, we captured five animals ( two females,
three males) not captured before and deployed four spread- spectrum and one store- on-board
transmitters. In total we placed transmitters on six females and six males north of
SR 68, and eight females and five males south of SR 68.
There were 10 ( 40%) mortalities among the 25 marked bighorns during the study.
Mountain lion predation caused 5 ( 50%) of mortalities; known predation only occurred
north of the highway. Legal harvest ( 1; 10%), capture related mortality ( 1; 10%), and
poaching ( 1; 10%) caused fewer deaths than mountain lions. There were two mortalities
where cause of death could not be determined ( 20%).
We conducted 27 fixed- wing flights to upload data from spread- spectrum transmitters
and check mortality status of individuals. One transmitter stopped recording GPS points
after five months, one store- on- board transmitter failed and was unable to be recovered,
and one collar malfunctioned and dropped off almost a year early. We retrieved and
downloaded data from 13 operative transmitter collars after they all dropped off on
September 15, 2007. Twenty- four marked bighorns provided 38,790 usable GPS
locations.
Distribution and movements of marked bighorns generally occurred throughout the study
area but movement across the highway was rare ( Fig. 5). Bighorn ram locations within
1km of underpasses was greatest at Union Pass followed by Arabian Mine and then The
Hole ( Table 1). Bighorn ewe locations within 1km of an underpass were greatest at
Arabian Mine followed by Union Pass and then The Hole ( Table 1).
We documented eight crossings of SR 68 by three marked rams ( 12% of all marked
animals and 27 % of marked rams). Thus 88% of marked bighorns did not cross the
highway ( Fig. 6). We documented six crossings at Union Pass, one crossing at Arabian
Mine, and no crossings at The Hole. Evidence from remote cameras corroborated the
estimates of crossing locations. The remaining crossing by a marked animal that was not
recorded by remote cameras likely occurred between Arabian Mine and The Hole, in an
area where the right- of- way fencing was low ( less than two meters). Crossings by
marked bighorns occurred in both directions ( four heading north, four heading south.)
We calculated home ranges for 10 females and 10 males that were alive for more than six
months following capture and marking. Mean home ranges for females and males were
70.84 km2 (± 61.3 Standard Deviation) and 223.76 km2 (± 134.56 SD), respectively.
Mean home ranges of males that crossed ( mean = 277.09 km2, ± 220.52 SD) and those
that did not cross ( mean = 200.91 km2, ± 94.44 SD) the highway were similar.
14
Figure 5. Movements of marked desert bighorn sheep that crossed State Route 68 in
northwestern Arizona, 2005- 2007.
15
Table 1. Escape terrain ( slope 60% or greater), marked bighorn use within 1km of
underpasses, photo- documented bighorn crossing events, and index of openness
( height x width)/( length) of wildlife underpasses on State Route 68 in the Black
Mountains, northwestern Arizona, 2005- 2007.
Wildlife Underpass
Union Pass
The Hole
Arabian Mine
Escape Terrain ( km2) 0.28 0.17 0.02
Marked ram ( n = 10) locations 427 97 239
Marked ewe ( n = 14) locations 56 35 588
Bighorn crossing events 22 0 3
Index of Openness 75 28 56
16
Figure 6. Movements of marked desert bighorn sheep that did not cross State Route 68 in
northwestern Arizona, 2005- 2007.
17
B. CAMERAS AND TRACK BEDS
With remote cameras we documented 25 highway crossings by bighorns accounting for
up to 32 individuals ( Table 1). Only three crossings included two or more animals, the
rest were by single animals. All bighorns captured by cameras at underpasses were rams
except for one unknown. Bighorn movements across the highway were in both
directions, with 17 animals heading north and 15 animals heading south. 84% of bighorn
crossings occurred between May and October, which corresponds to the beginning and
ending of the breeding season. All bighorn crossings occurred between 8 am and 6 pm.
We documented three bighorn approaches that did not result in a crossing: all were on the
south side of the Union Pass underpass. Bighorns made up a relatively small proportion
of the animals using underpasses. Burros and humans accounted for the majority of
observed use followed by bighorns and deer ( Fig. 7). Data from track beds generally
corroborated results from the remote cameras. No mountain lions were documented
using the underpasses.
Ungulate and Human Crossings at Underpasses
0
10
20
30
40
Union Pass The Hole Arabian Mine
Site
Percent
Sheep
Burro
Deer
Human
Figure 7. Percent use of wildlife underpasses by humans and ungulates along State
Route 68 in northwestern Arizona, 2006- 2007.
All bighorns photographed on approach to underpasses were walking and exhibited
cautious, alert, ( vigilance) behavior. One bighorn was documented looking at a passing
vehicle before proceeding. Of the bighorns that crossed, 15 walked through the
18
underpass, 11 ran through it, and two both ran and walked. We were unable to accurately
categorize the behavior of four bighorns while they were directly under the roadway due
to lack of images. At the Union Pass underpass six bighorns ( 32%) stopped while under
the roadway and looked around, at some point each looked at a shadowed bench located
on the northeast corner of the abutment ( Fig. 8). Bighorns that crossed in a group did not
stop while under the roadway and the first half of animals that crossed in a group all
walked while the second half ran. Approximately 50% of the individuals that crossed
alone at Union Pass ran through the underpass. No bighorns were seen running after
crossing, and three were seen feeding close to the underpass after crossing ( Fig. 8).
19
Figure 8. Desert bighorn sheep at the Union Pass underpass ( MP 12.1) exhibited cautious
behavior while traveling under roadways but seemed more comfortable in the
right- of- way near State Route 68 northwestern Arizona, 2006- 2007.
20
1. Union Pass ( MP12.1)
Burros made the majority of the crossings at Union Pass, accounting for 53% followed by
bighorns at 25%, and finally humans at 22%. There were 22 crossings ( 29 individuals) by
bighorns at Union Pass. Bighorns that crossed the highway showed vigilance while
traversing through the underpass. This vigilance was reduced in the right of way on both
sides of the highway ( Fig. 8). There were a large number of foxes that used the
underpass, along with some coyotes and a few bobcats.
2. The Hole ( MP 10.8)
Burros accounted for 86% of crossings at The Hole ( Fig. 9), followed by deer at 14%.
There were no bighorns detected at this underpass. Bobcats commonly used The Hole to
cross under the highway; coyotes and foxes were rarely seen.
Figure 9. Burro use was common at The Hole underpass ( MP 10.8) on State Route 68 in
northwestern Arizona, 2006- 2007.
3. Arabian Mine ( MP 7.8)
Humans made up 71% of the Arabian Mine underpass users. Most were in vehicles with
a fair number stopping to rest in the shade of the underpass ( Fig. 10). Burros made up
28% of the crossings with bighorns and deer making up the remaining 1%. The bighorns
21
crossing at Arabian Mine exhibited the same vigilance behaviors as those documented at
Union Pass. Coyotes were occasionally seen at this underpass; foxes and bobcats were
rarely seen.
Figure 10. Human/ vehicle use was common at the Arabian Mine underpass on State
Route 68 in northwestern Arizona, 2006- 2007.
22
C. HABITAT SELECTION
The Union Pass structure had a higher index of openness than either The Hole or Arabian
Mine underpasses ( Table 1). The Union Pass structure also had more bighorn escape
terrain ( areas with slope greater than 60%) within 1km of the underpass than The Hole
underpass, which in turn had more than the Arabian Mine underpass ( Table 1 & Fig. 11).
Figure 11. Locations of marked desert bighorn sheep and escape terrain ( slope 60% or
greater) in the area of State Route 68 in northwestern Arizona.
23
We developed 5 different a priori habitat selection models based on competing theories
of factors affecting bighorn use ( Table 2). The global model including all available
habitat variables was the most parsimonious model describing bighorn habitat selection
( Table 2).
Table 2. Ranking of logistic regression models1 for marked bighorn ( n = 24) habitat use
in the Black Mountains near State Route 68, northwestern Arizona, 2005-
2007.
Model
K
- 2 log
likelihood
% bighorns
correctly
classified
% random
correctly
classified
AIC
Delta
AIC
1 Global 5 93,822.5 64.3 71.4 93,832.5 0
2 Migratory 3 97,569.4 62.8 66.9 97,575.4 3,742.9
3 Slope 1 99,605.8 58.4 69.0 99,607.8 5,775.3
4 Ruggedness 1 99,977.8 48.0 79.1 99,979.8 6,147.3
5 Vegetation 1 104,020.1 59.8 60.5 104,022.1 10,189.6
1 P- values for all models were < 0.001 ( n = 38,790), and degrees of freedom was equal to
the number of variables included in the model. Models are presented in order of
parsimony:
1 Global model; Vegetation type, elevation, percent slope, slope aspect, and VRM
2 Migratory model; Vegetation type, elevation, and percent slope
3 Slope model; percent slope only
4 Ruggedness model; Vector ruggedness only
5 Vegetation model; Vegetation type
24
25
V. ANALYSIS AND CONCLUSIONS
The impacts of highways constitute some of the more widespread factors altering natural
wildlife ecosystems. Collisions between vehicles and wildlife result in extensive human
deaths, injuries, and property damage ( Forman 2000). Impacts of highways on wildlife
populations are widespread: they block animal movements, reduce habitat connectivity,
fragment habitats and populations ( Forman 2000), and contribute directly to mortality of
wildlife.
We found that desert bighorn sheep used wildlife underpasses but that use was restricted
to 12% of marked animals and consisted of only rams. Reed et al. ( 1975) found 61% of
deer migrated safely using underpasses, 89% of mountain goat crossings were successful
( Singer and Doherty 1985), and up to 96% of elk used underpasses ( Waters 1988) in
various areas. Some studies indicate use of underpasses may increase over time ( Reed et
al. 1975, Singer and Doherty 1985, Waters 1988), but others reported reluctance for deer
to use underpasses even after 10 years ( Reed 1981).
Environmental features associated with underpasses influence their use by ungulates
( Clevenger 1998, Ng et al. 2004). The most commonly used underpass on SR 68, Union
Pass, had the highest availability of steep rugged terrain. Bighorn use of the Arabian
Mine underpass was higher than use of The Hole although availability of steep rugged
terrain was higher at The Hole. McKinney and Smith ( 2007) found bighorn use of
habitat near highways was associated with Continuous Linear Elevated Guideways
( CLEG), ridgelines that offered good visibility and connected habitats on both sides of
the highway. Although escape terrain ( 60% slope or higher) was more available near The
Hole, the main spine of the Black Mountains and associated CLEG was located well to
the east ( Fig. 3).
Bighorns follow established traditions in their movement patterns with young learning
seasonal movements and travel routes from adults ( Geist 1967). Marked bighorn
locations in the vicinity of Arabian Mine were more common than near The Hole. This is
an indication of a higher probability that bighorns would encounter that underpass. Thus
while proximity to steep rugged terrain likely affected underpass use by bighorns it may
have been less important than underpass placement relative to traditional movement
patterns. Due to the conservative nature of bighorn movement patterns ( Geist 1967),
maintaining traditional routes within a complex of habitat is critical to long term
population persistence ( Bleich et al. 1990). Underpasses located without reference to
established travel corridors may be ineffective in enhancing highway permeability to
wildlife ( Hanna 1982).
Bighorn crossings were more common at Union Pass than Arabian Mine despite the fact
that marked animal locations were more numerous near Arabian Mine. However, marked
bighorn locations near Arabian Mine were mostly ewes which we never documented as
crossing SR 68. Marked bighorn crossings of SR 68 were rare; the highway formed the
boundary of many home ranges. Bighorn use of underpasses on SR 68 was restricted to
rams and usually occurred during the six month period coincident with the beginning and
26
end of the breeding season. Bighorn rams often travel great distances during the breeding
season to access ewe groups. This behavior has evolved to ensure genetic diversity
among metapopulations in a naturally fragmented distribution ( Bleich et al. 1997).
Bighorn ram crossings of SR 68 are likely related to breeding behavior. Consequently the
permeability of SR 68 is critical to maintaining genetic diversity within the Black
Mountain habitat complex. Small, isolated populations, more than larger populations or
metapopulations, are subject to extinction through stochastic events and potential loss of
genetic heterozygosity ( Diamond 1975, Wilcox and Murphy 1985, Gaillard et al. 1998).
Desert bighorn sheep occur throughout northern Mexico and the southwestern USA and
are distributed in naturally fragmented populations, often as small, isolated demes as well
as metapopulations ( Krausman and Leopold 1986, Bleich et al. 1990, Andrew et al.
1999). Bighorn population persistence as it relates to population size is a controversial
topic among biologists, and whether association exists between these variables remains
contentious ( Berger 1990, Krausman et al. 1993, Wehausen 1999). In general, no
specific population size ensures population persistence ( Thomas 1990), but small bighorn
populations occupying marginal or comparatively poor habitat ( Berger 1990), or small
patches of suitable habitat ( Gross et al. 1997, McKinney et al. 2003) may require
management intervention to ensure long- term persistence. Conservation efforts should
emphasize preventing fragmentation and loss of habitat and restoring habitat
( Fahrig 1997).
Structural features of wildlife underpasses can affect ungulate use. On the other hand,
animals are unlikely to use areas where their predator avoidance strategies are
compromised ( Dodd et al. 2007). Bighorn predator avoidance behavior is dependent
upon the need for detecting threats from a distance ( Geist 1971, Krausman et al. 1999).
Narrow passages with reduced visibility can impede this ability. This may explain the
cautious behavior exhibited by bighorns while maneuvering through underpasses and the
avoidance of The Hole. The Hole had the lowest index of openness and was the only
underpass not used by bighorns.
Wildlife use of underpasses may be affected by the presence of other animals and high
human use ( Clevenger and Waltho 2000). Wild burros, and other animals can displace
bighorns at seasonally critical habitats ( Foster et al. 2005, Osterman et al. 2005 ), and
bighorns have been portrayed as poor competitors in social interactions ( Geist 1985).
Burro crossing use at Arabian Mine and The Hole ( Fig. 9) was higher than at Union Pass
which had the highest incidence of bighorn use. Human use was also high at Arabian
Mine ( Fig. 10) and bighorns may abandon areas associated with high human use
( Jorgenson 1988). Bighorns seek predictable environments to live in and may become
habituated to human activities that follow a predictable pattern ( Bristow et al. 1996).
Human activity at Arabian Mine however, was not predictable and vehicle traffic
intersected potential travel corridors for bighorns.
Our best model for habitat selection by bighorns included all five variables. One variable
was not sufficient to explain the habitat selection patterns of bighorn sheep throughout
the study area. Habitat quality encompasses relative environmental capability to provide
27
conditions associated with individual and population persistence ( Hall et al. 1997).
Bighorn habitat selection patterns are different between sexes and between different
seasons ( Bleich et al. 1997, Krausman et al. 1999). As rams disperse before breeding
seasons to access disparate ewe groups, their habitat selection patterns are likely different
from other seasons ( Bleich et al. 1997). Habitat evaluations designed to include habitat
selection patterns of dispersing rams could provide insights to placement of wildlife
crossing structures. McCarty and Bailey ( 1994) and McKinney et al. ( 2003) suggested
habitat evaluations should consider spatial requirements for viable bighorn populations.
Quantitative evaluations of habitat patches may provide insight into population
persistence and management implications of introducing bighorn sheep into unoccupied
locations, as well as for maintaining existing populations ( Caughley 1994, Fahrig and
Merriam 1994, Gross et al. 1997, Singer et al. 2001, McKinney et al. 2003).
28
29
VI. RECOMMENDATIONS
Design and placement of crossing structures will influence highway permeability for
bighorns, and more natural structures connecting suitable bighorn habitat will increase
their effectiveness. Connecting high quality habitat on both sides of the highway
especially in areas with escape terrain will increase the likelihood that a structure will be
encountered. Placement of structures should be along existing travel routes whenever
possible. Underpasses in particular need to have a high index of openness: ( height x
width)/ ( length); the higher and wider the more effective a structure will be. The index of
openness at Union Pass, the underpass used most by bighorns was 75 and may represent a
minimum since we documented three approaches that resulted in aborted crossings,
which could have been due to inadequate visibility. A higher index of openness would
likely have increased permeability at this site. Visibility through the underpass is critical
for animals approaching the structure. Underpasses whose sides have steep slopes and
loose substrates, or fence rip- rap to stabilize the sides may impede use or force bighorns
to cross at the bottom where predator avoidance strategies may be compromised. A shelf
or game trail below and extending the length of underpass abutments may provide easier
access and security to bighorns. Natural substrate with short, low- density vegetation
throughout the crossing structure may enhance permeability. Reducing structural
diversity on abutments such that shaded areas are minimized may reduce apprehensive
behaviors of bighorns and enhance permeability. Following are recommendations for
improvement of each of the existing underpasses.
A. UNION PASS ( MP12.1)
1) Recontouring the side slopes to remove the shadowed bench that is along the
abutment on the northeast side of the underpass could enhance bighorn use by
reducing vigilance behavior associated with that feature. Many bighorns crossing
at Union Pass stopped and looked with suspicion at the shaded area before
proceeding.
2) Stabilizing substrate along the steep slopes beneath the underpass and adding a
small game trail about half way up may increase bighorn use. Currently due to the
loose steep sides of the underpass the bighorns cross at the bottom, where their
predator detection/ avoidance strategies are compromised. A shelf below and
extending the length of underpass abutments may provide easier access and a
feeling of security for bighorns.
B. THE HOLE ( MP 10.8)
1) Many of the factors affecting bighorn use of underpasses — proximity to
traditional movement corridors, terrain features, index of openness, and presence
of other animals — are problematic at The Hole. The index of openness is likely
the only factor that could be addressed here. However, given the high burro use
and the relatively low probability that bighorns would encounter this site,
restructuring the underpass to increase the index of openness would likely be
ineffective.
30
C. ARABIAN MINE ( MP 7.8)
1) Reducing the amount of human activity at the underpass and preventing vehicle
access to the wash on either side of the highway at Arabian Mine may enhance
bighorn use.
2) Recontouring the side slopes to remove the shadowed bench that is along the
abutment on the northwest side of the underpass could enhance bighorn use by
reducing vigilance behavior associated with that feature. All the bighorns that
crossed here avoided this feature.
Right- of- way fencing height should exceed two meters throughout potential bighorn
habitats. We estimated that one marked ram crossed the highway in an area where right-of-
way fencing was low ( MP 8- 10), and the single bighorn/ vehicle collision was
documented in this same area. Right- of- way fencing between MP 8 and MP 10 should be
raised to two meters and this fencing height should also be extended east from MP 12.5
to MP 13, at the very least. Frequent monitoring of right- of- way fencing is necessary to
identify breaches that bighorns could use, especially in areas with high erosion potential.
Jump- outs designed to allow bighorns to climb up a ramp of rocks and jump out of right-of-
way fenced areas could reduce potential for bighorn/ vehicle collisions when right- of-way
fences are breached. Jump- outs should exceed 2.5 meters ( 8.2 ft) in height to ensure
that bighorns can not jump over into the right- of- way.
31
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