United States Department of Transportation
i
Evaluation of measures to promote desert bighorn sheep highway permeability : U.S. Route 93.
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2014-01-01
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[PDF-3.23 MB]
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Abstract:This study evaluated desert bighorn sheep–highway relationships from 2008 to 2010 along a 17‐mi stretch of U.S. Route 93
(U.S. 93), in northwestern Arizona. Highway reconstruction between mileposts (MP) 2.3 and MP 17.0 was completed in October
2010. The research objectives were to:
Assess sheep movements, highway crossing patterns, distribution, and determine permeability.
Investigate spatial and temporal patterns of sheep highway crossings and relationships to traffic volume.
Investigate spatial and temporal sheep‐vehicle collision patterns.
Assess the impact of highway reconstruction activities on sheep movements, habitat use, and permeability.
Establish baseline data for pre‐ and during‐reconstruction movements, highway crossing and passage rates, and sheepvehicle
collisions against which to conduct a sound post‐reconstruction assessment.
Researchers instrumented 38 desert bighorn sheep (Ovis canadensis) with GPS collars. Sheep crossed the highway 340 times.
U.S. 93 constituted a significant barrier to sheep passage, as passage rates averaged just 0.07 crossings/approach. Passage rates
varied by season, with summer rates higher than winter and spring rates given that sheep exhibited increased tolerance to traffic
during summer when crossing U.S. 93 in pursuit of water. Sheep exhibited minimal response to consistently high traffic volume
encountered during the daytime hours when they were predominantly active.
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