Evaluation of Measures to Promote Desert Bighorn Sheep Highway Permeability: U.S. Route 93

The research team assessed desert bighorn sheep‐highway relationships from 2008 to 2010 along an 18‐mile stretch (mileposts 0−18.0) of U.S. Route 93 southeast of Hoover Dam and 70 miles northwest of Kingman, Arizona. The study section of the highway cuts through the northern extent of the Black Mountains where nearly 30 percent of the state’s total desert bighorn sheep population resides. Desert bighorn has long been a focal species of concern in planning for the Hoover Dam Bypass project begun in 2002. The environmental analysis addressed the impact of the widening on desert bighorn sheep travel corridors and habitat fragmentation, as well as the potential for increased sheep‐vehicle collisions. Extensive prior desert bighorn research supported the implementation of a comprehensive set of measures to maintain wildlife connectivity as part of highway reconstruction, including three wildlife overpasses and ungulate‐proof fencing.