Survival and Cougar Predation of Translocated Bighorn Sheep in Arizona

Abstract

We estimated survival and cause-specific mortality of 395 translocated bighorn sheep (Ovis canadensis) in Arizona, USA, from May 1979 to November 1997. To investigate regional and temporal trends, we compared survival among disjunct populations in 4 regions in Arizona (Northwest, Southeast, Southwest, Central) during 3 time periods: 1979-1985, 1986-1991, and 1992-1997. Survival did not differ among periods in the Northwest (P= 0.50) and Southeast (P= 0.78) regions, and ranged from 0.80 to 0.88 and 0.76 to 0.82, respectively. In contrast, survival decreased in the Southwest (P < 0.01) and Central (P< 0.01) regions, and ranged from 0.44 to 0.79 and 0.42 to 0.83, respectively. Cougar (Puma concolor) predation was the most important source of mortality (66%). Our results suggest that recent increases in cougar predation in most areas of Arizona may be responsible for declining bighorn sheep numbers. Recent population declines in mule deer (Odocoileus hemionus), the primary prey of cougars, may be responsible for recent increases of cougar predations on bighorn sheep in Arizona and other areas of western North America.