Arizona Game and Fish Department (AGFD) reintroduced 30 desert bighorn
sheep in 1980–1981 into an area of central Arizona. The population
grew to more than 200 animals by 1994, and then declined about 65%
or more through 1997 as drought conditions prevailed. From 1997 to
1999, the population tended to stabilize at a low level, and poor lamb
production continued. We began to study this population in 1999 to
evaluate factors possibly contributing to poor population performance,
including disease, nutritional status, and predators.
The bighorn sheep population under study is
located in the Mazatzal Mountains, and inhabits
a narrow band of rugged terrain contiguous
with the north sides of Apache, Canyon, and
Saguaro reservoirs on the Salt River, about
65 miles northeast of Phoenix.
Each October between 1989 and 2003, AGFD personnel monitored the population
and counted total bighorn, males, females, lambs, and yearlings observed,
to help evaluate population trends. We captured bighorn sheep using net
guns fired from helicopters between June 2000 and October 2002, and often
recaptured individuals. We placed mortality-sensitive radiocollars on each
captured animal to assess distributions and survival; these collars emit
a particular signal when they no longer record movement. We examined each
captured animal physically for disease symptoms, and collected blood, fecal,
and parasite samples to evaluate exposure to a wide variety of diseases.
We also measured forages for indications of overuse, and collected fecal
samples from adults and lambs to determine diet and nutritional
status of the population. We monitored predation directly by locating carcasses
of bighorn and attempting to determine cause of death, and indirectly by
measuring occurrence of bighorn remains in scats deposited by bobcats,
coyotes, and mountain lions. This research project is scheduled to end
June 30, 2004. The study will end and a final report will be completed
on June 30, 2004.
Our findings will benefit conservation and management of desert bighorn
sheep populations by increasing understanding of factors that affect their
performance, persistence, and management. Results also will benefit conservation
and management of bobcats, coyotes, and mountain lions through better understanding
of predator ecology and predator:prey relationships.
For more information
Larisa Harding, Arizona Game and Fish Department, 5000 W. Carefree Highway, Phoenix, AZ 85086-5000,
Phone: (623) 236-7301, Email: Lharding@gf.state.az.us