Populations remain low, management agencies’ concern is still high

The recently completed survey of the desert bighorn sheep population on the U.S. Fish and Wildlife Service’s Kofa National Wildlife Refuge in southwestern Arizona resulted in a population estimate of 428 sheep (95% confidence interval of 376 – 492). The survey estimate is up slightly from the 2010 survey estimate of 402 sheep, and is the highest estimate since the 2007 survey.

The apparent increase in the population size is not statistically significant, however, and biologists’ analysis of the past six surveys indicates no significant decline or improvement to the herd’s population. Wildlife management agencies remain concerned about the low population levels on the refuge compared to the estimated 812 animals of the 2000 survey. The U.S. Fish and Wildlife Service (USFWS) and Arizona Game and Fish Department (AGFD) have jointly conducted Kofa bighorn sheep surveys since 1981.

Once a very robust population, the size of the herd on the refuge has dropped significantly since 2000. Wildlife experts attribute the decline to a variety of potential factors including drought, predation, water availability, disease and human disturbance. Due to the significance of this sheep population, the USFWS and AGFD have instituted a comprehensive management program that addresses the suspected causes of the population’s decline. Predation management, water improvement and disease monitoring are some of the ongoing projects.

For the past 50 years, the Kofa has been an important source of desert bighorn sheep for the restoration and maintenance of bighorn populations across Arizona and throughout the southwestern United States, including New Mexico, Colorado, and Texas.

An extensive web site dedicated to the Kofa NWR bighorn sheep is available at www.azgfd.gov/kofa. Launched in November 2007, everything from the latest updates, background information, frequently asked questions, past press releases, active management activities and more can be found at this one-stop resource center.

Logo courtesy Arizona Game and Fish Department

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