The purpose of this site is to provide updates, background information, and references related to Arizona Game and Fish Department (AGFD) and U.S. Fish and Wildlife Service (FWS) efforts to sustain and restore the desert bighorn sheep (Ovis canadensis mexicana) herd that inhabits the Kofa Mountains Complex in Arizona. This complex includes the Kofa, Castle Dome, New Water, South Plomosa, Tank and Little Horn mountains. The largest contiguous portion of desert bighorn sheep habitat in the complex is contained within the Kofa National Wildlife Refuge (Kofa NWR) which historically has been home to a population averaging about 800 bighorns of this subspecies.
The 2006 survey of desert bighorn sheep populations in southwestern Arizona estimated the population on the U. S. Fish and Wildlife Service’s Kofa National Wildlife Refuge at 390 sheep, indicating the decline in refuge bighorn numbers noted during the 2003 survey is continuing and may be at or near the lowest levels previously recorded.
Bighorn from the Kofa have been the primary source of animals for the reestablishment and maintenance of bighorn populations across Arizona and throughout the southwestern United States, to include New Mexico, Colorado, and Texas. The regionally critical transplant program is halted until the population returns to historical numbers capable of supporting the transplants.
The most critical factors that influence wildlife populations are mortality and natality. Direct mortality of bighorn is most commonly caused by disease, hunting, predation, falls, drowning, or highway collisions. Indirect mortality factors include poor nutrition during drought, inter-specific competition for range/forage, habitat fragmentation, and excessive disturbance. The primary goal of management is to ensure wildlife populations are in balance with available habitat; that birth rates equal or exceed death rates. To ensure successful management, managers must be familiar with life history strategies of target species; must be able to detect changes in population size, distribution and structure; and must be able to quantify impacts of individual mortality factors that cumulatively affect population levels.
The bighorn population will be considered “recovered” when the population approaches the long-term average of 800 sheep, which, based on survey data since 1981, is considered the carrying capacity of the refuge. Population fluctuation between 600-800 sheep has been documented on several occasions and is considered normal.
Monitoring of mountain lion activity and predation through the collaring of lions and bighorn, use of remote wildlife water cameras, and reports of recreational users of the refuge will be a continuing part of the management of the herd. Removing lions whose predation has an adverse affect on the herd’s ability to sustain translocation activity will remain an available management tool.