Arizona Kofa Sheep Herd Continue Decline
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 410 sheep.
The survey estimate is down from the 2008 survey estimate of 436 sheep, but it is still slightly above the lowest recorded estimated level of the 2006 survey of 390.
Due to standardized survey methodology and scientific margin of accuracy, biologists' analysis of the past four 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.
Seasonal rains were good, consequently habitat conditions are also favorable throughout the refuge. All of the sheep appeared healthy during the aerial surveys. Biologists observed lamb-to-ewe ratios of 26 lambs per 100 ewes, which is above the long-term average of approximately 20 lambs per 100 ewes for the refuge. However, a slightly higher lamb-to-ewe ratio has not yet translated into an increase in the population - it has only stabilized it.
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 U.S. Fish and Wildlife Service (USFW) and Arizona Game and Fish Department (AGFD) are conducting an ongoing, joint study to collect data on these and other suspected causes of the population's decline.
"We recognize the importance of Kofa's bighorn sheep and will continue to be proactive in managing this unique resource," said Mitch Ellis, manager of the Kofa National Wildlife Refuge Complex. "We're also confident that effective and appropriate wildlife management within the wilderness context of Kofa will be achieved."
In November 2007, 30 ewes were captured and fitted with tracking devices in order to monitor nutrition, movements, and mortality to assist in making active management decisions to assist in restoring the herd's population. The project study is scheduled to run through the fall of 2010.
"Kofa's bighorn sheep population is critically important to numerous small vulnerable bighorn sheep populations throughout the Southwest," said John Hervert, Wildlife Program Manager for Arizona Game and Fish. "If we are unsuccessful in restoring the bighorn sheep population in the Kofas, many of these populations will go extinct. The Kofa population is essential to the translocation efforts of the bighorn."
An extensive Web site dedicated to the Kofa NWR bighorn sheep is available at www.azgfd.gov/kofa. The AGFD launched the site 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.
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.
Because of the findings of the 2006 survey, no new translocations from the Kofa herd are scheduled. The last translocation of sheep from the Kofa was in 2005. The USFWS and AGFD continue their combined research and active management strategy in the pursuit of a desert bighorn sheep herd that can once again sustain a translocation program.
The USFWS and AGFD have jointly conducted Kofa bighorn sheep surveys since 1981. Prior to 1992, surveys were conducted annually. However, in 1992 funding constraints reduced the survey schedule to once every three years. Because of the 2006 survey results, annual surveys were temporarily reinstated. The AGFD organized funding using sportsman-generated department dollars and USFWS monies beginning in 2007.
The size, location, and unfragmented nature of 1,038 square miles that make up the Kofa NWR, have long been recognized as a unique combination that has made its 435 square miles of sheep habitat especially productive. With the passage of the 1990 Arizona Desert Wilderness Act, 856 square miles of the refuge have been designated as wilderness.