YUMA, Ariz. -- A new survey shows there are about 428 desert bighorn sheep on the U.S. Fish and Wildlife Service's Kofa National Wildlife Refuge in southwestern Arizona.
That's up from the 2010 survey estimate of 402 sheep.
The federal Fish and Wildlife Service and Arizona Game and Fish Department have jointly conducted Kofa bighorn sheep surveys since 1981.
Adjusting for margin of error and survey methodology, biologists say there has been no significant decline or improvement to the herd's population in the past six years.
Wildlife management agencies remain concerned about the low population levels on the refuge compared to the estimated 812 animals of the 2000 survey.
Experts attribute the decline to a variety of potential factors including drought, predators, water availability, disease and human disturbance.