In the study, which is published in the current issue of Conservation Biology, the authors found that of the 80 groups of desert bighorn sheep known to have roamed California's mountains over the past century, 30 are now extinct.
In their investigation of the population decline, the researchers evaluated impacts ranging from contact with domestic livestock, which can lead to the spread of disease and competition for food, to poaching, mining, human disturbance and other factors. They also analyzed climatic variables such as temperature and precipitation that affect the availability of vegetation and dependable sources of spring water for the sheep.
"Climate was consistently correlated with extinction in a way the other factors weren't," said Clinton W. Epps, a doctoral student in environmental science, policy and management at UC Berkeley's College of Natural Resources and lead author of the paper. "The harsh environment inhabited by desert bighorn sheep already has them walking on a knife's edge. It doesn't take too much to push them off. The bottom line is that more than one-third of the populations that were once known are now gone," said Epps.
From 1901 to 1987, the mean annual temperature in the deserts of the southwestern United States increased by about 1.8 degrees Fahrenheit, which is considered significant by climatologists. In addition, annual precipitation dropped about 20 percent in southeastern California over the last century. According to the study, groups of bighorn sheep were more likely to be lost in lower elevation mountains where there were higher average temperatures and les
Contact: Sarah Yang
University of California - Berkeley