Respiratory disease has been detected in bighorn sheep in the area of Old Dad Mountain, 15 miles southwest of Baker, California. Observers have reported sick, dead, and dying bighorn sheep. Laboratory analysis has confirmed that these animals tested positive for pneumonia.
Bighorn sheep once roamed nearly every mountain range in Southern California and Nevada, but their numbers began to decline in the mid-1800s, as settlers and prospectors swept into the region.
By 1960, a century of impacts including disease, unregulated hunting, and habitat loss had greatly reduced California and Nevada's bighorn populations. Wildlife officials in both states launched bighorn sheep release programs to rebuild herds, moving animals from healthy herds to mountain ranges within their historic range.
But disease always looms as a threat to those gains. In 2010, pneumonia epidemics spread through bighorn populations in many western states. The disease typically enters into a population that has no resistance, and as a result, animals can become infected and die at a high rate. The few animals that survive are now carriers. New lambs catch the disease within a few months and die, so the population continues to decline. The disease typically effects a population for more than a decade. Scientists believe that pneumonia outbreaks have reduced herds of bighorn sheep in western states by up to 90 percent.
Pneumonia outbreak on Old Dad Mountain
In May 2013, a National Park Service employee who was inspecting wildlife guzzlers found four desert bighorn dead on Old Dad Mountain, 15 miles southeast of Baker, California. The employee also observed other sick animals that appeared to be weak and unsteady with labored breathing. Laboratory analysis of blood and tissue samples indicated that it had pneumonia. This disease may enter desert bighorn populations from domestic sheep or goats and is usually fatal to bighorn.
Biologists from the National Park Service and California Department of Fish and Wildlife have conducted field surveys to monitor the scope and spread of this wildlife disease outbreak. The terrain is difficult–steep, rugged, and remote. Using volunteers from the Society for the Conservation of Bighorn Sheep and the Sierra Club to expand their capacity, biologists have visited springs and guzzlers where bighorn congregate on Old Dad Mountain and in nearby areas to determine the extent and seriousness of the problem.
Scientists are considering what, if anything, they might try experimentally as they continue to monitor the outbreak. There are no good management options. One goal may be to attempt to prevent spread to outlying populations. With the rut beginning in the coming months, biologists believe the disease could spread rapidly as animals mix.