|Thursday, Aug 15, 2013|
In mid May, a National Park Service employee who was inspecting wildlife guzzlers (a tank that collects rainwater for wild animals to drink) 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 the animals were infected with pneumonia.
Scientists 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. To date, about thirty sheep carcasses have been identified. A helicopter survey in mid July indicated that there were significantly fewer sheep than have previously been surveyed in the vicinity of Old Dad Mountain, suggesting a large mortality event has occurred.
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. The herd at Old Dad Mountain was an important source for these programs, with about 200 animals captured and released in several other mountain ranges.
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 from domestic sheep or goats. Bighorn sheep have no natural resistance, and as a result, animals can become infected and die at a high rate. The few animals that survive become carriers, infecting new lambs that often die within a few months of birth. An outbreak such as this one typically causes a long term decline in the population that can last for more than a decade. Scientists believe that pneumonia outbreaks have reduced herds of bighorn sheep in western states by up to 90 percent.
An interagency working group has been formed to monitor the outbreak, suggest best practices for limiting effects of the disease, and provide recommendations for management actions. Members of the working group represent the California Department of Fish and Wildlife, National Park Service, Oregon State University, and affiliated researchers. Funding and staff for this work is provided by the Wild Sheep Foundation, Society for the Conservation of Bighorn Sheep, California Department of Fish and Wildlife, and the National Park Service.
Management actions currently under consideration include collaring healthy bighorn sheep in areas peripheral to the outbreak to monitor disease spread and determine sources of mortality, strategically using water sources to discourage connectivity between sub-herds in an attempt to limit disease spread, and removing clinically ill animals from the population to limit disease spread. Exact dates and implementation plans for these considered actions are in development.
For more information and updates, visit http://www.nps.gov/moja/naturescience/desert-bighorn-sheep.htm .