San Gabriel Survey Overview
Every year in February or March, the California Department of Fish and Wildlife organizes an event to count the population of bighorn sheep (Ovis candadensis nelsonii) in the San Gabriel Mountain Range. This survey is held with the support of the National Forest Service. This work is important as it indicates the overall health of the herd. This herd has been used in the past as a source population for translocation efforts to re-populate herds in the Mojave desert that have been extirpated. Due to the low carrying capacity of the desert habitat and the attendant small herd groups, it is a natural occurrence that some bands of bighorn sheep will die leaving the range vacant. It is also natural that the ranges with larger populations of bighorn would naturally re-colonize the vacant ranges. Biologists call this system of herds a metapopulation. However, through the development and occupation of the desert by humans, much of the natural repopulation efforts are not successful because man-made structures like highways, renewable energy developments and aquaducts have restricted bighorn movement. Translocations are thus necessary to properly manage and conserve the bighorn sheep such that future generations of humans may enjoy their presence.
The San Gabriel Survey utilizes a simultaneous ground and aerial count. Several bighorn sheep in the region has been marked and collared in the past. With re-sighting of the marked sheep and the overlapping aerial and ground crews, a reliable estimate of the population can be derived through statistical methods based on the actual observations. The ground crews are manned by volunteers from the general public. The DFW provides a mandatory orientation the evening before the count so that the volunteers can be educated in observation and classification techniques.
There are approximately nine trails that require volunteer groups: Lookout Mountain, Cattle Canyon, Day and Deer Canyons, Barrett-Cascade Canyon, South Fork of Lytle Creek, Middle Fork of Lytle Creek, Highway 39, Mt Baldy and the South Fork of Big Rock Creek.