The actions follow a petition filed by five environmental groups that asked the service to list the bighorn as endangered. This gives biologists the tools they need to save these magnificent symbols of the Sierra,'' he said. Jane Hendron, a spokeswoman for the Fish and Wildlife Service, said the unusual move was necessary because bighorn numbers have been steadily diminishing during the past few years, leaving no more than 100 alive today. Sierra Nevada bighorn never were particularly numerous, but it is thought that a few thousand roamed the high crags of the Sierra before the arrival of Europeans. After white settlement of California, their numbers rapidly diminished under relentless hunting and domestic sheep grazing.
Bighorns are extremely susceptible to livestock diseases.
By the late 1970s, only about a hundred were left. Through captive breeding and re-introduction programs, that number increased to more than 400 sheep in several different bands by the late 1980s. But the bighorns suffered an unexpected blow in 1990 with the passage of Proposition 117, which afforded cougars full protection. Cougars expanded in population, and some began preying on the sheep. Second, the lions kept the sheep off their traditional winter range.