Based on my observations at kill sites, it appeared to be almost entirely mountain lion predation. These and other observations have led some biologists to speculate that cougars might now be having more profound effects on ecosystems than was previously believed. The only reason I knew about this was that I had an intensive study going on for a significant period of time when this extinction occurred. Mule deer herds have also been significantly reduced by a combination of drought and cougar predation in some places in the Southwest. But biologists generally do not find that worrisome because deer have high reproductive rates and easily colonize new ground.
Biologists are concerned about other prey species, however.
If we're having a lot of local extinctions, we're losing all the genetics in those sub-populations. They stress that what may be true of cougar impacts in the Sierra Nevada might not be true elsewhere. Also, biologists believe that cougar numbers will eventually come down when the numbers of their prey diminish. There are still a lot of unknowns about the effects of cougar predation on prey populations, so it would be prudent for us to gather the facts first. In the meantime, California wildlife officials are now contemplating last-ditch efforts to save the Sierra sheep from extinction.