RETURNING ENDANGERED SIERRA NEVADA BIGHORN SHEEP TO YOSEMITE'S WILDERNESS.
Thomas R. Stephenson; California Department of Fish and Wildlife; 787 N Main St, Bishop, CA, 93514; (760) 937-0238; tom.stephenson@wildlife.ca.gov; Sarah L. Stock, John D. Wehausen

Species restoration projects have become increasingly more common on national park lands where endangered wildlife species are less subject to widespread threats, such as habitat destruction and livestock. Since the 1970s, endangered Sierra Nevada bighorn sheep (Ovis canadensis sierrae) have been the focus of large-scale recovery efforts spanning the southern and central Sierra Nevada that encompass three national parks. In 1914, Sierra bighorn were declared extirpated from Yosemite National Park. Here we describe reintroduction and augmentation efforts that returned Sierra bighorn to Yosemite and that recently approached the recovery goal of 50 yearling and adult ewes in the Yosemite area. However, the population remains vulnerable to malnutrition, disease, avalanche accidents, predation, and genetic inbreeding. This effort supports the concept that while a large population can ride out these threats, a small population requires judicious tracking of survival and reproduction, and the willingness to intervene by reintroducing and augmenting bighorn from source herds into previously occupied areas.  Translocations are an essential conservation approach for recovering many endangered species.  Yet source stock for translocations may be limited when relying on the availability of animals within endangered populations.  Consequently, using optimal numbers of individuals to meet desired thresholds may not be possible.  By the 1970s, bighorn remained in only 3 adjacent relic subpopulations in the Sierra Nevada.  The California Department of Fish and Wildlife, in cooperation with federal agencies, reintroduced Sierra Nevada bighorn sheep to create 8 additional subpopulations during 1979 – 2015.   We moved 173 animals (104 females, 69 males) through a combination of initial reintroductions and subsequent augmentations.  All reintroduced subpopulations persisted but growth rates varied among populations; initial population size, predation, and winter severity clearly drove growth rates.  The effects of behavioral and genetic factors were more loosely linked to growth rates.  We used resource selection functions to evaluate habitat preferences following reintroductions.  Relatedness of translocation stock appeared to increase herd cohesion and likely foraging efficiency.  Reintroduced populations typically required a minimum of 20 - 30 years to reach numbers considered sufficient to avoid extinction based on population viability modeling.  We recognize that the initial number of reintroduced individuals was low yet they were the maximum that could be moved without jeopardizing source populations.  Establishing a widespread metapopulation protected the species from local effects of predation and severe weather in recent years and should buffer the effects of future climate change.  Recognition of the time required for reintroduced populations to become fully established is essential for managing expectations while recovering endangered species. 

Yosemite Restoration I