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California study focuses on black-tailed deer decline

From the California Department of Fish and Game

-- A new study is under way to determine why black-tailed deer populations in some areas of northern California have declined over the past 20 years.

The DFG, University of California-Davis and several doctoral candidates have began a three-year study of habitat changes, predation and land use patterns affecting black-tailed deer in Mendocino County. The decline in the harvest of black-tailed deer over the past 20 years is well-documented.

The study will take place over the next three years in Mendocino, Glenn and Lake counties. The location represents the best black-tailed deer habitat in the state and has seen a steady decline in the harvest of bucks. While some ranching and ownership patterns have changed over the past 20 years, most of the area is not directly affected by urbanization.

In 2009, an estimated 164,753 hunters pursued deer in California. Approximately 38,037 of those hunted in the B zone area encompassed in the black-tailed deer study. Statewide, the harvest of black-tailed deer bucks has declined from 27,846 in 1989 to 14,895 in 2009, a drop of 46 percent. In the counties in the study area zone, harvest numbers have dropped from 3,013 to 1,297, a 57 percent decline. 

The project takes a multi-species approach. Researchers are currently tracking fawns and adult doe deer with radio and GPS tracking collars. Additionally, a female mountain lion was fitted with an Argos satellite GPS collar in June and her movements are tracked daily. Five more mountain lions will be collared and followed during the study. Deer are mountain lions' main food source. By tracking them, biologists hope to estimate the level of predation on deer.

Deer with radio collars that die are necropsied within 24 hours to determine the cause of death. Remote cameras are being used to determine relative abundances of other species to better understand habitat use and causes of deer mortality.

Scientists will also analyze changes in plant communities which may affect food availability and major land or forest practices affecting habitat.

UC Davis will be responsible for study design, data collection and analyses. DFG will be responsible for animal capture and handling, project oversight and providing vital equipment and personnel, as well as other expertise. Major funding for the study comes from The California Deer Association, UC Davis and DFG. Other donors include the Mendocino County Blacktail Association.

"Black-tailed deer are important to California hunters, and there are a lot of questions regarding why they declined. Hopefully, this study will provide some answers," according to Jim Lidberg, Project Chairman for the CDA.

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