California Begins Study on Black-tail Deer Decline

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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 Department of Fish and Game (DFG), the University of California, Davis and several doctoral candidates recently 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.

"We have concentrated our study in Mendocino County to try to find out if and why Black-tailed deer populations have declined in some of the state's best habitat," said DFG Associate Wildlife Biologist David Casady, "This study should provide important information for wildlife and habitat managers to better understand the factors involved in the deer population cycles and management alternatives."

The study will take place over the next three years in the rugged mountains east of Covelo, California in Mendocino, Glenn and Lake counties. The location was selected because it represents some of 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 and housing developments.

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 and employs state-of-the-art equipment. 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 additional mountain lions will be collared and followed during the study. Deer are mountain lions main food item. By tracking mountain lions biologists hope to estimate the overall level of predation on deer by lions in the study area. 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 such as coyotes to better understand habitat use and causes of deer mortality.

Scientists will carefully analyze changes in plant communities which may affect food availability over the life cycle of deer, major land or forest practices affecting habitat types and predation by mountain lions, coyotes and other predators.

UC Davis is responsible for study design, data collection and analysis. DFG is responsible for animal capture and handling, project oversight and providing vital equipment and personnel, as well as other expertise. UC Davis Adjunct Professor Heiko Wittmer will play a key role in the study (Wittmer can be contacted at huwittmer@ucdavis.edu).

Major funding for the study comes from The California Deer Association (CDA), UC Davis and DFG. Other donors include the Mendocino County Blacktail Association.

"Black-tailed deer are very important to California hunters and there are a lot of questions regarding why they declined. Hopefully this study will provide some answers," said Jim Lidberg, Project Chairman for the CDA. "We look forward to working with DFG and improving the herds in the future."