Round Valley Mule Deer and their Migration Corridor
The Round Valley deer herd consists of approximately 3000 Rocky Mountain mule deer (Odocoileus hemionus ssp. hemionus). The California Department of Fish and Game has an active program that performs annual regular surveys and counts of this herd. This herd migrates from its small winter range in Round Valley (northern Inyo County) up through the mid-elevations, and the one mile wide bottleneck in Swall Meadows, to the alpine meadows of the Central Sierra to give birth and to access good forage. The width of the migration corridor in Swall Meadows is limited by the steep cliffs of Wheeler Ridge to the west and the deep canyon of Lower Rock Creek Gorge to the east. Twice a year they traverse their migration corridor where they face mountain lions, cars, and increasing human presence.
Viable winter range habitat is critical for a migrating deer herd. In severe winters with heavy snow, the deer must have access to the lowest elevations where forage is still accessible and movement is not hampered by deep snow. The Round Valley deer herd has a relatively small winter range, compared with other mule deer herds throughout the west. Their winter range is only about 30 square miles while their summer range spreads out to about 1000 square miles.
Approximately 75% of the herd migrate north in the spring through Swall Meadows, around Wheeler Ridge in southern Mono County, turning west into Long Valley and up into the Mammoth area. Groups of deer will veer off the migration route and travel up canyons into the high Sierra. The other 25% migrate through the Buttermilk area up into the Bishop Creek drainage and over the high passes into the Central Sierra. The route is reversed in the autumn.
Mule deer mate in the winter, with the bucks dropping their antlers soon afterwards. In early spring their new antlers emerge covered with soft velvet and retaining the general structure from previous years. If healthy, the buck may add another point each year to his antlers. Many females are pregnant during the spring migration to the high Sierra and are very sensitive to stresses such as human disturbance, dogs, and noise. Does will have 1-2 offspring, which stay close to their mother through the fall migration to the winter range.
Sagebrush (Artemisia tridentata ssp. tridentata) and antelope bitterbrush (Purshia tridentata ssp. tridentata) are the main components of the plant communities that mule deer depend on for food and cover. Antelope bitterbrush, a beautiful evergreen shrub in the rose family, is especially important to deer in the fall when they return from the high elevations. The leaves and shoots provide significant quantities of calcium, phosphorus, fat and crude protein at a critical time of year for the deer. Deer also utilize the meadows, streams and willow thickets that are found in the migration corridor.
The main predator of the mule deer is the mountain lion (Puma concolor), which is found in healthy numbers in the Eastern Sierra. Lions depend on mule deer for 60-80% of their diet and are consequently very dependent on the continuing viability of the deer herd. A local researcher, Dr. Becky Pierce, has studied the mountain lion extensively and has found that, while the lion population fluctuates, there are usually two to four lions utilizing the habitats within the Round Valley deer herd migration corridor at any one time. They are secretive animals, generally avoiding contact with humans as long as an abundant food sources exists, such as the Round Valley deer herd.
Many other species are abundant in the migration corridor. The varied habitats support many species of birds: local experts have noted 137 species of birds in the Round Valley area. Some of the highlights from that bird list include yellow warbler, yellow-breasted chat, blue grosbeak, western and mountain bluebirds, and many species of raptors including bald eagle, golden eagle, northern harrier and many more. Another expert has surveyed 16 different bats including three Species of Special Concern: Townsend’s Big-eared Bat, Spotted Bat, and Pallid Bat.
Acknowledgements and Appreciations
The Eastern Sierra is fortunate to have many dedicated and talented biologists, botanists, and passionate observers focused on the amazingly diverse and interesting flora and fauna of our region. The ESLT offers a sincere thank you to the following people for sharing their knowledge: Alisa Ellsworth, Derham Giuliani, Anne Halford, Debbie House, Stephen Ingram, Tom Kucera, Jim and Debby Parker, Becky Pierce, Denyse Racine, Timothy Taylor, John Weyhausen, and Darrell Wong. ESLT takes full responsibility for any errors or misstatements.
All photos by Stephen Ingram, copyright protected