Mule Deer Migration - It's Tradition

September 12, 2005

Every fall when the days get shorter, temperatures are cooler, and the leaves have changed color, a pilgrimage begins. The journey has no designated routes, trails, or roads and can begin anywhere in the Boise Mountains. The journey starts for some at the foot of the Sawtooths near Atlanta while for others the journey begins near the old mines around Idaho City or farther south near Featherville or Rocky Bar. While maybe not as dramatic or long as the migration of salmon, waterfowl, or some other wildlife, every year over 20,000 mule deer migrate from their summer range in the Boise Mountains to their historical winter range in and around the Boise Foothills.

Good mule deer winter range has an abundance of healthy shrubs and grasses, areas of relief from deep snow accumulation, and a low level of human disturbance that can alter the habitat and cause deer to use more of their limited energy reserves trying to avoid people. Vegetation on the winter range in the Boise Foothills consists mainly of shrubs like bitterbrush and sagebrush and several different types of grass. There is less snow in the lower elevation foothills, particularly on the south and southwest facing slopes where it is warmer and the snow melts faster.

The Idaho Department of Fish and Game has conducted numerous studies on mule deer including projects where we captured and radio-marked deer to track their survival and dispersal from the Boise Front winter range. We radio-collared mule deer during the winter near Blacks Creek and at several sites on the Boise River Wildlife Management Area. Some of these studies started in 1993 and we continue our quest for knowledge with other research projects today. During these projects we have tracked hundreds of radio-collared deer to their summer locations which are spread throughout the Boise Mountains. Every fall this deer population, with an estimated number of 21,300 in 1998 to 27,800 in 2003, migrates back to the winter range in the Boise Foothills. Mule deer are traditionalists, and they come back to the same winter range year after year. The winter range is very small in comparison to the area they utilize in the summer but is critical to the survival of the deer that come there for food and shelter during the winter. The entire foothills winter range is important to deer, but during hard winters the lower elevation habitat becomes even more crucial to the mule deer's survival as they try to avoid the deep snows that hamper their abilities to find food and cause them to deplete their limited stores of energy at a faster rate as they try to move through the snow.

Impacts to the small area that makes up the winter range have cascading effects over a much broader area. In this case the area goes beyond Idaho City, Atlanta, and Anderson Ranch Reservoir. Mule deer are not ones to change their traditions. Radio collared deer have come back to winter range locations changed by fire or development and suffered the consequences of no longer having the critical habitat components they need to survive.

Healthy year round habitat is crucial to wildlife survival. Wildlife depend on specific habitat needs at different times of the year for food, for a place to have and rear their young, to escape from predators, and to avoid extreme weather and snow. Deer that do not survive the winter because they no longer have the habitat they need will not be there in the broader area they use during the rest of the year. The deer will not have just moved on, they will be gone.