Moose, the largest member of the deer family, were reportedly very rare in northwest Wyoming when Yellowstone National Park was established in 1872. Subsequent protection from hunting and wolf control programs may have contributed to increased numbers but suppression of forest fires probably was the most important factor, since moose here depend on mature fir forests for winter survival.
Moose breed from early September to November and one to three calves are born in May or June. Calves weigh 25 to 35 pounds at birth but grow rapidly; adult females (cows) weigh up to 800 pounds and males (bulls) up to 1300 pounds. Bulls are readily identified by their large, palmate antlers, which are shed annually, and their bells, an apparently useless dewlap of skin and hair that dangles from the throat. Moose live mostly solitary lives, and die from disease, starvation, or predation by wolves and, occasionally, by grizzly bears.
Research on radio-collared moose in northern Yellowstone has shown that when snow depth forces moose from low-elevation willow stands in November, they move up to as high as 8500 feet, to winter in mature stands of subalpine fir and Douglas-fir. They browse fir almost exclusively during the deep-snow winter months. It was found that moose ate 39.6 percent subalpine fir, 25.5 percent willows, 10.6 percent lodgepole pine, 4.6 percent gooseberry, and 4 percent buffaloberry. Snow is not as deep under a canopy of conifer branches since some snow remains on them, and a crust that may restrict moose movements is less likely to form on shaded snow. However, it was found that moose could winter in areas where snow considerably deeper than that which elk could withstand.
Moose are commonly observed in the park's southwestern corner along the Bechler and Falls rivers, in the riparian zones around Yellowstone Lake, in the Soda Butte Creek, Pelican Creek, Lewis River, and Gallatin river drainages, and in the Willow Park area between Mammoth and Norris.