Moose Information Continued
Both sexes are dark brown, often with tan legs and muzzle. Bulls can be distinguished from cows by their antlers. Adults of both sexes have "bells"—a pendulous dewlap of skin and hair that dangles from the throat and has no known function.
In summer, moose eat aquatic plants like water lilies, duckweed, and burweed. But the principle staples of the moose diet are the leaves and twigs of the willow, followed by other woody browse species such as gooseberry and buffaloberry. An adult moose consumes approximately 10–12 pounds of food per day in the winter and approximately 22–26 pounds of food per day in the summer.
Some moose that summer in the park migrate in winter to lower elevations west and south of Yellowstone where willow remains exposed above the snow. But many moose move to higher elevations (as high as 8,500 feet) to winter in mature stands of subalpine fir and Douglas-fir. Moose can also move easily in these thick fir stands because the branches prevent snow from accumulating on the ground.
Moose are solitary creatures for most of the year, except during the mating season or rut. During the rut, both bulls and cows are vocal: the cows may be heard grunting in search of a mate, and bulls challenge one another with low croaks before clashing with their antlers. The weaker animal usually gives up before any serious damage is done; occasionally the opponent's antlers inflict a mortal wound.
Bulls usually shed their antlers in late November or December, although young bulls may retain their antlers as late as March. Shedding their heavy antlers helps them conserve energy and promotes easier winter survival. In April or May, bulls begin to grow new antlers. Small bumps on each side of the forehead start to swell, then enlarge until they are knobs covered with a black fuzz (called velvet) and fed by blood that flows through a network of veins. Finally the knobs change into antlers and grow until August. The antlers are flat and palmate (shaped like a hand). Yearlings grow six to eight inch spikes; prime adult bulls usually grow the largest antlers—as wide as five feet from tip to tip. Then the bull rubs and polishes his antlers on small trees in preparation for the rut.
Cows are pregnant through the winter; gestation is approximately eight months. When ready to give birth, the cow drives off any previous year's offspring that may have wintered with her and seeks out a thicket to give birth in.
Moose appear to have been scarce in Yellowstone until the latter half of the 1800s and in Jackson Hole until early in the 1900s. Forest fire suppression, restrictions on moose hunting, and moose transplantations contributed to their subsequent range expansion and increased numbers.
Forest fire suppression was probably the most important factor in their population increase because moose in Greater Yellowstone depend on mature fir forests for winter survival, unlike other North American moose populations that prefer shrubland that has been disturbed by events like fires.
The moose population declined following the fires of 1988 that burned mature fir forests. Many old moose died during the winter of 1988–89, probably as a combined result of the loss of good moose forage and a harsh winter. Unlike moose habitat elsewhere, northern Yellowstone does not have woody browse species that will come in quickly after a fire and extend above the snowpack to provide winter food. Therefore, the overall effect of the fires was probably detrimental to moose populations.
Although some Rocky Mountain moose populations have continued to grow and spread into new habitat, those in Yellowstone have declined since the 1980s. Estimated at roughly 1,000 in the 1970s, the current Yellowstone moose population is believed to be less than 200, with the northern range population down by at least 75 percent since the 1980s. Predation of moose calves by bear and wolf populations may be continuing to limit population growth, but the low pregnancy rates of Greater Yellowstone moose suggest limits set by food availability. Longterm studies suggest that North American moose populations tend to erupt, crash, and then stabilize for awhile at a density that depends on current ecological conditions and hunting pressure.
The state of Montana has limited moose hunting in the districts immediately north of Yellowstone to antlered bulls since 1996 and reduced permits to 15 a year. Eight bulls were harvested in 2008, when Montana Fish, Wildlife and Parks estimated that the population in those districts was 150.
Today, moose are most likely seen in the park's southwestern corner and in the Soda Butte Creek, Pelican Creek, Lewis River, and Gallatin River drainages.
Did You Know?
Lake trout are an invasive species of fish that is decimating the native cutthroat trout population in Yellowstone Lake.