Spawning cutthroat trout were a major source of energy and nutrients for grizzly bears living within range of Yellowstone Lake between the mid-1970s and late 1990s. The estimated percentage of the bear population that exploited this resource varied from 15-25%, depending on the time period, although few grizzlies still consume trout. Almost all of the exploitation of trout by grizzly bears occurred during the May-July spawning season along streams tributary to Yellowstone Lake; the bears involved in this use comprised the majority of those active within 12 km of the Lake year-round. At least within recent historical times, trends in use of trout by Yellowstone's grizzlies were driven by variations in the size of the Yellowstone Lake cutthroat trout population. Trout numbers were low during the 1940s-1960s because of heavy sport fishing, and at rock-bottom lows during the last 15 years or so because of the combined effects of climate change and predation by a non-native predator--lake trout--which was unintentionally introduced into Yellowstone Lake during the early 1990s.
Cutthroat trout (Oncorhynchus clarkii) are widespread in the interior western United States . This extensive distribution, coupled with the complex effects of volcanism and glaciation, has resulted in varying degrees of genetic isolation sustained over varying periods of time. The upshot is a number of different clades and subspecies. The subspecies found within the bulk of Yellowstone's grizzly bear range is the Yellowstone cutthroat trout (O. c. bouvieri). The map to the right shows the historical distribution of this subspecies (in blue), together with the boundary of Yellowstone National Park and the Primary Recovery Area for Yellowstone's grizzly bears. Despite extensive overlap between the distributions of trout and grizzly bears in this region, almost all use of trout by bears has been concentrated around Yellowstone Lake for reasons that are not altogether clear.
They will eat human food and garbage where they can get it.
The longer, less curved claws and larger shoulder muscle mass of the grizzly bear makes it better suited to dig plants from the soil, and rodents from their caches. Grizzly bear food consumption is influenced by annual and seasonal variations in available foods.
However, not all bears have access to whitebark pine nuts, and in the absence of this high-quality food, the bear’s omnivory lets them turn to different food sources. Fall foods also include pondweed root, sweet cicely root, grasses and sedges, bistort, yampa, strawberry, globe huckleberry, grouse whortleberry, buffaloberry, clover, horsetail, dandelion, ungulates (including carcasses), ants, false truffles, and army cutworm moths.
Grizzly bears may range over hundreds of square miles, and the potential for conflicts with human activities, especially when human food is present, makes the presence of a viable grizzly population a continuing challenge for its human neighbors in the Greater Yellowstone Ecosystem. Numbers in Yellowstone.
The grizzly bear’s color varies from blond to black, often with pale-tipped guard hairs. In the Greater Yellowstone Ecosystem, many grizzly bears have a light-brown girth band. However, the coloration of black and grizzly bears is so variable that it is not a reliable means of distinguishing the two species.
May live 15–30 years. Grizzly bears are generally 11⁄2 to 2 times larger than black bear s of the same sex and age class within the same geographic region, and they have longer, more curved claws.
Bears emerge from their dens when temperatures warm up and food is available in the form of winterkilled ungulates or early spring vegetation. Greater Yellowstone grizzly bears begin to emerge from their den in early February, and most bears have left their dens by early May. Males are likely to emerge before females.