Grizzly subsistence relies mostly on 4 Food items -Trout, Pine Nuts, Moths & Ungulates.

More Trout Information

Grizzlies need the Yellowstone Cutthroat Trout

Presently, illegal introduction of exotic lake trout in Yellowstone Lake threaten the indigenous population of cutthroat trout that many bears feast upon during the spring spawn. The lake trout, which out-compete the cutthroat, live to deeply in the water to be a replacement food source for most bird and mammal species . In addition to the Grizzly many other animals depend on the Cutthroat trout including otters, eagles, kingfishers and ospreys. (Schullery, 1996)

Grizzlies and Whitebark Pine nuts

Whitebark Pine nuts are a high-nutrition food that many grizzlies seek out in the autumn before their winter slumber. Unfortunately, this food source had declined by 25% in Yellowstone Park after the 1988 Yellowstone forest fires. And even though whitebark pine may reestablish on sites burned by fire, production of a substantial number of cones is not expected for a century (Matson and Reinhart, 1994). Whitebark Pines are also threatened by the emergence of an arboreal disease known as blister rust. This alien fungus has destroyed whitebark pine stands in northwest Montana and is now infecting more and more trees in the Yellowstone region (Matson and Pease, 1999)..

The Red Squirrel provide nut caches for bears

Most whitebark pine cone crops are dependent on the harvesting by red squirrels who cut the cones down and bury them in mounds of forest litter called middens, or a cache. Because whitebark pine cones do not fall off the tree or drop their seeds the year they ripen and grizzly bears cannot climb trees, grizzlies must rob squirrel middens to feed on the seeds (Matson and Reinhart, 1997).

Clark's Nutcrackers are important!

These birds play a central role in the dispersal of Whitebark Pine (Hutchins and Lanner 1983). Thanks to the Johnny Appleseed-like habits, new whitebark pines can eventually grow from the thousands of seeds these birds bury and leave behind. Unfortunately, the spread of blister rust is threatening the Yellowstone Whitebark and it is feared that the nutcracker will not stick around as nut crops fail. Instead they will move to lower elevations where the smaller seeds of other pines can support them, but in fewer numbers. Fewer birds to disperse seeds means less regrowth in high-elevation clearings, a lowered tree line, and ultimately less food and habitat for nutcrackers, squirrels, and bears (Baskin 1998).

More Whitebark Pine Information

The critical role of whitebark pine!  

Following bumper whitebark cone crop years, pine nuts can dominate the food habits of bears for the entire next year. Both grizzlies and black bears alike eat whitebark pine seeds whenever they are available. In average crop years, bears feed on them from mid-August too late fall. Following years of bumper crops, many cones remain in squirrel caches the nest spring. When this happens, bears begin to feed on pine nuts as soon as they emerge from their winter dens and are capable of locating and excavating cone caches under at least 6 feet of snow(Kendall, 1983). Unfortunately, researchers have estimated that during poor whitebark pine nut production, grizzly bear deaths have increased by nearly 50% as bears leave the mountains for populated areas in search of supplemental food (Mattson & Reinhart 1997). In addition, besides the loss of trees from the growing blister rust epidemic, studies also suggest that global climate change may shrink the habitat available for whitebark pine and it is feared that virtually all-available whitebark habitat could be lost within Yellowstone.

More Moth Information

Yellowstone Grizzlies will gorge on Army Cutworm Moths

Recent bear research documented that bears in the Greater Yellowstone and Glacier Ecosystems feed on army cutworm moths. From entomological studies, it was known that these moths migrate in early summer form the Great Plains to spend the summer in the Rocky Mountains.. In Yellowstone NP, army cutworm moths spend their days resting in the cool spaces between jumbled rocks in talus fields near the tops of some of Yellowstone’s highest peaks. The moths emerge at night to feed on nearby flower nectar. Research on bear use of moths and the alpine ecology of army cutworm moths estimated the nutritional importance of this diet item; during peak feeding periods when moths are abundant, bears eat approx. 40,000 moths/day. This high nutrition food lures bears into the relative safety of the high country, miles from the nearest humans. These insects, however, are vulnerable to pesticide spraying in the valleys below, as well as to the loss to global warming of their own tundra food sources – wildflower nectar. In addition, grizzlies feeding on moths are disturbed by recreational mountain climbing -

Link to recreation site containing more on the disruption of moth feeding

Grizzly dependence on ungulates:

Studies by Mattson and Charles Robbins at Washington State University show that Yellowstone grizzlies represent one of the most meat-dependant bear populations in North America. Carcasses of winter-killed bison and elk have been an important source of protein for grizzlies just emerging from their dens in the spring. But those carcasses could become fewer as the government reduces and tightly regulates park bison and free-ranging elk herds to reduce the possibility of wildlife spreading the disease known as brucellosis to domestic cattle outside the park. Agencies are even discussing management schemes for bison that would cap their numbers at about half of what they were during the late 1980’s and early 1990’s

More Wolf information

Wolves, Ungulates and Grizzly interactions

According to researchers in the Yellowstone region - who after wolf reintroduction are gaining new insights into carnivore roles - wolves are good engineers of biodiversity and most meat eaters actually gain from having them around (cougars and coyotes being the exception). Wolf kills can mean more food for grizzlies (and eagles, ravens and other scavengers). Some researchers witnessing new grizzly- wolf interactions are not quite ready to say that wolves benefit grizzlies but believe at the very worst the grizzly is neither helped nor harmed. For example, sometimes bears chase wolves off kills and other times wolves chase grizzlies, and deaths have occured on both sides." See link "When carnivores clash " for more information.