Black bears may be the least carnivorous of the "carnivores" of North America. They consume a wide variety of seasonally abundant herbs, forbs, fruits, berries, nuts, and other plant parts and products. The specific plants may differ among the a number of ecoregions of North America. However, certain trends are evident. Spring foods are predominantly grasses, sedges, shoots and other high-protein lush green vegetation. Deer and other carcasses may be scavenged, as well as leftover nuts. Skunk cabbage is important in Massachusetts and squaw root in the southern Appalachians. During summer, bears shift to energy-rich "soft mast" foods such as huckleberries, blackberries, raspberries, grapes, and cherries. Protein-rich insects such as ants, wasps, and beetle larvae are usually taken.
Crayfish, frogs, birds' eggs, mice, red squirrels, woodchucks, snowshoe hare, and other animal food are occasionally eaten. Then, in autumn (where available), "hard mast" items including acorns, hickory nuts, beechnuts, hazelnuts, pine nuts, and similar foods are taken. Corn is also eaten where available. Bears can make tremendous weight gains in fall, as much as 3 to 4 lbs. per day. However, in northern areas, where hard mast is lacking, bears must rely only on berry crops for weight gain and den after those are exhausted. Bears, especially adult males, and especially when foods are scarce, may travel up to 125 miles outside their home range in late summer and early fall to a concentrated food source before returning home to den. A number of historical accounts from Louisiana, Minnesota, New England, Ontario, Wisconsin, and elsewhere mention these "migrations" or "forays", which often followed well-defined trails beaten down over time.
In spring and early summer, poplar catkins, leaves, and lush grasses are common foods. Bears lack a caecum and do not have any known ability to digest cellulose so the nutritional value of such foods is not apparent. However, researcher-habituated bears have been seen to relish deer scat and feed on the intestines of winter-killed deer. Perhaps by this means bears may acquire cellulose-digesting organisms which allow the bears to digest foods they could not otherwise utilize.
Several workers have suggested that the period between den emergence and the availability of summer-ripening fruits and berries is a "negative foraging period" during which bears gather enough food to sustain life, but not to gain weight. However, recent studies in Minnesota challenge this assumption. Young bears can and do gain weight from spring foods. However, lactating females may indeed lose weight due to the high energy demands of milk production. Breeding-age males may also lose weight due to changes in physiology and behavior.
Bears which feed in garbage dumps, campgrounds, or at bait stations may grow faster, attain greater weights, and have greater fertility than their wild counterparts. In the Great Smoky Mountains National Park, both male (224 lbs.) and female (132 lbs.) "panhandler" bears using high-energy human foods were heavier on average than wild bears of the same sex (163 and 110 lbs). Additionally, 56% of panhandler females were lactating, as opposed to 33% of wild sows. Similarly, in Michigan, "dump bears" tended to be heavier than those captured elsewhere, while garbage-fed females averaged 3.1 cubs per litter as compared to 2.0 elsewhere. One 9-yr-old male in northern Minnesota, fed daily at a bait station, grew from 410 to 620 lbs. over a 51-day period.
References: Beecham and Rohlman 1994, Bray and Barnes 1967, Cardoza 1976, Chi et al. 1998, Costello 1992, Eagle and Pelton 1983, Fair and Rogers 1990, Herrero 2002, Kilham and Gray 2002, Kolenosky and Strathearn 1987a, McDonald and Fuller 1994, McLean and Pelton 1990, Noyce 1994, Noyce and Garshelis 1994, Powell et al. 1997, Rogers et al. 1976, Rogers 1976, Rogers and Wilker 1990, Schorger 1949, Seibert 1991, Spencer 1955, Tisch 1961, Warburton 1982.
Posted by: Kelly Source