Animal Field Guide

Grizzly Bear

Ursus arctos horribilis
(Ursidae)

Global Rank: G4T3T4
State Rank: S2S3

Agency Status
USFWS: LT
USFS: THREATENED
BLM: SPECIAL STATUS

Grizzly bears have a massive head with a prominent nose, rounded inconspicuous ears, small eyes, short tail and a large, powerful body (Pasitschnaik-Arts 1993). The facial profile is concave and there is a noticeable hump above the shoulders. The claws on the front feet of adults are about 4 inches long and slightly curved. Grizzly bears range widely in color and size. The most prevalent coloration of bears in Montana is medium to dark brown underfur, brown legs, hump and underparts, with light to medium grizzling on the head and back and a light patch behind the front legs. Other forms, lighter or darker with varying levels of grizzled hair patches, occur in lesser numbers. Although extremely variable depending on the season, adults are around 185 centimeters long (Foresman 2001) and weigh around 200 kilograms in males and 130 kilograms in females (Kasworm and Manley 1988).

Adult grizzly bears differ from black bears (Ursus americanus) in being larger and by having a hump above the shoulders, a concave (rather than straight or convex) facial profile, shorter and more rounded ears, a rump lower than the shoulder hump, and longer, less curved claws usually evident in the tracks. Identification can be difficult at times and Montana Fish, Wildlife and Parks has developed an online test to help people better distinguish between black bears and grizzly bears. This test can be accessed online at: www.fwp.state.mt.us/bearid/

No true migration occurs, although grizzly bears often exhibit discrete elevational movements from spring to fall, following seasonal food availability (LeFranc et al. 1987). They are generally at lower elevations in spring and higher elevations in mid-summer and winter.

In Montana, grizzlies primarily use meadows, seeps, riparian zones, mixed shrub fields, closed timber, open timber, sidehill parks, snow chutes, and alpine slabrock habitats. Habitat use is highly variable between areas, seasons, local populations, and individuals (Servheen 1983, Craighead 1982, Aune 1984). Historically, the grizzly was primarily a plains species occurring in higher densities throughout most of eastern Montana.

Grizzly bears are opportunistic and adaptable omnivores. Grizzly bears have a large vegetative component (more than half) to their diet and have evolved longer claws for digging and larger molar surface area to better exploit vegetative food sources. Grizzlies feed on carrion, fish (Yellowstone cutthroat trout are a large seasonal component of the diet for Yellowstone grizzly bears), large and small mammals, insects, fruit, grasses, bark, roots, mushrooms, and garbage. They often cache food and guard it. In the Yellowstone region, ungulate remains and rodents were a major portion of early season scats; grasses, sedges and herbs dominated in May and June, with whitebark pine seeds, fish and berries most prevalent in late season scats when bears become hyperphagic (Mattson et al. 1991). Whitebark pine seeds appear to be so important to grizzlies that there is a correlation between grizzly bears killed in control actions and the success of the whitebark pine crop. More fatalities have been recorded during poor crop years when grizzlies forage at lower elevations and come into contact with humans more often. Grizzly bears often feed on insect aggregations (e.g., army cutworm moths, ladybird beetles). In the Yellowstone ecosystem, alpine insect aggregations are an important source of food, especially in the absence of high-quality foraging alternatives in July and August of most years (Mattson et al. 1991). Grizzly bears have been known to kill and consume black bears (Gunther et al. 2002).

Grizzlies are known to feed on a wide variety of plants (36 to 74 species) in Montana. Food habits vary locally, seaonally and individually. Generally, grizzlies feed on graminoids, forbs, rodents and carrion in spring. In summer, they feed on forbs, fruit, horsetails, insects, and roots; in fall, berries and pinenuts predominate (Craighead 1982, Servheen 1983, Aune 1984). Yellow sweetvetch is an important food with wide distribution (Edge, Marcum, and Olson-Edge 1990).

Annual home ranges in the Swan Mountains, Montana, averaged 768 square kilometers for males and 125 square kilometers for females; adult home ranges were larger than those for subadults. Spatial and temporal factors affected home range size (Mace and Waller 1997). Two studies examined grizzly responses to resource development (A84AUN01, A83MCC01). Cannibalism has been reported (Mattson et al. 1992).

Grizzly bears exhibit a long life span, late sexual maturity and protracted reproductive cycles (Craighead et al. 1976). They are polygamous and several males may fight over an estrus female. In Montana, grizzly bears breed in late April through late June or early July (Aune 1985). Implantation of the fertilized egg is delayed until late autumn when the embryo implants into the uterus. Around two months after implantation, 1 to 4 (average 2.8 in Montana) young are born in the winter den. They are helpless at birth and weigh around 500 grams. Growth is rapid and young are nursed for the first 1.5 to 2.5 years (Foresman 2001). The young remain with their mother through the next two winters. Young usually obtain adult size in 4 to 6 years. Females generally breed every 2 to 4 years. Females first breed when they are 4.5 to 5.5 years old and males gain sexual maturity at the age of four and half years. A few live as long as 20 to 25 years.

Current grizzly bear management throughout their range in Montana is dictated by their threatened listing under the Endangered Species Act (ESA). Under the ESA, no federal actions can cause further endangerment of grizzly bears. Federal land management agencies such as the U.S. Forest Service and the Bureau of Land Management must conduct management actions on their lands so that grizzly bears are not jeopardized. Interagency grizzly bear management guidelines have been developed for these managed lands. In addition, the state of Montana has a Grizzly Bear Policy (MCA 12.9.103) that outlines policy guidelines for Montana Fish, Wildlife and Parks to promote the conservation of grizzly bears in Montana. Other regionally specific management plans include the Grizzly Bear Management Plan for Southwestern Montana 2002-2012 (Montana Fish, Wildlife and Parks 2002), and various tribal, National Forest, and National Park plans and policies. Most of these management plans are centered on three major themes: management of habitat to ensure grizzly bears have large expanses of suitable interconnected lands in which to exist (see Habitat and Food sections above), management of grizzly/human interactions that most often result in death for the bears (and sometimes humans) involved (this is a particularly important concern for female bears because their removal may have significant impacts on the demography of isolated populations), and research to determine the population size and trends to ensure that grizzly bear populations are not being jeopardized. Please consult any of the management plans listed above for grizzly bear management specifics.