GRIZZLY BEAR (Ursus arctos horribilis)
Grizzly bears are BLUE-listed and classed as VULNERABLE in B.C. by COSEWIC and are considered EXTIRPATED in the prairies (part of Alberta, Saskatchewan and Manitoba). They are considered threatened where they still occur in the Southern Interior Ecoprovince. In addition, four cross-border populations are classed as THREATENED under the U.S. Endangered Species Act: the North Cascades, Selkirks, Cabinet-Yaak and Northern Continental Divide Grizzly Bear Ecosystems.
The provincial population estimate for grizzly bears is 10 000-13 000. Local population declines are occurring in many areas of the province, due primarily to area concentrated mortality, habitat loss and fragmentation. Sources of area-concentrated mortality include hunting, poaching for gall bladders and other body parts, and inadequate garbage management. These activities are associated with increased access stemming from forestry, mining, and oil and gas development, and represent a particularly significant threat when adult females are taken. Habitat loss and fragmentation occur on a broad scale as a result of forestry and fire suppression, and expanding human settlement. The latter, with its associated developments (agriculture, recreation, roads, hydro reservoirs and utility corridors) is concentrated in valley bottoms formerly used as spring habitats and movement corridors between mountain ranges; human population increase represents the greatest threat to grizzly bears in B.C. Unfortunately, several major protected areas contain poor quality grizzly habitat, and are inadequate to maintain viable populations of the species.
Grizzly bears in B.C. have a wide range of life-history strategies to meet their nutritional, security, thermal, reproductive and "space" requirements. Body and home range sizes across the province are proportionate to food quality, quantity and distribution, and the length of the denning period. Home range sizes also vary by sex and age class; adult males vary from as little as 350 km2 on the coast to over 2500 km2 in the northern interior. Adult female home ranges may be as small as 25 km2 in productive habitats. In B.C., grizzly bears are efficient predators and scavengers but rely more on a vegetative diet. A huge variety of plant, animal, fish and insect food sources are regionally important.
Reproductive rate is the lowest recorded among North American land mammals. First age of reproduction varies from age 4 upwards, cubs per litter from 1 to 4 (1.4-2.5 average), and litter interval is usually 3 years (cubs, born in winter dens, remain with their mothers until they are
26-28 months old). Population densities vary from approximately 5 up to 65 bears per 1000 km2 with high seasonal variance (e.g., congregation on a salmon spawning channel). Adult female grizzly bears will tolerate their female offspring within their home ranges, especially when population densities are lower than the habitat can support. As a result, subadult female dispersal outside maternal home ranges is rare in much of B.C. Areas where all resident adult females have been killed are therefore not usually recolonized by dispersing subadult females. Transient males may continue to use such areas, but long-term local viability is unlikely.
Grizzly bears historically occurred throughout B.C., with the exception of some coastal islands (e.g., Vancouver Island, the Queen Charlotte Islands, and others). They have been extirpated from much of south and south-central B.C. (e.g., lower elevations of the Okanagan, the lower mainland, and parts of the Cariboo), and population viability is in jeopardy in the Southern Interior Ecoprovince. The following are ecosections within which grizzly bears have been extirpated:
COM: NWC, SPR (part), EPR (part)
GED: GEL, FRL
CEI: FRB, CAB
SOI: SOB, SOH, OKR, NOB, NOH (part), NTU (part), STU, THB
The extreme southeast corner of the province appears to support a healthy population of grizzly bears, as do the Northern Boreal Mountains ecoprovince and the northern portion of the Sub-boreal Interior ecoprovince. Elsewhere in the province, distribution is highly variable. Population density is typically lowest near human settlement, areas with high human access and near agricultural activity unless abundant, high quality attractants are available (e.g., dumps). Figure 1 shows current grizzly bear habitat potential throughout B.C.
AT, BWBS, CWH, ESSF, ICH, IDF, MH, MS, PP, SBPS, SBS, SWB
Grizzly bears in B.C. have such an enormous range of behavioural adaptations to diverse regional ecosystems that generalization about habitat requirements is difficult. Even within a region, individual bears may have vastly different approaches to meeting their requirements. Some bears - particularly males, adopt a highly mobile, seasonally "transient" strategy, whereas other bears are more "resident." Some bears rely more heavily on predation than others, and some use "high elevation" annual home ranges as opposed to migrating to lower elevations on a seasonal basis. Strategies are somewhat flexible; individuals adapt to annual variation in food supply and can learn to exploit newly available food sources. However, many of a grizzly bear's movements, habitat selection and foraging patterns are learned as a cub and are reinforced throughout their lives (20-30 years). Home range fidelity may be strong as a result, especially for females.
Although meeting nutritional requirements is the primary factor in habitat choice, selection is also based on thermal cover (e.g., dens/bedding sites), security (e.g., females protecting cubs), or access to potential mates during the breeding season. Habitat selection is also strongly influenced by intra-specific (social) interactions and the presence and activities of people.
Grizzly bear habitat requirements must be viewed at several spatial scales. Transients deliberately travel to specific landscapes in a subregion on a seasonal basis. Both residents and transients select specific patches of habitat or complexes of habitats within landscapes. Within patches they may only require specific food-producing microsites. Habitat requirements must also be viewed at various temporal scales; continually shifting seasonal food supplies, annual food variance (e.g., berry crop failure), and long term influences on habitat quality such as fire suppression must all be considered. Concurrent attention must be given to meeting the spatial requirements of individuals within and across landscapes and examining population-level habitat supply.
Figure 1. Current grizzly bear habitat potential throughout British Columbia.
(source:A.N. Hamilton, D.A. Dermarchi, D. Leblanc, K.Karr, May 1997.)
Because grizzly bears are naturally found at low densities, it has been estimated that 20 000 to 50 000 km2 of occupied and connected habitat is required to ensure their long term viability. To sustain habitat supply for populations, individuals must be able to move freely among valued habitats, without being restricted by human-caused blockages or being attracted to mortality sinks around human settlements.
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