Grizzly Bear
Grizzly bear need between 50 and 500 square miles for home range. Quite often, roads and highways cut through this home range, fragmenting prime habitat and creating hazardous obstacles for migrating bears.
More importantly to bears, roads mean the disturbance of traffic and increased human activity and less of the natural habitat they need for their daily, annual and life cycles. Loss and degradation of habitat displaces bears, increasing the risks to survival of the populations. Roads also increase access for both legal and illegal hunters, a major source of bear mortalities.
Numerous studies have shown that roads, and the increased access and disturbance they bring have a significant impact on the grizzly bear.
- After monitoring collared bears from 1983 to 1988, researchers found that bears avoided high quality habitat near roads and trails. The distance from seasonally closed roads increased significantly when the road was reopened. The study concludes, "Grizzly bear avoidance of high quality habitat near roads and trails may lessen the opportunity for individuals to obtain food and increase intraspecific competition by further forcing bears into limited remote habitat." Road and Trail Influences on Grizzly Bears and Black Bears in Northwest Montana, by Manley Kasworm.
- Bears in Yellowstone National Park avoided habitat within 3 km of developments, and within 2 to 4 km of roads. Grizzly orient towards highly productive habitat, and away from other bears and human activity. Because they are displaced toward humans by adult males, adult females are most affected by roads and developments, which are manifest in both higher mortality risks, and lower fecundity. The Effects of Development and Primary Roads on Grizzly Bears in Yellowstone National Park, by D.J. Mattson.
- Grizzlies were monitored near Glacier Park from 1979 to 1985. Eleven bears were known to have been shot in the study area; only one is known to have been killed away from a road. In a later study of that same area, bears were found to use habitat within 100 m of a road less than expected, and that avoidance of roads was independent of traffic volume; even a few vehicles were sufficient to displace bears. Behavior of Grizzly Bears in Response to Roads, Seismic Activity and People, by Mace McLellan.
Problem Roads
- US Highway 2 - between East Glacier and West Glacier, Montana
- US Highway 89, 49 and 17 - between East Glacier, Montana and the Canadian border
- The Trans Canada Highway through Banff National Park in Alberta and associated areas on the Trans Canada in British Columbia
Source: Fragmentation Effects of High-Speed Highways on Grizzly Bear Populations Shared Between the United States and Canada, by Chris Serveen, 1998.
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