The author was among the first to investigate the potential for a linkage between the Greater Yellowstone and Northern Continental Divide Ecosystem grizzly bear populations. A map of the possible linkage is shown, depicting the following areas (north to south): McDonald-Rogers Pass, Elkhorn Mountains, Champion-Thunderbolt, Highland Mountains, Tobacco Root Mountains, Snowcrest Mountains, Gravelly Mountains.

"The [Glacier and Yellowstone] areas… are linked by mountainous country in primitive or semiprimitive condition. The [Grizzly Bear] Recovery Plan does not encompass management of this intervening habitat and thus its possible role in future grizzly bear management has not been provided for. As interest in grizzly bears has grown, increasing numbers of reports outside the 2 recognized population blocks have come to me. Although many could not be verified, some are undeniable." (7)

"The bridge area is separated into blocks by highway corridors and intermountain valleys. These probably do not permit entirely free movement, but they probably do not represent absolute barriers. Interstate highways I-90 and I-15 are the most substantial of the highway barriers. Both have substantial contiguous cover in some areas, which could facilitate crossing. The daily movements observed for grizzly bears are adequate to cross any of the valley areas (Craighead 1980). A radio-equipped grizzly bear is known to have crossed the several kilometers of sagebrush-grassland habitat and well-traveled U.S. highway 287 in the Madison River valley when moving back and forth between Yellowstone Park and the Gravelly Range." (9)

Conclusions
"The exploratory hypothesis presented here differs from the views expressed in the Grizzly Bear Recovery Plan (U.S. Dep. Int. 1981). The recovery plan absolves the Helena, Deer Lodge, and Beaverhead national forests and industry from considering the grizzly bear in their management plans and impact statements involving these bridge units. I suggest that the grizzly bear observations from these areas should not be dismissed as "accidental" and that the potential for a filter bridge connecting the 2 populations exists. Failure to consider it will result in unnecessary degradation of a biologically important block of habitat… Maintenance of such a bridge would substantially improve the long-term survival probability of the grizzly bear. It would also enhance the survival of the Yellowstone population. A system to gather and verify reports on grizzly bear activity should be established for these areas. Management consideration should encompass the maintenance of bear habitat continuity through these mountain ranges. Future studies should determine the degree of genetic isolation of the Yellowstone grizzly bear population." (9)

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