Wyoming

Brown bear populations in the lower 48 states have been greatly reduced in numbers and their habitat has been fragmented by human development.

There are three major large 'islands' of bear habitat in the United States and adjacent Canada. These have been designated as the Northern Continental Divide Ecosystem (NCDE on map), Bitterroot (or Salmon-Selway) Ecosystem (SSE on map), and Yellowstone Grizzly Bear Ecosystem (or Greater Yellowstone Ecosystem; GYE on map) Recovery Zones by the U.S. Fish and Wildlife Service (USFWS 1993).

The cores of these areas are protected as National Parks (in both the U.S. and Canada) and Wilderness Areas. Additional lands around these cores are designated as grizzly bear recovery areas where maintaining viable grizzly bear populations is a management priority. Surrounding the recovery zones are some National Forest lands. Much of the National Forests are at present undeveloped. Some areas contain grizzly bear habitat and may support a few bears, other areas are only occasionally visited by grizzly bears.

Smaller islands of habitat exist, largely in Canada but extending over the U.S. border in the Cabinet Yaak Ecosystem (CYE), and Selkirk Mountains Ecosystem (SE).

These areas of habitat have been designated as Recovery Zones by the U.S. Fish and Wildlife Service. They have been determined to be sufficient to support a minimum brown bear population size recovery goal) deemed large enough to be self sustaining (USFWS 1993).

Between the three large 'islands' there are small 'stepping stones' of habitat that could possibly serve as corridors for movement.

Current best estimates for grizzly bears in the Greater Yellowstone Ecosystem are about 627 total bears. The population appears to have been increasing slightly for the past several years. These data have been collected by the Interagency Grizzly Bear Study Team (IGBST) and are reported in the 1999 research report. Current research reports are available at that web site.

In 1993 it was estimated that in the GYE there were at least 236 bears (67 adult females) The recovery target is 15 females with cubs per year; a density of about 11.2 bears per 1000 square kilometers (USFWS 1993). In 1994 there were 11 known mortalities in the Yellowstone Ecosystem (including 2 adult females and one subadult female). In 1995 there were 18 known mortalities (including 3 adult females, 3 subadult females, and one female cub).

In an older publication, Eberhard and Knight (J. Wildl. Manage. 60(2):416-421) derive a variety of population estimates for the YGBE: A population review committee in 1994 estimated a minimum total population of 245 grizzly bears. An estimate based on ages of all bears handled and identified gives an absolute minimum of 133 bears. An estimate using females in a Petersen Index with Chapman's bias corrected equation suggests a total population of 390 bears. An estimate from distinct family records yields 339 bears (for which the 90 percent confidence interval is 280 to 610 bears).

Analysis of genetic samples of 667 grizzlies, 72 of which were from Yellowstone, demonstrated a significantly lower H (55%) for Yellowstone grizzlies compared to a high of 78% in the Kluane sample (n=50) and a low of 26% in the Kodiak sample. Estimates of Ne ("genetic effective size" ) for the total Greater Yellowstone Ecosystem population are only 15-54 effective grizzly bears however (Paetkau D., L. Waits, L. Craighead, E. Vyse, R. Ward, and C. Strobeck. 1997. Dramatic variation in genetic diversity in brown bears across North America: implications for conservation. In Review, Cons. Bio.) .

Eberhard and Knight's current estimates show a 2 to 5 percent increase. Other researchers (Mattson and Pease, 10th IBA proceedings, in press) question these findings.

In 1996 approximately 33 "unduplicated females with cubs" were observed with a total of 70 cubs-of-the-year in the Greater Yellowstone Ecosystem. This is an historic high. The most females with cubs seen before were 25 in 1986, and the most cubs seen before were 57 in 1990. The high reproduction in 1996 may be a consequence of the low reproduction in 1995 when only 16 females were seen with cubs.

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