New Reports on Grizzly Bear Distribution and Habitat Needs in the U.S. Northern Rockies Say Bears Won't Survive Unless Their Habitat Area is Increased Greatly

Three recently published papers conclude both the distribution and spatial needs of grizzly bears greatly exceed government recovery zones delineated for grizzly recovery in the U.S. northern Rockies. The reports, authored by Mike Bader of the Alliance for the Wild Rockies, propose an expanded habitat network to provide for grizzly bear viability.

"Distribution of Grizzly Bears in the U.S. Northern Rockies," published in Volume 74, Number 4 of the journal Northwest Science, shows that grizzly bears are currently distributed throughout an area much larger than the recovery area boundaries. Using a computer home range program, HOME RANGER, and about 3,000 digitized locations of grizzly bear observations, total distribution in the U.S. northern Rockies is estimated at about 102,524 km2 (about 40,000 square miles).

Grizzly bears significantly expanded their range in the Yellowstone area, particularly to the south and east of the recovery boundary near Jackson Hole, Wyoming and to the north in the Tobacco Root Mountains and other areas near Bozeman, Montana. Grizzlies also expanded their distribution east of the Northern Continental Divide recovery zone.

Current management allows more relaxed standards for habitat security and road densities between the recovery zones, which may deter grizzly bears from establishing ranges within potential linkage habitats. Major differences for grizzly bears residing beyond the recovery zones is that they receive no formal consideration by the U.S. Fish & Wildlife Service pursuant to Section 7 of the Endangered Species Act on projects which may adversely modify habitat and/or elevate mortality risk. Other differences may include no special food storage orders for backcountry users such as hunters or hikers and no restrictions on road density and cover standards specific to grizzly bears. Failure to document or account for grizzly bear presence may increase the chances of surprise encounters between bears and humans. Higher risks/rates of conflict may reduce human tolerance for grizzly bears and therefore increase mortality and overall risk to the species.

The recent expansion in distribution area does not necessarily imply that the grizzly population itself has shown significant expansion, particularly in light of several drought years in which bears dramatically expand their home ranges in search of food. Natural disturbances such as large scale wildfires and years with lower white bark pine seed production may also contribute to expansions in distribution.

"Wilderness-Based Ecosystem Protection in the Northern Rocky Mountains of the United States," published in the USDA Forest Service proceedings of The Wilderness Science conference, concludes that wilderness habitat is a source habitat for remaining grizzly bear populations. This paper contains a spatial analysis of grizzly bear mortalities in the greater Yellowstone and Northern Continental Divide recovery ecosystems, using GIS. This paper reports that approximately 64% of all recorded mortalities in both areas occurred within 2 km of roads and 4 km of major developed areas. It also found that the spatial distribution of mortalities shifted from wilderness to non-wilderness habitat following the cessation of legal hunting seasons.

"Spatial Needs of Grizzly Bears in the U.S. Northern Rockies", presented this past summer as a spoken paper at The Society for Conservation Biology 2000 Meeting, estimates the spatial requirements for a viable population of 2,000-2,500 grizzly bears in the Northern Rockies falls within the range of 147,883-184,919 square kilometers (about 57,000-71,000 square miles) of habitat area. These calculations were based upon an analysis of estimated viable population size, mean density, area specific home range sizes, current and historic distribution areas, habitat security, and habitat productivity.

This report also analyzes U.S. Fish & Wildlife Service recovery goals for the grizzly bear, in comparison with data from the literature. For example, the total size of the recovery areas in the Northern Rockies is 71,082 km2 including the proposed Bitterroot recovery area, and 56,043 km2 without it, or just 48.1% and 37.9% respectively, of the lower end estimate for total spatial needs.

"The bottom line is, current recovery zones can't supply enough habitat area to add up to viable numbers for the population," Bader said.

Meeting these challenges will require bold action. For example, grizzly bear habitat in the northern Rockies is not contiguous. Rather it occurs as a series of spatially disjunct, semi-isolated blocks, none of which could support a population of 2,000-2,500, needed for long term viability. Thus, they must either be connected with a system of habitat linkage areas, bears be mechanically translocated from one area to another, or the blocks be managed as non-viable isolates. Spatial Needs of Grizzly Bears proposes a 190, 777 km2 (about 73,000 square miles) habitat system to solve this dilemma.

Spatial Needs of Grizzly Bears contains an extensive array of data derived from the literature on grizzly bear research from throughout the U.S. and Canada. This report contains 10 tables and 4 figures, including a full-color center spread map of the proposed habitat network. It also includes an analysis and ranking of potential linkage corridor habitats.

These papers make use of new GIS technology to conduct spatial analysis of data and to produce high quality maps for easy viewing as well as data sharing of digital information with other researchers.

Copies of these publications are available from Alliance for the Wild Rockies. Send requests by e-mail; phone: (406)721-5420; or regular mail: P.O. Box 8731, Missoula, MT 59807. A $2 donation for postage and materials is requested, but not required.