Troy Merrill | Geology Reports

USGS2002

Extirpations of grizzly bears in the contiguous United States of America, 1850-2000

We investigated factors associated with the distribution of grizzly bears ( Ursus arctos horribilis ) in 1850 and their extirpation during 1850–1920 and 1920–1970 in the contiguous United States. We used autologistic regression to describe relations between grizzly bear range in 1850, 1920, and 1970 and potential explanatory factors specified for a comprehensive grid of cells, each 900 km 2 in size. We also related persistence, 1920–1970, to range size and shape. Grizzly bear range in 1850 was positively related to occurrence in mountainous ecoregions and the ranges of oaks ( Quercus spp.), piñon pines ( Pinus edulis and P. monophylla ), whitebark pine ( P. albicaulis ), and bison ( Bos bison ) and negatively related to occurrence in prairie and hot desert ecoregions. Relations with salmon ( Oncorynchus spp.) range and human factors were complex. Persistence of grizzly bear range, 1850–1970, was positively related to occurrence in the Rocky Mountains, whitebark pine range, and local size of grizzly bear range at the beginning of each period, and negatively related to number of humans and the ranges of bison, salmon, and piñon pines. We speculate that foods affected persistence primarily by influencing the frequency of contact between humans and bears. With respect to current conservation, grizzly bears survived from 1920 to 1970 most often where ranges at the beginning of this period were either larger than 20,000 km 2 or larger than 7,000 km 2 but with a ratio of perimeter to area of <2. Without reductions in human lethality after 1970, there would have been no chance that core grizzly bear range would be as extensive as it is now. Although grizzly bear range in the Yellowstone region is currently the most robust of any to potential future increases in human lethality, bears in this region are threatened by the loss of whitebark pine.

Arizona, California, Colorado, Idaho, Kansas, Mont↗

USGS1999

Defining landscapes suitable for restoration of grizzly bears Ursus arctos in Idaho

Informed management of large carnivores depends on the timely and useful presentation of relevant information. We describe an approach to evaluating carnivore habitat that uses pre-existing qualitative and quantitative information on humans and carnivores to generate coarse-scale maps of habitat suitability, habitat productivity, potential reserves, and areas of potential conflict. We use information pertinent to the contemplated reintroduction of grizzly bears Ursus arctos horribilis into central Idaho to demonstrate our approach. The approach uses measures of human numbers, their estimated distribution, road and trail access, and abundance and quality of bear foods to create standardized indices that are analogues of death and birth rates, respectively; the first subtracted from the second indicates habitat suitability ( HS ). We calibrate HS to sightings of grizzly bears in two ecosystems in northern Idaho and develop an empirical model from these same sightings based on piece-wise treatment of the variables contained in HS . Depending on whether the empirical model or HS is used, we estimate that there is 14 800 km 2 of suitable habitat in two blocks or 37 100 km 2 in one block in central Idaho, respectively. Both approaches show suitable habitat in the current Evaluation Area and in an area of southeastern Idaho centered on the Palisades Reservoir. Areas of highly productive habitat are concentrated in northern and western Idaho and in the Palisades area. Future conflicts between humans and bears are most likely to occur on the western and northern margins of suitable habitat in central Idaho, rather than to the east, where opposition to reintroduction of grizzly bears is currently strongest.

Idaho↗