Arizona, New Mexico, Colorado & Utah
The technical papers and synoptic report featured on this page provide an overview of the history, current status, and future prospects of grizzly bears in Arizona, New Mexico, Colorado, and Utah. These states once had thriving grizzly bear populations, with individual bears surviving as last as the 1930s in Arizona and New Mexico. The last known grizzly bear in the Southwest was killed in 1979, in the San Juan Mountains of Colorado. Collectively, the analyses presented here describe ample opportunity for restoring grizzly bears to the Southwest, including robust populations in the Mogollon Highlands of Arizona and western New Mexico and the San Juan and Sangre de Cristo Mountains of Colorado and northern New Mexico.
You can download three technical papers and one report published by the Grizzly Bear Recovery Project on this page. The technical papers provide more detailed information on methods used to assess potential for recovery of grizzly bears in the Southwest: 1. a summary of contemporary grizzly bear densities and relations to habitat conditions; 2. a method for estimating potential densities as a function of habitat features; 3. a detailed geospatial analysis of recovery prospects. The report explores the deep history of grizzly bears and grizzly bear-human relations in the Southwest, a comprehensive appraisal of current potential for recovery, and an assessment of future prospects in the face of climate change and human population growth.
Grizzly Bear Recovery Project Technical Report GBRP-TR-2021-3
by David Mattson & Troy Merrill
We appraised the suitability of Arizona, New Mexico, southern Utah, and southern Colorado for restoration of grizzly bears Ursus arctos horribilis by extending and integrating existing models of habitat capability and remoteness from humans, calibrated to historical grizzly bear locations in our Southwest study area. We applied previously published standards or new standards based on established concepts to identify areas productive enough and remote enough from humans to sustain grizzly bears locally, as well as habitat complexes that were capable of supporting robust grizzly bear populations because of large size and high quality. We identified three promising complexes of suitable habitat ranging in size from 8,000 to >15,000 km2 : the Mogollon, San Juan, and Sangre de Cristo Complexes, of which the last two potentially functioned as one conservation area. These complexes of suitable habitat were, in turn, the basis for delineating three candidate Recovery Areas with estimated average carrying capacities of 620, 425, and 281 grizzly bears, respectively. We also assessed these candidate Recovery Areas for overlap with areas offering additional protections (e.g., Wilderness Areas and National Parks) as well as additional prospects of human-grizzly bear conflict (e.g., private property and public land sheep grazing allotments).
Grizzly Bear Recovery Project Technical Report GBRP-TR-2021-2
by David Mattson & Troy Merrill
We investigated relations between estimated grizzly bear Ursus arctos horribilis densities in 12 Rocky Mountain study areas and several potentially predictive or explanatory variables that included tassled cap transformed Thematic Mapper (TM) satellite imagery, the extent of whitebark pine Pinus albicaulis range, diet energy concentration, remoteness from humans, and study area size. Our objective was to develop models for predicting potential grizzly bear population sizes in areas currently unoccupied by bears, or supporting small and vulnerable populations. To test our models, we examined goodness of fit of predicted and observed densities in 5 additional study areas and determined whether predicted densities were spatially correlated with observations of grizzly bears in 2 regions. We also determined whether key predictive metrics correlated positively with a direct measure of habitat productivity in the Yellowstone region. Our best model included a single variable (Wetness from tasseled cap transformed TM imagery). This model optimized parsimony and fit and produced density predictions that correlated well with distributions of grizzly bear observations and fit observed densities in the 5 independent test areas. TM Wetness was also positively correlated with habitat productivity in the Yellowstone region. Based on this model, and without considering limiting human effects, we predicted that former 1850s range in Arizona and New Mexico could support 1905 bears (0–5059 prediction interval), that currently unoccupied but potential habitat in central Idaho could support 615 bears (443–757), and that habitat currently occupied by a very small (<40) and vulnerable population in northwestern Montana could support 362 bears (286–428).
Grizzly Bear Recovery Project Technical Report GBRP-TR-2021-1
by David Mattson
In this paper I provide an estimate of pre-European grizzly bear (Ursus arctos) population sizes and distributions for the contiguous United States along with a rationale for this estimate based on relations between contemporary grizzly bear densities and coarse-grain environmental features. I also present a comprehensive database of density estimates made for grizzly bear populations throughout western North America that updates an earlier version presented by Mowat et al. (2013). Contemporary grizzly bear densities in North America are positively associated with average annual precipitation and temperature; evapotranspiration; terrain ruggedness; and areas dominated by herbs and shrubs. Densities are negatively associated with consumption of meat from terrestrial sources and densities of livestock. A weaker negative relation with human densities is also evident. At the time of first contact with Europeans, I estimate that there were roughly 47,300 (SD = 15,300) grizzlies in what was to become the contiguous United States, distributed over an area of approximately 2,864,000 km2 .
Grizzly Bear Recovery Project Report GBRP-TR-2022-1
by David Mattson
For perhaps 30,000 years grizzly bears ranged throughout the mountains and riparian areas of what would eventually become the southwestern United States. But in a remarkably short 50-year period between 1860 and 1910 Anglo-Americans killed roughly 90% of the grizzly bears in 90% of the places they once lived. Most of the remaining grizzlies had been killed by the 1930s. This report provides a detailed account of natural history, relations with humans, and current and future prospects for grizzly bears of the Southwest, emphasizing the millennia prior to ascendence of Anglo-Americans.
The report’s narrative is essentially chronological, starting with deep history spanning the late Pleistocene up through arrival of European colonists (Section 3.1); the period of Spanish and Mexican dominance (Section 3.2); and then the period of terminal grizzly bear extirpations that began with the political and military dominance of Anglo-Americans (Section 3.3). Section 4 examines current environmental conditions and related prospects for restoring grizzly bears to the Southwest. Section 5 completes the chronological arc by forecasting some of what the future might hold, with implications for both grizzly bears and humans.
The background provided in Section 2 offers a synopsis of grizzly bear natural history as well as a summary of foods and habitats that were likely important to grizzlies. Throughout the Holocene there was a remarkable concentration of diverse high-quality bear foods in highlands of the Southwest, notably in an arc from the San Francisco Peaks of Arizona southeast along the Coconino Plateau and Mogollon Rim to a terminus in the White, Mogollon, and Black Range Mountains in New Mexico. Additional high-quality habitat existed in the Sacramento, San Juan, Jemez, and Sangre de Cristo Mountains of New Mexico and adjacent Colorado.
Grizzlies in the Southwest survived remarkable extremes of climate and habitats for perhaps as long as 100,000 years. They also survived substantial variation in human-propagated impacts that culminated in the Crisis of 875-1425 C.E.—a period typified by episodic drought and the highest human population densities prior to recent times. In contrast to relatively benevolent attitudes among indigenous populations, there is little doubt that the terminal toll taken on grizzly bears by Anglo-Americans after 1850 C.E was driven largely by a uniquely lethal combination of intolerance and ecological dynamics entrained by the eradication or diminishment of native foods and the substitution of human foods, notably livestock, that catalyzed conflict.
More positively, the analysis presented here of current habitat productivity, fragmentation, and remoteness—as well as regulations, laws, and human attitudes—reveals ample potential for restoration of grizzlies to the Southwest, including three candidate Restoration Area Complexes: the Mogollon, San Juan, and Sangre de Cristo, capable of supporting around 620, 425, and 280 grizzlies each. Major foreseeable challenges for those wishing to restore grizzly bears to these areas include sanitation of human facilities, management of livestock depredation, education of big game hunters, coordination of management, and fostering of accommodation among rural residents. Climate change promises to compound all of these challenges, although offset to an uncertain extent by prospective increases in human tolerance.
But the evolutionary history of grizzly bears also provides grounds for optimism about prospective restoration. Grizzly bears have survived enormous environmental variation spanning hundreds of thousands of years, including many millennia in the Southwest. Grizzlies survived not only the inhospitable deeps of the Ice Ages in Asia and Beringia, but also the heat and drought of the Altithermal on this continent. It was only highly-lethal Anglo-Americans that drove them to extinction in the Southwest, which is why human attitudes—more than anything else—will likely determine prospects for restoring grizzly bears.