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Demographic Response of Black Bears at Cold Lake,
Alberta, to the Removal of Adult Males

Glen A. Sargeant and Robert L. Ruff


Abstract: Previous reports described an increase in population density following the removal of 23 adult and 3 subadult male black bears (Ursus americanus) from a 218-km² study area near Cold Lake, Alberta (the CLSA). This finding plays a central role in continuing debates over population regulation in bears, but has been criticized because density estimates were based on assumptions that were not met. Moreover, subsequent discussion has be predicated on conjecture that human exploitation had minimal influence on population dynamics. We used improved methods of mark-recapture and survival analysis with a combination of new and previously published data to resolve these issues. Jolly-Seber estimates suggest numbers of females using the CLSA were relatively stable from 1969 to 1971, then more than doubled when males were captured and euthanized during 1971-72. Numbers remained high until 1975, when they declined abruptly. Similarly, numbers of subadult males captured annually increased disproportionately in 1972 and remained high until 1976, when they also declined. Changes in numbers of subadult males captured indicated changes in local density because they were not caused by changes in capture or settling rates. These findings support previous descriptions of trends in bear density at Cold Lake. However, survival records of 56 bears radiomarked during 1974-77 revealed heavier exploitation than previously suspected. Annual mortality rates of radiomarked bears ranged from 14 to 51%, and humans caused at least 25 of 30 observed deaths. Consequently, an underlying assumption of previous interpretations—that the Cold Lake bear population was naturally regulated near carrying capacity—no longer seems reasonable. Our results suggest that adult males deterred bears in other sex-age groups from using the CLSA; however, we found no evidence that birth or death rates were affected. Thus, the observed increase in local density should not be construed as a density-dependent response. Abrupt changes in local density might not have occurred if males had been removed from a larger area encompassing the CLSA.

Key Words: Alberta, black bear, compensatory mortality, density dependence, limiting factors, mark-recapture, population dynamics, population regulation, Ursus americanus


This resource is based on the following source (Northern Prairie Publication 1156):
Sargeant, Glen A., and Robert L. Ruff.  2001.  Demographic response of black 
     bears at Cold Lake, Alberta, to the removal of adult males.  Ursus 
     12:59-68.

This resource should be cited as:

Sargeant, Glen A., and Robert L. Ruff.  2001.  Demographic response of black 
     bears at Cold Lake, Alberta, to the removal of adult males.  Ursus 
     12:59-68.  Jamestown, ND: Northern Prairie Wildlife Research Center Online.  
     http://www.npwrc.usgs.gov/resource/mammals/coldlake/index.htm
     (Version 21FEB2003).

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Glen A. Sargeant, U.S. Geological Survey, Northern Prairie Wildlife Research Center, 8711 37th Street Southeast, Jamestown, ND 58401, USA. Email: glen_sargeant@usgs.gov
Robert L. Ruff, Department of Wildlife Ecology, 226 Russell Labs, 1630 Linden Drive, University of Wisconsin, Madison, WI 53706, USA.
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