Northern Prairie Wildlife Research Center
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).
Table of Contents
Tables and Figures
- Table 1 -- Estimated numbers of black
bears using a 218-km² area near Cold Lake, Alberta, 1968-77.
- Table 2 -- Kaplan-Meier estimates of
mortality rates from deaths due to all agents and natural agents only for
radiocollared black bears.
- Table 3 -- Numbers of individual black
bears captured annually at Cold Lake, Alberta, May-Sep, 1968-77.
- Figure 1 -- The Cold Lake bear study area
(CLSA).
- Figure 2 -- Trends in estimated numbers
of bears using the CLSA during 1968-77.
- Figure 3 -- Demographic concepts are ambiguous
when small study populations are arbitrarily delimited.
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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