Black bear population ecology Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5x21tj55d

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  • Despite relatively mild weather, black bears (Ursus americanus) in southwestern Washington entered dens and remained for an average of 126 days. Bears entered their dens during a 5-week period which began on 21 October. A significant difference (P < 0.05) was found among the average dates of den entrance of adult females, yearlings, and adult males. Adult females were the first bears to enter their dens; yearlings entered next, and adult males were the last to enter their dens. The stimulus to enter a den probably was provided by the cumulative effect of weather. The actual period of winter dormancy was preceded and followed by periods of decreased activity. Inactivity during the predenning and postdenning periods was correlated with daily weather, principally maximum daily temperature and precipitation. Dens of 11 transmitter-equipped black bears were investigated. Preferred den sites were natural cavities under stumps or snags which could be used with little preparation. Adult bears denned in areas cut before 1955; yearlings denned generally in areas cut after 1966. Adult females collected greater amounts of vegetative material for nests than did yearlings. Movement and activity of 16 black bears of a population of 23 bears were monitored by radio telemetry and visual observation between March 1973 and October 1975. Average home-range sizes of adult males (505 ha) and females (235 ha) were markedly smaller than home-range estimates for other parts of the United States. Richness of habitat on the island presumably allowed these small home ranges. Males varied more than females in seasonal use of their home ranges. Home ranges overlapped within and among sex and age groupings. Bears appeared temporally separated, with the use of areas where home ranges overlapped apportioned on the basis of a dominance hierarchy. Bears used certain vegetation types on the island disproportionately to the availability of these types, apparently selecting for areas logged since 1963 and against areas not logged since 1935. Results of a line of 28 scent stations run during four seasons for periods of 4 nights each suggested that scent stations are a potential means of indexing black bear numbers. The greatest relative index value (238) occurred during late May. Teeth and reproductive tracts were collected from bears killed in Oregon from 1971 to 1974. Analysis of female reproductive tracts indicated that females did not breed before they were 3-year -olds and that 23.4 percent did not breed first as 3-year-olds. Reproductive rates were estimated to be 0.87, 0.234 and 1.07 for 3-year-old, 4-year-old. and 5-year-old and older females respectively. Survival, rates estimated from a sample of 248 females employed in a timespecific life table, were 0.790, 0.859 and 0.811 for the same agegroupings. Average, annual survival rate for the sample of females was 0. 818; average, annual survival rate for females and males combined was 0.798. Neither the life equation nor the structural population model indicated that the sample had come from a population that was increasing or decreasing.
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