Population Characteristics of Black Bears on an Island in Washington

Abstract

Twenty-three black bears (Ursus americanus) were captured on an island in southwestern Washington. Age structure of the population indicated that it was young and growing, and that breeding was relatively synchronized. Density of bears over a year of age (1 bear per 89-67 ha) on the island was high in comparison to estimates of density elsewhere in North America. J. WILDL. MANAGE. 41(3):408-472 Black bear densities vary over their range in North America. Locally, densities may be influenced by habitat quality (Jonkel and Cowan 1971, Lindzey and Meslow 1977) and hunting (McIlroy 1972:837, Wakefield 1972:51). Behavior patterns may be the proximal determinant of densities; the role of behavior often may not be apparent, however, because of low population numbers. Behavior that determines dispersion patterns is presumably not independent of the influence of habitat, but flexible (behavioral scaling, Wilson 1975:19) in response to quality of particular habitats. Jonkel and Cowan (1971:35) observed female cubs that established permanent residency in their mother's home range; such behavior would presumably be disadvantageous to the adult female if resources were scarce. The extension of family relationships as observed by Jonkel and Cowan (1971:38) may influence not only densities but sex and age composition of local populations as well. These population attributes through behavioral scaling thus may reflect habitat quality. Hunting may interfere with the establishment of associations that would provide these patterns in a population. This paper reports on the demographic characteristics of a lightly-hunted population of 23 black bears on an island in southwestern Washington. Dispersion of members of this population suggested tolerance among related individuals (Lindzey and Meslow 1977). J. M. Welch, refuge manager, Willapa National Wildlife Refuge, H. Hardesty, and R. Van Wormer provided logistic support during the study. S. D. Lindzey, R. Walker, R. Libby, A. K. Miles, and W. Welch assisted with field work. The late H. M. Wight provided encouragement and advice. H. C. Black, J. A. Crawford, D. S. deCalesta, and C. J. Jonkel gave valuable criticisms of the manuscript. The Weyerhaeuser Company and Washington Department of Game granted permits necessary to conduct the study.