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UBC Theses and Dissertations

Ecology, population dynamics, and management of the black bear in the spruce-fir forest of Northwestern Montana Jonkel, Charles J.

Abstract

This research was designed to study the ecology and population dynamics of black bears in the spruce and fir forest of northwestern Montana, to test the hypothesis that extrinsic factors caused fluctuations in population numbers, and to develop management principles for bears. The rough topography and moderate to heavy precipitation on the Big Creek study area have created varied ecological conditions which in many ways are excellent for black bears. Seral and climax stands of the Picea-Abies/ Pachistima myrsinites association are used most extensively by bears, but other vegetative types are important seasonally. The home ranges of adult bears on the area are small and they remain the same size from year to year. As resident males mature, however, their ranges increase in area. Bears do congregate, but only where there is an overlap in their home ranges. Even then they do not form compact groups, but keep at least 50 yards (48 metres) between individuals. Many adult females (bears approximately 4-1/2 years or older) do not have young, apparently because of the failure of females to ovulate, prenatal mortality, and early mortality. Tentative conclusions suggest that seasonal restrictions in nutrition delay the physical maturity and thereby the sexual maturity of some bears. These restrictions are caused by the climate of Big Creek and are detrimental even to adult females on certain years. Inadequate nutrition is also suggested by the observation that some yearlings inhibit estrus for two years by suckling up to 16 months of age. The nutrition of adult males and of many adult females generally is excellent, however. Litter sizes on Big Creek and throughout the West are smaller than in eastern North America, but apparently the cause is genetical rather than nutritional. The survival of cubs is high (95 per cent) from 1/2 to 1-1/2 years of age while they are with their mothers, but all sub-adults are physically weak in late spring and natural loss is considerable among sub-adults 1-1/2 to 3-1/2 years old. They appear especially vulnerable to changes in climate, parasitism, predation, food quantity and quality, and the behaviour of adult bears. Many sub-adult males disperse from the area. Annual changes in the density of bears on Big Creek are caused in part by man, by dispersal of sub-adults, and through changes in the reproductive success of adults and the natural mortality of sub-adults. The numbers of adults on the area remain relatively constant from year to year. Even though food is unlimited during some seasons, a form of territoriality within "social groups" spaces the bears on Big Creek and ultimately exerts a definite control over density. The density is relatively high on Big Creek and probably results in more social interaction and territoriality than in bears elsewhere. Longer care of young, smaller litter sizes, and increased social organization all seem evident as reactions to the Big Creek environment. Extrinsic and intrinsic forces unite, therefore, in population regulation, and the net result is the creation of an excellent habitat for adult black bears, but an harsh, environment for sub-adults after they have left their mothers.

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