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The behaviour of Vancouver Island marmots, Marmota vancouverensis Heard, Douglas C.

Abstract

I studied the social behaviour of the Vancouver Island marmot, Marmota vancouverensis, during the summers of 1973 and 1974. Virtually nothing was known about the behaviour of this species at the outset of this study, Barash (1973b, 1974a) suggested that the social behaviour and social organization of marmot species was determined by the severity of the environment (the vegetative growing season) and its effect on the growth rate of marmots. He predicted that marmot species living in short growing season environments would be highly social but that social tolerance would decrease as the growing season increased. The objective of this study was to test this hypothesis by observing the social behaviour of Vancouver Island marmots and comparing this to the length of the vegetative growing season. M. vancouverensis is endemic to Vancouver Island, British Columbia. The original colonizers of this species probably crossed to Vancouver Island via land connections that existed during the Illinoian glacial period, approximately 100,000 years ago, and survived subsequent glacial maxima on nunataks and coastal refugia or both. Vancouver Island marmots have been isolated from mainland forms for a length of time (10,000 to 100,000 years) sufficient to show specific evolutionary adaptations to their Vancouver Island environment. Vancouver Island marmots live in small colonies in the subalpine parkland. Social groups consisted of one adult male, one adult female, and variable numbers of two-year-olds, yearlings, and infants. Social groups were highly integrated with a large amount of communication occurring among colony members. Alarm calls were given in response to potential predators and could be heard over the whole colony. Short whistles were given in response to aerial predators (e.g. eagles) and long whistles were given in response to terrestrial predators (e.g. black bears). Both calls are narrow bandwidth sounds, a characteristic that makes them difficult to locate. The most common social behaviour that occurred among colony members was a nose touching behaviour termed greeting. All age-sex classes of Vancouver Island marmots engaged in greetings as well as other social behaviour patterns in about the same proportions. The vegetative growing season experienced by Vancouver Island marmots was approximately the same as that of M. flaviventris but the social behaviour of Vancouver Island marmots most closely resembled M. olympus, a species living where the growing season is much shorter. On this basis I rejected Barash's hypothesis that the length of the vegetative growing season is sufficient to account for the variability that Barash observed among marmot species. I suggest that vegetative growing season not be used as an index of growth rate but that the time taken to reach adult size be measured directly. The degree of social tolerance is positively correlated with the length of time required to reach maturity.

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