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Grand Teton National Park Report

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From 1987 through 1989 we undertook a study in Grand Teton National Park and on the upper Green River, Sublette County, Wyoming, to measure growth rates of cohorts of montane voles, (Microtus montanus) born in May, June, July, and August. We documented dramatic differences in growth rate among cohorts, in a given year and between years (Negus, Berger and Pinter, 1992). We hypothesized that these are flexible responses to several environmental cues. Is this, however, a phenotypic response to an array of environmental cues, or is it actually a reflection of differential utilization of plant species that may exhibit different nutritional levels? This question cannot be answered at the present since virtually nothing is known about dietary preferences of Microtus montanus. However, seasonal variation in food selection has been documented in several other species on voles (Rothestein and Tamarin, 1977, Cole and Batzli, 1979, Goldberg et al. 1980) with considerable implications for winter survival and population dynamics. In Microtus montanus a similar link may exist between growth, maturation, longevity, and population dynamics on the one hand and dietary composition on the other (e.g., Pinter and Negus 1965, Berger et al. 1981, Pinter 1988, Berger et al. 1992, Negus, Berger and Pinter 1992). Consequently, we undertook a study to investigate in detail the utilization of plant resources by the montane vole, Microtus montanus. The objectives of this project are twofold: (i) to identify the plant species that constitute the diet in natural populations of M. montanus and (2) to determine seasonal food preferences in relation to the availability of plant species and to the age, sex and cohorts of the montane vole.