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Grand Teton National Park Report

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Cyclic fluctations in the popu]ation density of rnicrotine rodents have been known since antiquity. However, factors responsible for this phenomenon are not known. The objectives of this long term study are essentially threefold: 1. characterize those environmental variables that might affect Microtus montanus in different seasons of the year; 2. record the growth, maturation and reproductive activity of the voles under natural conditions; and 3. determine the maturational, as well as, the seasonal pelage changes of these rodents. The data resulting from the execution of the above objectives would be correlated in an attempt to determine the causes undedying the multiannual fluctuations in the population density of these microtine rodents in Grand Teton National Park.