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Abstract

During the summer of 1960, an attempt was made to evaluate reproduction in populations of Microtus montanus in relation to the growing season of the primary food plants. Extensive sampling of the populations was undertaken during July and August. A live-trapping unit was established in which all animals were marked and released. Females captured in this unit were X-rayed in the laboratory to obtain live embryo counts before release back into the unit. In this way we hoped to follow reproductive regimes in individuals through the season. Eventual failure of the X-ray apparatus precluded successful completion of this program. Samples of bluegrass (Poa pratensis) were collected at intervals throughout the study for chemical analysis in the laboratory during the fall and winter months. Known-age litters of young Microtus montanus were born and reared in the laboratory to obtain growth rate curves. Growth rates were determined up to 6 weeks of age. From these data approximate age determination was possible for most young animals taken during the summer. Project Number 110.

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