Reproductive Characteristics of Red-Backed Mouse during Years of Differing Population Densities

Abstract

Small mammal populations were sampled over a nine-year period in the Central Adirondack Mountains. Populations varied considerably from year to year, with highs in 1953 and 1959. Clethrionomys was the principal species sampled, and to a large degree accounted for the 1953 and 1959 highs. Evidence of similar population variations is available for Blarina , with a much lower amplitude of fluctuation observed. Low Bhrina populations were followed by rapid increases in Clethrionomys . There is some slight evidence that Peromyscus populations reach a peak every three years. At this time it is too early to state whether or not any of the observed variations are cyclic. It was found that Clethrionomys populations reproduced more successfully during periods of low populations than during periods of high populations. Litter size was inversely proportional to population density. In addition, a higher percentage of adult females engaged in reproduction during the periods of low populations.