Biology of the Arctic Shrew, Sorex arcticus

A population of arctic shrews, Sorex arcticus, living in a grass-sedge marsh in southern Wisconsin, was studied for three years. Two North American Census of Small Mammal trap lines operated for 28 months revealed six other species of small mammals living in the same area. Results showed neither positive nor negative association of the different species at trapping stations. The population fluctuations of the arctic shrew appeared to be independent of those of the other small mammals. Age determination was done by measurement of tooth wear. Young arctic shrews appeared first in July and disappeared after July of the following year. Males came into breeding condition in February. Females became pregnant by mid-May at the latest. Young animals did not commonly breed in their first season. The average embryo count of four females was six. Adult animals were heavier and longer than young but had similar skull measurements. The dull coat pattern of the young was replaced by the tricolor in the fall and this tricolor coat pattern was retained by the adults in the following summer. The rate of shrew capture in live traps was slightly lower in early morning than at other times of day and night. The behavior of the arctic shrew in captivity is described with notes on feeding habits and interactions with meadow voles.