A Demographic and Gentic Study of House Mice, Mus musulus, Colonizing Pasture Haystacks on a Cereal Farm

Abstract

Demographic and genetic parameters were used to compare mice colonizing new ryegrass haystacks and mice captured in nearby fields. Two of the haystacks were exclusion-fenced, and mice were caught in entry and exit traps. Some mice moved repeatedly into and out of the fenced haystacks. Of those that left, 54% of males and 61% of females re-entered. There were no differences in age structure, sex or mean weight of those colonizers that permanently left the fenced haystacks and those that left and re-entered. During the 19-month study the colonizers appeared to represent a random set of individuals from the surrounding population. Colonizers of the haystacks survived longer and bred much better than mice in the surrounding fields. Overall, the haystacks provided an important refuge for mice when breeding and survival in neighbouring cereal crops and crop margins were severely reduced.