The Habitat Preference of Microtus pennsylvanicus, and Its Relevance to the Distribution of This Species on Islands

Abstract

Microtus pennsylvanicus normally occurs in grassland habitat but is occasionally found in woodland, most frequently on islands. To help understand why the woodland is sometimes occupied, experiments were conducted in outdoor enclosures to study habitat preference and movement from grassland to woodland. A strong preference for grassland was demonstrated. Adults with previous experience in grassland and young voles without such experience, but held in the woodland for 2 weeks, were released in the woodland. All voles entered the grassland soon after release and remained there. In another enclosure a population was allowed to build up in the grassland. Movement into woodland occurred only at high density. It is believed that intraspecific interaction, associated with high density, induced the movement. It is suggested that this and the absence of competitors and predators are the chief factors responsible for the occurrence of M. pennsylvanicus (and other mammal species) in unusual habitat on islands.