Young flying squirrels (Pteromys volans) dispersing in fragmented forests

Dispersal is a key determinant of the population dynamics of species. Thus, a better understanding of how dispersal is affected by the landscape structure and how animals make decisions about moving across different landscapes is needed. We studied the dispersal of 60 radio-collared juvenile Siberian flying squirrels (Pteromys volans) in southern Finland. The effect of landscape structure on selected dispersal direction, dispersal distance, and straightness of dispersal path was studied. Flying squirrels were capable of dispersing over long distances in fragmented forest landscapes. The patches used as temporary roosting sites during dispersal were of a lower quality than were those used as finally occupied patches. The patches used were larger than were patches on average in the study areas. There was a very clear directional bias in the dispersal path (i.e., it was nearly a straight line), which remained over a large scale, but wide-open areas obstructed the straightness of the path. As the distances between crossed patches increased, short-distance dispersers were found further away from their natal home range. However, there were no differences in the landscape that could explain the differences between individuals in decisions to remain philopatric or to become short- or long-distance dispersers. In addition, whereas short-distance dispersers dispersed in random directions, long-distance dispersers started to disperse in directions dominated by preferred habitat. Thus, there were behavioral differences between dispersers. Our results supported the hypotheses stating that individuals decide to disperse long or short distances before the onset of dispersal.