Intersexual attraction in natal dispersing root voles Microtus oeconomus

By an enclosure experiment we tested whether natal dispersing root voles Mi crotus oeconomus (Pallas, 1776) were prevented from colonising already occu pied habitat patches or if they were attracted to habitat patches by potent ial mates. The treatment consisted of manipulating the presence of animals in immigration patches, either with the presence of a solitary sexually mat ure male or female, whereas empty patches were used as a control. Immigrati on patches were separated from a patch used for release of a matriline (mot her with her newly weaned litter) by a semipermeable fence allowing only in terpatch movements of young animals. We predicted that either a social fenc e would prevent immigration to treatment patches, or that potential mates w ould attract dispersing individuals. In particular we expected fewer disper sing males to colonise male occupied patches, and fewer dispersing females to colonise female occupied patches due to intrasexual competition, ie an i ntrasexual social fence. We found that a higher proportion of females settl ed in male treatment patches than in female patches, whereas male dispersal was unaffected by treatment. Thus, the observed female immigration pattern appeared to be an attraction to patches occupied by the opposite sex. We f ound no sign that immigration was prevented by a social fence.