Social and Population Structure in the Brown Long-Eared Bat, Plecotus auritus

Abstract The brown long-eared bat (Plecotus auritus) is a Palaearctic species with low wing loading and low aspect ratio, which feeds primarily by gleaning. Like most temperate-zone bat species, P. auritus forms colonies during summer. However, this species is unusual in that adult males are present within these colonies. Using both ecological and genetic techniques, the pattern of social organization and population structure was determined for this species close to the northern border of its distribution. A ringing study conducted at 30 summer roost sites determined that P. auritus formed small, mixed-sex colonies, with natal recruitment and long-term association to the colony in both sexes. Little exchange among roosts was identified; just six movements were recorded from 1138 recaptures and no individual was caught for a second time at a new site. P. auritus was found to be highly selective of its summer roost site at this latitude, which may explain the high natal philopatry and colony stability identified. Mean colony relatedness was low. This is probably a result of low skew in male reproductive success and a high incidence of inter-colony mating; over 80% of colony offspring were fathered by males from other summer colonies. Such a pattern of mating suggests that neither inbreeding avoidance nor competition for mates is likely to force males to disperse from their natal colony. The strong spatial distribution of individuals in the summer population was not reflected in patterns of genetic structure. Low levels of genetic differentiation among colonies were identified, probably as a result of inter-colony mating. However, genetic isolation by distance was evident within the population, suggesting that mating among colonies is restricted to those located close by. It is proposed that, at high latitudes, social organization and population structure in P. auritus are strongly influenced