Foraging, colonial and maternal behaviour of bats in North-East Scotland
Nursery colonies were formed by Pipistrellus pipistrellus, Plecotus auritus and Myotis daubentoni in mid May, and young were born, reared and weaned in these colonies. The time of dusk emergence of P. pipistrellus from the roost was controlled by light intensity, and although its rate depended on colony size, bats frequently emerged in bursts. Nightly activity patterns of P. pipistrellus were affected by the reproductive state of bats, and showed peaks at dusk and before dawn during lactation but only a dusk peak at other times. Nightly insect abundance showed dusk and dawn peaks throughout the summer. P. pipistrellus fed opportunistically on the insects most abundant, mainly Nematocera and Trichoptera. Although they selected Ephemeroptera and Neuroptera whenever they were available, these insects formed a small proportion of their diet overall. No differences were found between the diets of male and female pipistrelles, nor between those of females in different reproductive states. P. pipistrellus hunted in riparian habitats up to 5.1 km distant from their roosts, and moved on a regular "trap-lining" route between feeding sites. They travelled between sites in groups, and foraged on beats which were seldom defended. The recorded rate of attempted feeding was proportional to insect density until a maximum rate was reached, and intraspecific aggression was evident only at low insect densities. Juvenile bats learned to fly, navigate and forage within a period of three weeks. Colonies of P. auritus and M. daubentoni sharing a roost partitioned their resources by leaving the roost to forage at different times and by hunting for different insects in different habitats. Gestation length in P. pipistrellus varied over two years when weather, conditions, and hence food supply, differed. The rate of fetal development appeared to depend on maternal body temperature, which was maintained at a high level throughout pregnancy if the food supply was adequate. Female P. pipistrellus, P. auritus and M. daubentoni suckled only their own infants, which they recognized mainly by acoustic and, to a lesser extent, olfactory cues.