EXPLOITATION OF INSECTS AROUND STREETLAMPS BY BATS IN SWEDEN

1. Nine species of insectivorous bats in southern Sweden were monitored with a bat detector to assess which species regularly forage around streetlamps and which do not. Only the fast-flying species that use long-range echolocation systems (Nyctalus noctula, Vespertilio murinus, Eptesicus nilssonii and occasionally Pipistrellus pipistrellus) did, whereas Myotis spp. and Plecotus auritus did not. 2. Bats foraging near street lamps were monitored with a bat detector from a car. Bat density along illuminated roads was 1-5 km-1. More than 90% of the bats detected were E. nilssonii. 3. In and around a small town, E. nilssonii was predominantly found in residential and rural parts, and avoided areas without trees. Vespertilio murinus, in contrast, was observed in all habitats. The difference was probably related to differences in the foraging behaviour of the two species. 4. The attractiveness to insects by streetlamps was determined photographically. The various lamp types attracted insects in relation to the amount of short wave-lengths emitted. Bats were attracted to the same lamp types as insects. 5. The gross energy intake of E. nilssonii foraging around streetlamps was more than twice as high (0.5 kJ min-1) as previously recorded in woodlands (0-2 kJ min-1) but slightly lower than over pastures where dung beetles occurred (0.6 kJ min-1). 6. The results have implications for the conservation of bats. Generally, the fast-flying species will probably be least likely to suffer from a general decline in insect abundance. Priorities should therefore be given to the needs of the slow-flying bat species.