Insect pursuit, prey capture and echolocation in pipestirelle bats (Microchiroptera)

Abstract

The foraging and echolocation behaviour of three European pipistrelles ( Pipistrellus pipistrellus, P. nithusii and P. kuhlii) was studied under natural conitions. The pipistrelles were photographed with two 35 mm cameras under stroboscopic illumination, and their echolocation signals were recorded simultaneously. This permits a three-dimensional reconstruction of the flight paths of bat and prey, and allows the details of echolocation behaviour to be studied in the context of natureal foraging behaviour. The general relationships between foraging and echolocation behaviour were consistent among the three species. Foraging behaviour consisted of four stages: search flight (before detection of prey), approach flight (pursuit after detection of prey), capture and retrieval of prey. These stages correlated with phases in echolocation behaviour: search, approach, and terminal phase followed by a pause. Detection of prey occurred at distances of 1·14−2·20 m. The search cone extending from the bat's mouth was up to 150° wide. The pipistrelles caught prey in mid-air, either with the tail membrane alone or by funnelling it with a wing onto the tail membrane. Except for some intra- and interspecific differences in sound duration, pulse interval, bandwidth and terminal frequency in search phase, the structure and pattern of the echolocation signals were similar in the three pipistrelles. In the approach and terminal phases, pulse duration and pulse interval decreased with the approach to the target, while bandwidth and sweeprate increased. While pursuing insects, the pipistrelles precisely avoided an overlap between outgoing signal and the echo returning from the prey. Furthermore, the bats stopped emitting signals several centimeters before they reached the insect.