Sensory aspects of foraging behaviour in a foliage-gleaning bat, Plecotus auritus
The brown long-eared bat Plecotus auritus (Chiroptera: Vespertilionidae) feeds predominantly on large moths and beetles, some of which are obtained by gleaning from leaves and other surfaces such as walls. As little is known about the importance of gleaning in the foraging behaviour of this species, or the sensory mechanisms used to locate prey, the aim of the present study was to examine sensory aspects of gleaning. Observations of foraging behaviour of captive bats feeding on moths showed that about half the prey was obtained by gleaning, the remainder was captured in flight. Echolocation calls were rarely emitted by gleaning bats, and attempts to capture prey were more successful when echolocation was not used. Bats were equally successful at capturing prey in the air or from substrates. Aerial pursuit of moths involved echolocation, and typical calls were short in duration (less than 2ms) and contained frequencies between 20-120 kHz. In two-choice discrimination trials, Plecotus auritus was able to discriminate between fluttering and immobile moths by listening to the sounds made by the prey. Spectral analysis revealed that the moths' fluttering sounds were below 20 kHz in frequency. There was some evidence of interspecific variation in the spectral qualities of sounds made by fluttering moths although it was not possible to determine if this variation was used by the bats as a basis for prey selection. Neurophysiological examination of the auditory system revealed adaptations associated with passive listening. These included low thresholds of sensitivity to sounds in the range 8-20 kHz, which encompasses the frequencies found in the sounds made by moving prey.