Echolocation behaviour of Megaderma lyra during typical orientation situations and while hunting aerial prey: a field study.

Bats modify the structure and emission pattern of their calls to cope with the functional constraints of a given echolocation situation. As a consequence, the flexibility in sonar call use affects the potential niche use of a species. The present paper addresses call use in Megaderma lyra, a species with a short, broadband multiharmonic basic call, in typical orientation situations, when emerging from and re-entering a day roost, in cruising flight and when passing through vegetation, and during the pursuit of tethered, flying insects. While call duration and emission rate were adapted to the four orientation situations, call spectral composition was similar in these situations, except that bats emitted calls containing more harmonics when re-entering the roost. These moderate call modifications may be accounted for by the observation that M. lyra stayed close to landscape elements even in open habitats. Although M. lyra is a typical gleaner, all tested bats approached flying insects, guided by sonar calls of significantly decreasing duration and pulse interval, and of increasing sweep rate. Before capture, peak frequency was lowered from call to call. The spontaneous approaches towards flying insects with systematic changes in call pattern suggest regular aerial hunting in this species.