FORAGING STRATEGY AND PREDATION RISK AS FACTORS INFLUENCING EMERGENCETIME IN ECHOLOCATING BATS

We hypothesized that interspecific differences in evening emergence ti me among echolocating bats are subject to natural selection through ef fects of variation in food availability and predation risk, both of wh ich are related to flight technique and foraging strategy. We predicte d that bats that feed on small aerial insects emerge relatively early to get access to the peak in flight activity of small dipterans at dus k. By emerging well before dark, however, they expose themselves to in creased risks of predation and/or harassment from raptorial or insecti vorous birds which may still be active. Bats that can feed independent ly of the dusk peak of dipterans, i.e. those that are adapted to feed on moths, on flightless or diurnal prey or on plants, would be expecte d to emerge later, thus minimizing the predation risk. We tested these predictions by analysis of two data bases: one including European bat s only and another including a worldwide sample. The predictions were largely supported. The evening emergence time appears to be a function of dietary specializations and foraging strategy, and is probably als o affected by the ability to avoid predation.