RAPTORS AND BATS - THREATS AND OPPORTUNITIES

To quantify the opportunity that emerging bats present to raptors and the risks that hunting birds pose to these bats, predator-prey responses were documented by (1) counting emerging bats and recording their emergence patterns and (2) monitoring the presence of raptors and quantifying the incidence of raptor attacks on bats. Hobby falcons, Falco subbuteo, African goshawks, Accipiter tachiro, and Wahlberg's eagles, Aquila wahlbergi, succeeded in 51% of 59 attacks on bats. The attacks occurred in woodlands (two attacks in 10 samples), and as bats emerged from colonies in buildings (three in 39 samples) and bridges (54 in 32 samples). Wahlberg's eagles and hobby falcons attacked by stooping at flying bats while African goshawks pursued them in flight. The birds usually took each captured bat to a perch to consume it, achieving handling times (from capture to eating to resumption of hunting) of 30-300 s. The raptors could maximize their use of bats by rapid handling of captures and by hunting at sites where bats were most numerous. This combination of factors meant that bats could form a significant portion of the diet of opportunistic raptors. Flying and emerging bats responded to attacks or potential attacks. For colonies of less than 100 bats, there was no relationship between emergence time and colony size, while bats tended to emerge significantly earlier from colonies of greater than 100 individuals. In all colonies, increasing numbers of bats decreased the risk of raptor attack to any individual. In colonies of less than 100, individuals could decrease their risk of attack by switching roosts, and by adjusting the times and durations of their emergences. Bats emerged earlier from larger colonies despite the increased risk of attack by raptors. © 1993 The Association for the Study of Animal Behaviour.