Movement as a specific stimulus for prey catching behaviour in rhinolophid and hipposiderid bats

Abstract

1. The echolocating ‘long CF/FM-bat’Rhinolophus rouxi and the ‘short CF/FM-bats’Hipposideros bicolor andHipposideros speoris were tested for catching responses to moving and non-moving targets. 2. Under our experimental conditions (freshly caught caged bats in a natural environment)Rhinolophus rouxi andHipposideros speoris only responded to insects of any sort that were beating their wings. The bats showed no reactions whatsoever to nonmoving insects or those walking on the floor or the sides of the cage. 3. Hipposideros bicolor responded in the same way as the above species to wingbeating insects but in addition also attacked walking insects. In 27 presentations 15 walking insects were caught (Fig. 2). 4. Rhinolophus rouxi, Hipposideros speoris andHipposideros bicolor also detected, approached and seized tethered cockroaches hanging from the ceiling when these were vibrating up and down (Fig. 3). This indicates that any oscillating movement and not specific aspects of wing beating were the key releasers for catching behaviour in all three species. However, a wing beating insect is strongly preferred over a vibrating one in all three species (Fig. 4). 5. Rhinolophus rouxi, Hipposideros speoris andHipposideros bicolor attacked and seized a dead bait when it was associated with a wing beating device (Fig. 1). All three species responded effectively to beat frequencies as low as 10 beats/s (peak-to-peak amplitude of the wing excursion 20 mm). For lower frequencies the response rates rapidly deteriorated (Fig. 5). 6. Horseshoe bats no longer responded to wing beats of 5 beats/s when the wing beat amplitude was 2 to 1 mm or to wing beats of 2 to 1 beats/s when the amplitude was 3 mm or lower (Fig. 6). This suggests that the speed of the wing is a critical parameter. From these data we infer that the threshold for the catching responses is at a wing speed of about 2 to 1 cm/s. 7. In horseshoe bats (experimental tests) and the two hipposiderid species (behavioural observations) one single wing beat was enough to elicit a catching response (Fig. 8). 8. It is concluded that ‘long’ and ‘short’ CF/ FM-bats feature a similar responsiveness to fluttering targets. The sensitivity to oscillating movements is considered as an effective detection mechanism for any sort of potential prey.