Active acoustic gleaning from the water surface by the Indian false vampire bat, Megaderma lyra

Abstract

1. The method employed by the Indian false vampire bat Megaderma lyra (body mass about 40 g) to detect and capture prey from the surface of an artificial pond in an outdoor enclosure was studied. Frogs (Rana tigerina) (body mass about 10 g) were used as prey. The bats exhibited searching flights at the surface of the water for a few minutes in darkness, detected a stationary frog with its head jutting out of the water, and with a dart captured the frog in the mouth after hovering over it for about 2 s. The detected frogs did not show any movement when the bats hovered over them. 2. When a freshly killed frog alone was available and pinned with its head protruding out of the surface of the water, the bats captured it after making fewer numbers of attempts in a shorter period of time compared with the capture of live frogs. The number of attempts and time taken to capture a frog increased when the frog's eyeballs alone were exposed above the water surface, and the bats failed to detect frogs when their entire head was submerged just below the water. 3. Sound and video recordings showed that M. lyra continuously emitted faint ultrasounds while making searching flights at the pond. Apparently the bats made 'early' and 'late' detections, with higher repetition rates of sound emission in the case of the latter. A final buzz before capturing prey was not recorded and the change in the duration of emitted sounds during approach and after capturing the frog was marginal. The second harmonic at 43.6 kHz (SD 3.5 kHz) was more dominant and the duration was 1.0 ms (SD 0.2 ms). 4. It is clear that M. lyra uses echolocation to detect and capture prey from the water surface. A comparison is made with an earlier report on M. lyra catching prey from the ground by a passive acoustic location.