FLIGHT PERFORMANCE, FORAGING TACTICS AND ECHOLOCATION IN THE TRAWLING INSECTIVOROUS BAT MYOTIS-ADVERSUS (CHIROPTERA, VESPERTILIONIDAE)

The bat Myotis adversus hunts for prey by aerial hawking and by taking prey from the water surface with its feet (trawling). The flight performance and echolocation of this species were studied in Queensland, Australia, and comparisons were made with Myotis daubentoni, a bat filling a similar ecological niche in the Palaearctic Region. The bats foraged in very similar ways, using the same foraging tactics and feeding in similar habitats, yet they were not geometrically similar in shape. The slightly larger Myotis adversus had relatively larger wings than M. daubentoni, conferring a slightly lower wing-loading. Nevertheless, M. adversus flew faster than M. daubentoni during the searching phase of foraging. Myotis daubentoni turned in tighter circles than M. adversus. Both species used short frequency-modulated (FM) echolocation calls of a characteristic sigmoidal structure, and nulls typically observed in the calls were an observational artefact. Myotis adversus also adopted an unusual 'long' FM call while foraging. The relations between echolocation frequencies and body size were explored in male M. adversus. Specialized morphological and acoustic adaptations for prey capture by trawling in insectivorous bats are discussed.