Echolocation calls ofMyotis lucifugusandM. leibii(Vespertilionidae) Flying Inside a Room and Outside

The influence of bat echolocation call duration and timing on auditory encoding of predator distance in noctuoid moths

Animals co-occur with multiple predators, making sensory systems that can encode information about diverse predators advantageous. Moths in the families Noctuidae and Erebidae have ears with two auditory receptor cells (A1 and A2) used to detect the echolocation calls of predatory bats. Bat communities contain species that vary in echolocation call duration, and the dynamic range of A1 is limited by the duration of sound, suggesting that A1 provides less information about bats with shorter echolocation calls. To test this hypothesis, we obtained intensity-response functions for both receptor cells across many moth species for sound pulse durations representing the range of echolocation call durations produced by bat species in northeastern North America. We found that the threshold and dynamic range of both cells varied with sound pulse duration. The number of A1 action potentials per sound pulse increases linearly with increasing amplitude for long-duration pulses, saturating near the A2 threshold. For short sound pulses, however, A1 saturates with only a few action potentials per pulse at amplitudes far lower than the A2 threshold for both single sound pulses and pulse sequences typical of searching or approaching bats. Neural adaptation was only evident in response to approaching bat sequences at high amplitudes, not search-phase sequences. These results show that, for short echolocation calls, a large range of sound levels cannot be coded by moth auditory receptor activity, resulting in no information about the distance of a bat, although differences in activity between ears might provide information about direction.

Post-release survival of hand-reared pipistrelle bats Pipistrellus spp)

There is very little known about the post-release survival of hand-reared pipistrelle bats Pipistrellus spp). We radio-tracked 12 pipistrelle bats, hand-reared and released under three different protocols: i) limited pre-release flight training and overwintering (n = 5); ii) prolonged pre-release flight training, but with limited space (n = 2) and iii) prolonged pre-release flight training in large flight cage (n = 5). Of the five bats reared under the first protocol, four were recovered, grounded, within 48 h and the signal from the fifth bat lost on day two, due either to tag failure or from the bat flying out of the study area. Both bats in the second group flew strongly on the night of release but on the second and third nights only one emerged and flew briefly. The signals from both bats remained stationary on subsequent nights. In contrast, bats from the third group were tracked for between five and ten nights, indicating that they were able to survive independently following release. These preliminary results suggest that post-release survival depends on extensive pre-release conditioning in a large flight cage, rather than the limited flight opportunities traditionally provided within domestic houses by bat carers. Other factors that may affect post-release survival are discussed and further work is encouraged to determine whether rehabilitated bats integrate with the local population.