The gleaning attacks of the northern long-eared bat, Myotis septentrionalis, are relatively inaudible to moths.
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This study empirically tests the prediction that the echolocation calls of gleaning insectivorous bats (short duration, high frequency, low intensity) are acoustically mismatched to the ears of noctuid moths and are less detectable than those of aerially hawking bats. We recorded auditory receptor cell action potentials elicited in underwing moths (Catocala spp.) by echolocation calls emitted during gleaning attacks by Myotis septentrionalis (the northern long-eared bat) and during flights by the aerial hawker Myotis lucifugus (the little brown bat). The moth ear responds inconsistently and with fewer action potentials to the echolocation calls emitted by the gleaner, a situation that worsened when the moth's ear was covered by its wing (mimicking a moth resting on a surface). Calls emitted by the aerial-hawking bat elicited a significantly stronger spiking response from the moth ear. Moths with their ears covered by their wings maintained their relative hearing sensitivity at their best frequency range, the range used by most aerial insectivorous bats, but showed a pronounced deafness in the frequency range typically employed by gleaning bats. Our results (1) support the prediction that the echolocation calls of gleaners are acoustically inconspicuous to the ears of moths (and presumably other nocturnal tympanate insects), leaving the moths particularly vulnerable to predation, and (2) suggest that gleaners gain a foraging advantage against eared prey.
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