The relationships between echolocation calls, morphology and diet in insectivorous bats

In this study we explored quantitatively the relationships between the size of bats, the frequencies in their echolocation calls, and the incidence of moths and beetles in their diets. We focused on the predictions of the all otonic frequency hypothesis which states that some insectivorous bats incre ase their access to moths that can hear echolocation calls by shifting to f requencies to which the ears of these insects are less sensitive. The hypot hesis predicts that the frequencies dominating the echolocation calls of ba ts may be correlated with the incidence of moths in their diets. We collect ed data for 62 species of bats that take airborne prey, usually flying inse cts, 25 species of high duty cycle echolocating bats (Rhinolophidae and Hip posideridae) and 37 species that are low duty cycle echolocators (Vespertil ionidae and Molossidae). For bats whose echolocation calls are dominated by frequencies < 100 kHz our regression analyses showed a parabolic dependenc y between moth consumption (% volume or % frequency) and echolocation call frequency (kHz), supporting the allotonic frequency hypothesis. The use of echolocation calls dominated by frequencies outside the range of best heari ng by moths may indeed increase the availability of these insects to the ba ts. However, when the same analysis was performed with only the bat species using echolocation calls dominated by sounds >100 kHz, the relationship wa s not statistically significant, suggesting that morphological characterist ics rather than echolocation call frequency may limit the range of potentia l prey items. Our analyses also demonstrate the importance of jaw morpholog y as a predictor of the incidence of beetles or moths in the diets of bats, and reveal that generally bigger species (as defined by forearm length) us e echolocation calls dominated by lower frequencies than smaller species. I n both high duty and low duty cycle echolocating bats the relationship betw een body size and dominant call frequency was best described by a linear mo del. We also propose that perch hunting was central in the development of t he high duty cycle approach to echolocation.