Evolution of the highest sound pressure levels in mammalian echolocation calls

Abstract

Recent work has shown that for some echolocating bat species there is a physical limit to the loudness of their echolocation signals, and this idea has been extended to suggest there is a physical limit to the loudness of echolocation signals of all species. This is at odds with the assumption that the loudness of a species call is driven by their body size, where louder species are larger species. This is also at odds with the prey detection hypothesis, where for echolocation calls the successful detection of prey at size extremes (both minima and maxima) drives the loudness of echolocation calls. A physical limit of loudness in echolocation calls may exist, but this has not been explored using comparative analysis. We compare the loudest echolocation calls across 63 echolocating mammals (including almost half of all aquatic echolocators) and show the assertion of a physical limit to loudness exists for bats in terrestrial habitats but breaks down for odontocetes in aquatic habitats. For aquatic echolocators, the loudness of their echolocation calls scales with body mass. We examine evolutionary and ecological pressures which may have led to these differences, and their influence on echolocation loudness.