THE ENERGETICS OF ACOUSTIC SIGNALING IN ANURANS AND INSECTS

This review focuses on the energetics of advertisement calls in frogs and insects (mostly ensiferans). I also review a number of methodological questions relating to the most appropriate ways to normalize metabolic rates for calling animals and to calculate efficiency of sound production. Although the mechanism of sound production is very different in these groups (vocalization vs. stridulation), net metabolic costs normalized to mass are similar among species producing the most conspicuous calls. Features of the call that interact to determine energetic cost include repetition rate, call duration, and intensity (sound pressure level). Anurans tend to produce louder (more intense) calls while ensiferans tend to produce sound during a greater proportion of the calling bout. All evidence suggests that advertisement calls are produced aerobically and the aerobic costs are similar or exceed the aerobic (but not necessarily total costs) of terrestrial locomotion. The pattern of radiated sound tends to be constant within a species and can be predicted to some degree from characteristics of an animal's acoustic radiator. Efficiency of sound production (acoustic power/net metabolic power) is low (0.05 to 6%) and variable when compared to locomotion (similar to 10-20%). From the present sample it appears that frogs are more efficient than ensiferans, but as more katydids are studied this trend may not hold. Of the factors that have been identified as determining efficiency the most important are the match between the size of the radiator and wavelength radiated, the absorption properties of the environment immediately around the animal, and the presence or absence of structures such as baffles and acoustic burrows.