The Animal as a Sound Source

Abstract Many animals use specific calls as ‘long distance communication signals’ for the attraction of a mate or in territorial defense. Such calls are in many cases loud enough to carry beyond the caller's home range or territory, and therefore can be detected and recorded without disturbing the caller. Such sound signals have certain properties in common with the electromagnetic signals of comparable wavelength, used in radio telemetry (geometry of spread, attenuation in the natural environment), and can be measured with comparable accuracy. The advantage of ‘acoustical telemetry’ is that the animal under investigation remains undisturbed (no trapping or handling), and limitations of transmitters (weight, life expectancy of batteries) do not apply. The disadvantage is that the particular time of measurement is beyond the observer's control. If, in a particular species, radio tracking is feasible, radio microphones can provide valuable information in addition to the location of the source: especially faint vocalizations used in close-contact communication can be observed continuously, and other selected activities, which are accompanied by sound (locomotion, breathing, feeding, digging, gnawing, etc.) can be recorded, yielding an intimate insight into behavior and behavioral time budgets.