Acoustic interference limits call detection in a Neotropical frog Hyla ebraccata

Problems associated with communication in noisy environments include detection, discrimination, and localization of appropriate signals. I investigated the effects of broadband background noise on call detection by female Hyla ebraccata, a Neotropical treefrog. In playback experiments, I offered females a choice between two stimuli: chorus noise alone or chorus noise plus a computer-synthesized call. By systematically increasing the level of chorus noise, I determined that females could no longer reliably choose between the two speakers when the signal-to-noise ratio was +1.5 dB or lower. By taking the distribution of calling males into account, I estimated that females detect only the nearest male. If a female were to sample more than a very few males, she would need to move around the chorus. By doing so, she probably increases the costs of mate choice. Thus, the noise of a chorus impairs the ability of females to detect conspecific calls and thereby limits their ability to choose between mates. These limitations could have serious implications for the evolution of signallers' and receivers' behaviour. (C) 1999 The Association for the Study of Animal Behaviour.