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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
siggnal-to-noise ratio was +1.5 dB or lower.
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By taking the distributuion 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.
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