Why do predators and parasites eavesdropping on mating signals of their prey preferentially attack individuals producing certain types of call? Predators could use information encoded in calls to decide whom to attack.
Researchers from the University of Texas at Austin and the Smithsonian Tropical Research Institute explored the mechanisms driving such signal preferences in predators and parasites that use túngara frog mating calls to find their prey. Their research appears in the March issue of the American Naturalist.
Male túngara frogs produce two types of calls to attract females: simple calls that consist of frequency-modulated sweeps called "whines" and complex calls that consist of whines followed by short, broadband secondary components called "chucks." Female túngara frogs, as well as unintended receivers such as frog-eating bats and blood-sucking flies, prefer complex to simple mating calls.
Bernal, Page, Rand, and Ryan tested whether bats and flies prefer complex calls because they indicate higher quality males and/or higher male density. The authors found that call complexity is not correlated with the frogs' length, mass, or body condition, and thus does not signal their quality. Complex calls, however, indicate higher abundance of prey/host. Thus increased effectiveness of attack may have played a role favoring the preference for complex calls in eavesdroppers.
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Ximena E. Bernal, Rachel A. Page, A. Stanley Rand, and Michael J. Ryan, "Cues for eavesdroppers: do frog calls indicate prey density and quality?" American Naturalist 169:409-415.
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