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Female frogs limit the length of male mating calls

Female túngara frog and frog-eating bat approaching a calling male, photos not to scale. [Image courtesy of A. Baugh, K. Lampert, A. Lang and M. O'Mara]

Male túngara frogs are known for their long mating calls, which they use in hopes of attracting a female. But, a new study shows that a long-winded frog song doesn't necessarily guarantee the males a mate. Instead, it seems that the female túngara frog's perception—or what she hears from her environment—is just as important as what the males are singing to her.

Karin Akre and colleagues studied these male mating calls of the túngara frog and found that the female frogs who love them—as well as the bats who eat the frogs—only listen to them for so long. Then, they make their move, even if the males aren't finished singing yet.

These findings are published in the 5 August issue of Science.

The frogs' mating calls include a whine followed by a series of grunts, or "chucks." So, the researchers played different túngara frog songs to female frogs and frog-eating bats on a stereo in order to see which speaker the creatures approached. Surprisingly, Akre and her team observed that the female frogs and the bats did not always go toward the speaker producing the most "chucks." Instead, their preference seemed to depend upon the ratio between "chucks."

For example, female túngara frogs always preferred two "chucks" to one. But, they didn't always prefer three "chucks" to two.

These findings suggest that female frogs, who are in a hurry to mate before becoming a bat's dinner, are forced to choose quickly. Akre and her colleagues suggest that female frogs become less choosy as the males' songs get longer, simply because it becomes harder to tell the difference between two songs as they both increase in length.

In light of these findings, the researchers say that a female frog might discriminate between mating calls only when there is a significant difference in "chucks," and when detecting a difference between two songs is easy. The researchers' findings also suggest that female frogs (and frog-eating bats) help to limit the length of male mating calls, so that they don't become too elaborate over time.