Frog's love call beckons predators, too

A frog's evening serenade beckons his would-be suitors but also summons competition from rivals and attracts predators, making dating a dangerous endeavor, international researchers said Thursday. The tiny brown tungara frog, found in Central and South America, seeks out females by perching in a shallow pond and making a unique mating call that comes out as a series of whines and "chuck" sounds. A large vocal sac under his mouth inflates and deflates as he calls, causing ripples in the water. Researchers from the United States, the Netherlands and Panama decided to study how these ripples affected competition among frogs and predation by local bats that eat frogs. They found that mating calls accompanied by ripples tended to arouse more competitive calls from nearby male frogs than calls that were sent out without making waves. They also discovered that bats were using their own biological sonar abilities to find frogs in the dark via the pond ripples. Although the frogs have learned to stop calling if they glimpse a bat overhead, the tactic usually comes too late. "Unfortunately for the frog, the water ripples created by his call do not also stop immediately," said lead author Wouter Halfwerk, a postdoctoral researcher at University of Texas at Austin. "The ripples continue to emanate out for several seconds, creating a watery bull's-eye on the frog. Bats use the ripples, thereby beating the anti-predator strategy." However, bats lose their advantage if the frog makes his mating calls from an area cluttered with leaves, which stop the ripples from spreading. The study appears in the US journal Science, and included researchers from UT Austin, the Smithsonian Tropical Research Institute in Panama, Leiden University in The Netherlands and Salisbury University in Maryland.