Researchers discovered why Panama’s tiny tungara frogs adapt their mating calls in urban areas, which serves as an example of how animals adapt their communication strategies to human development.
In Panama City, tungara frogs can be found everywhere from ditches and puddles in neighborhoods on the outskirts of the city, to drains in the city center. Every evening at sunset, the 1-inch male frogs crawl into puddles to serenade the ladies, who listen discerningly, selecting a mate based largely on his love song.
Tungara frogs don’t croak like American bullfrogs. Wouter Halfwerk, assistant professor at Vrije University in Amsterdam and team leader of the study, describes the sound as:
In urban areas, the male frogs sing longer, more complex love songs, taking advantage of the relative absence of eavesdropping predators, like bats and flies. These fancy urban love songs are 3x more likely to attract females than the shorter, simpler rainforest songs. But they’re also more likely to attract predators, where there are any. That’s why, in the more biodiverse forests, frogs keep their songs short — to extend their lives.
In a series of experiments, Halfwerk’s team played recordings of calls in various urban and forest locations and recorded the number of approaching females, predators and parasites using remote, infrared-sensitive cameras. The results were published in the journal Nature Ecology & Evolution.
In the city, the calls did not attract any bats, and only a few flies. But they also attracted a fewer number of females per call, suggesting that males had to work harder to get the ladies to pay attention.
Next, the researchers recorded up to a hundred calling males at the same sites and played them back for forty females, from two speakers. Thirty of the forty hopped over to the speaker playing the more complex and conspicuous urban calls.
Halfwerk’s team also studied how quickly the tungara frogs adapted their calls. When they moved urban frogs to forests, the males instantly simplified their calls to avoid bats and bugs. But when forest males got to cities, they didn’t immediately croon with more complexity.
Unfortunately, amphibian populations are declining worldwide, mostly due to habitat destruction. Tungara frogs are a rare example of an animal adapting, evolutionarily, to new circumstances. "Just as we change our social relationships in cities, animals are changing their relationships and their behavior in the radically altered biological communities we are creating across the globe," concluded Rachel Page, a co-author of the paper.