If a frog cries in the forest, sometimes even the frog can’t hear it. Such is the sad fate of two species of pumpkin toadlets—Brachycephalus ephippium and B. pitanga—that live in Brazil’s Atlantic Forest. Frogs and toads usually rely on sounds to find mates, and their ears are tuned to pick up the particular frequencies emitted by their own species. But the two pumpkin toadlets, small frogs about 1.5 centimeters long, couldn’t hear their own high-frequency vocalizations when researchers played their calls back to them in the wild, a team of biologists reported last week in Scientific Reports.
To find out what was going on, the researchers conducted hearing sensitivity tests in the lab, which revealed that the frogs’ brains didn’t respond to the mating calls. Dissection revealed that the frogs’ ears were underdeveloped, similar to several species of salamanders and eels that cannot produce vocal sounds. This is the only known example of an animal not being able to hear its own mating calls, and scientists suspect the frogs preserved their singing ability because it provides potential mates with visual cues, like the movement of their vocal sacs. And what about predators? Ground-foraging birds like guans can still hear the frogs’ calls. But the frogs’ bright colors—advertising their toxicity—are apparently enough to warn off the predators.