In the bid to find a mate on the busy forest floor, it pays to be able to shout louder than the rest. But there is one type of amphibian, the adorably-named pumpkin toadlet, that whispers rather than yells. Now researchers have finally figured out why: the tiny tangerine dream is completely deaf.
There is actually such a thing as an earless frog, but counterintuitively, these amphibians can actually detect sound waves. The pumpkin toadlets, on the other hand, are apparently as deaf as a doorpost. Neither the males nor the females are able to hear the calls made by the fellas, which it is assumed are meant to attract mates and defend their territory, report researchers in Scientific Advances.
The inability of the tangerine toad to hear anything was discovered when herpetologist Dr Sandra Goutte traveled to Brazil’s Atlantic forest to determine how the amphibians hear their calls. The vocalizations are very low by frog standards, and there were questions as to how they heard each other over the din of the rainforest.
But as Goutte played the noises back to pumpkin toadlets in the forest, she was shocked by the lack of reaction. The frogs didn’t alter their behavior at all, and carried on as they were. They didn’t even position themselves towards the source of the call as would be expected. In a follow-up to this, laboratory testing confirmed that the teeny orange critters are totally deaf, and that the middle of the ear is vestigial, in the same way that hind legs are in some whales.
It seems an odd thing for the frog to do, continuing to chat away while there is no one to listen in. For one, drawing attention to yourself might be a costly behavior as it could attract birds or beasts wanting an easy snack. But then again the little frogs are hardly shrinking violets as the vivid orange amphibians strut around the forest floor. In fact, researchers think that their toxins are so potent they don’t actually have any natural predators.
But the vocalization is costly in other ways. It takes energy to make these noises, and if no one can hear you then that is energy wasted. The pumpkin toadlets communicate in other non-vocal ways, such as by waving their hands and gaping their mouths, so the researchers suggest that perhaps the important aspect of their squeaking is not the noise itself, but the movement of the throat.
It could be that this is actually a visual communication that has developed, and the buzzing noise is simply a by-product of this.