Turtles are generally thought of as silent creatures, but recent evidence has emerged that at least 47 turtle species make some form of sound. Those sounds communicate various messages, from social standings to reproductive signals. But it's not just adult turtles who are speaking their minds. It turns out babies, too, make sounds - even before they hatch from their eggs.

Researchers from Brazil, Mexico and the US got together to study the nests of 12 leatherback sea turtle nests in Oaxaca, Mexico. Starting on day 51, the point at which the babies's ears should be developed enough to hear sounds, they monitored the nests for any signs of noise. They immediately began detecting sounds, recording more than 300 different noises in total. They classified the sounds into four categories, including chirps, grunts and "complex hybrid tones," or sounds composed of two parts that they classified as pulse characteristics and harmonic frequency bands.

That latter sound - the most complex of the bunch - was only recorded in nests that contained just eggs, rather than eggs and hatchlings (most had begun hatching by day 55). The baby turtles, the researchers believe, may be coordinating their hatching timing by emitting the sounds. This phenomenon has been observed in other animals ranging from birds to crocodiles, likely as a survival mechanism. In the case of the turtles, hatching en masse brings a certain strength in numbers. While some babies will be picked off by predators, a bird can only eat so many sea turtles at a time, meaning at least a few will make it to the sea.

This finding, the authors point out, means that light pollution might not be the only anthropogenic nuisance threatening baby sea turtle survival. Noise pollution could be affecting them, too.