Sea turtle embryos develop a complete enough ear to hear sounds shortly before they are ready to hatch. Researchers in Oaxaca, Mexico, placed recording instruments in nests to listen into and classify sounds coming from leatherback sea turtle eggs. The embryos created sound types of grunts, chirps, and complex hybrid tones that were only heard before any hatchlings had left their eggs. After some of the baby turtles pierced the eggs open and started digging their way out, the sounds in the nest changed. suggesting that sound communication helps the hatchlings coordinate their hatching so that they can come out of the nest in large groups.
This is not the first time sounds coming from the nest are discovered or used. For years, volunteers trying to rescue hatchlings from predators or light pollution have used stethoscopes to listen into the nests and predict when the hatchlings will come out. As sand is a very good insulator, this method can only be used to listen to sand-scratching sounds a few minutes before the hatchlings have reached the surface.
Identifying the sound patterns near the time of egg hatching opens new possibilities in sea turtle conservation. Sound sensors embedded in a nest can alert researchers when the hatchlings are about to emerge, allowing for adequate conservation actions at the right time. This will allow conservation groups to effectively monitor a larger number of nests without wasting costly resources and volunteers time.