Birds of a feather have been known to flock together—even before they’re born. A new study shows that unhatched yellow-legged gulls can vibrate their egg shells, warning their siblings of danger, The Scientist reports. Researchers exposed a group of gull eggs to recordings of the harsh cry their parents emit when threatened. After hearing the sound, 30 eggs began to quake and made other, unexposed eggs shake when placed next to them. A control group exposed to recordings of white noise did not vibrate. These vibrations may be important for siblings to communicate warnings from their parents, even if some chicks have not yet developed a sense of hearing, the researchers write this week in Nature Ecology & Evolution. Scientists have known for some time that embryos can communicate from inside the egg, but this is the first instance of an embryo using outside information to warn its siblings of predators.
*Correction, 5 August, 11:45 a.m.: This article has been updated to reflect that this is not the first instance of embryo-to-embryo communication, but rather, the first instance of embryos warning about predation.