On Sálvora Island, off the coast of Spain, thousands of yellow-legged gulls dot the grassy cliffs from April to late July. It is a riot of white wings and plaintive calls. Occasionally, the chorus changes as the seabirds engage in courtship and chick-feeding. And when the adults notice a predator, such as a dusky-coated mink, the chorus shifts again, to a characteristic alarm call — ha-ha-ha.

These acoustic cues reach not just young and adult gulls but unhatched embryos, too. In 2018, researchers found that when gull eggs hatch, the ones that were exposed to alarm calls were able to crouch and hide from predators a couple of seconds faster than others.

A few other bird species, including quails, fairywrens and zebra finches, are known to relay similar cues about the environment to their unhatched young, to prepare hatchlings to fend for themselves.