Birds of different species can understand each other’s alarm calls warning of cuckoos.
Brood parasites such as cuckoos lay their eggs in other birds’ nests, tricking the hosts into caring for their offspring at the expense of their own.
Research found that 21 bird species across four continents all make similar “whining” vocalizations when they spot a brood parasite, and when played recordings of other species’ calls, they all recognize them and react by mobbing the invader.
One researcher told New Scientist that the calls, referring to external objects in the world rather than internal states such as fear or excitement, “could be the first stepping stone towards language” and that animal communication and human language were on a spectrum.