An international team of researchers led by Cornell University and the Doñana Biological Station has documented a surprising phenomenon: bird species separated by thousands of kilometers and millions of years of evolution share a learned vocal signal to warn about the presence of brood parasites, such as cuckoos, which lay their eggs in the nests of other birds.
This finding, published in Nature Ecology and Evolution, represents the first known example of an animal vocalization learned from an innate response shared by multiple species, and offers new insights into how natural selection can shape vocal communication systems.
Brood Parasitism and Defensive Cooperation
The plaintive call appears in areas with high parasite pressure and fosters collaboration among birds.
Brood parasitism forces host species to raise foreign chicks, which can compromise the survival of their own offspring. Therefore, identifying and repelling parasites becomes a key evolutionary strategy.
The study reveals that more than 20 bird species across four continents emit an almost identical “whining” call when detecting a parasitic bird near their nests.
“The evolution of the plaintive call is affecting cooperative behavior patterns among birds worldwide,” explained James Kennerley, lead co-author.
Social Learning and Vocal Transmission
Although the call has an innate basis, birds learn it socially. When they hear the sound, they respond instinctively, but then observe the context and learn when to use it. This process, called social transmission, was described by Damián Blasi, a language scientist at Pompeu Fabra University.
“It is an intermediate point between instinctive vocalizations and fully learned units, like human words,” noted William Feeney, co-director of the study.
Evolutionary Implications and Theoretical Challenges
The study suggests that human language may have evolved by integrating innate and learned signals.
This discovery challenges the traditional division between animal communication and human language, by showing how a vocalization with mixed components can emerge in multiple species. The authors propose that human language could have evolved through the gradual integration of instinctive and learned elements, as anticipated by Charles Darwin.
“It’s like seeing how evolution allows for learned meanings to be assigned to innate sounds,” concluded Feeney.
A Universal Call in Complex Ecological Contexts
The vocalization appears in regions with dense networks of interaction between hosts and parasites.
Species that produce the call tend to live in areas where brood parasitism is common and where cooperation among birds is essential.
Communicating when and how to collaborate becomes essential for defending nests, which explains the vocal convergence among species that have never been in direct contact.
