The nestlings of fairy-wrens don’t have much of a choice when it comes to listening to their mothers: The birds must reproduce a particular sound learned from their moms to be fed, according to a study published Thursday in the journal Current Biology.
The researchers, led by Sonia Kleindorfer of Flinders University in Australia, call the sound the bird’s “learned password.”
The team discovered the remarkable mother-chick ritual by chance when they noticed that the mothers were aiming calls at their eggs well before they hatched. So they set out to determine why. First, the researchers realized that the call made by the nestlings in order to be fed was different in each nest, suggesting it might be learned.
The pieces began to come together when the team also observed that each nest’s begging call — the password the nestlings need — was contained within the call that the mothers made to their unhatched eggs. In order to prove that the chicks were learning the sound from their moms rather than the song being innate, Kleindorfer and her team swapped the eggs from two different nests. Once hatched, the chicks produced the begging call of their foster moms, not their birth moms, proof the call was in fact learned in the egg.