Secret 'password' helps young birds not to breed other chicks

Brood parasites lay their eggs in the nests of other birds, leaving them to raise their chicks, but host birds are not easily fooled as they teach their young ones a secret 'password' that helps them decide whether the chicks were their own, a study shows.

Female superb fairy-wrens teach their embryos a "password" while they are still in their eggs through incubation calls containing a unique acoustic element.

After they hatch, fairy-wren chicks incorporate this unique element into their begging calls to ask for food.

Chicks whose begging calls most resembled their mothers' incubation calls received more food, the findings showed.

In the new study, researchers looked at the relationship between superb fairy-wrens and Horsfield's bronze-cuckoos to see if a greater threat of brood parasitism would cause the fairy-wren to up its teaching efforts.

"We show a mechanism that starts in the nest and involves active teaching and sensorimotor learning in embryos," Diane Colombelli-Negrel and Sonia Kleindorfer from Flinders University in Australia were quoted as saying.

First, the researchers recorded calls from 17 fairy-wren nests in South Australia.

They found the similarity between the mother's password and the chick's begging call was predicted by the number of incubation calls produced by the mother, Wired.com reported.