An Australian song bird uses secret passwords to prevent identity theft, scientists have learned.
When they are still in the egg, superb fairy wrens learn a unique single note sung by their mother. Once hatched, they have to include the password within their begging calls in order to be fed.
Researchers found that the begging calls of fairy wren chicks differed from one nest to another.
Mother wrens also taught their mates the password, as well as trusted helpers, by singing a "solicitation song" away from the nest. The system is believed to have evolved to prevent identity theft by cuckoos.
Parasitic cuckoos typically lay an egg in another bird's nest which hatches early. The young cuckoo throws out the other eggs or chicks and takes over the nest, being fed and raised by the unsuspecting parents. In the case of the superb fairy wren, an invading cuckoo that does not produce the necessary password after hatching is likely to find itself abandoned.
"Parents and others attending the nestlings will only feed them if their begging calls contain the learned password," said study leader Dr Sonia Kleindorfer, from the University of Adelaide in Australia.
Studies showed that when clutches of eggs were swapped between nests, newly hatched chicks produced begging calls that matched those of their foster mothers. This was evidence that the passwords were learned.
The researchers were able to prevent attending parents feeding their young by playing the wrong begging call from a loudspeaker under the nest.
Reporting their findings in the journal Current Biology, they wrote: "Playback experiments showed that adults respond to the begging calls of offspring hatched in their own nest and respond less to calls of other wren or cuckoo nestlings.
"We conclude that wrens use a parent-specific password learned embryonically to shape call similarity with their own young and thereby detect foreign cuckoo nestlings."