A recent study has found that Superb Fairy-wren mothers teach a "password" to their young while they are still in the egg as a means of identifying them and detecting intruder nestlings.

"Parents and others attending the nestlings will only feed them if their begging calls contain the learned password," says co-author of the study published in journal Cell Biology, Professor Sonia Kleindorfer of Flinders University in Adelaide, (as reported on the ABC Science web site).

Otherwise, the parents simply abandon the nest and start again. Kleindorfer says it is the first time prenatal learning has been uncovered in birds.

While analysing sound and video footage from a series of Fairy-wren nests in the South Australian wild, the researchers noticed the Fairy-wren mothers appeared to be singing to their unhatched eggs.

Kleindorfer says the female would call repeatedly - often as much as 15 times an hour. "We then found when the nestlings hatched the chicks had a one-note begging call," says Kleindorfer. An analysis of the mother's "incubation call" showed it contained this begging note used by the chicks.

The researchers also determined that each nest had a different "password".

To determine if the trait was genetic or learned, the team then swapped eggs between 22 nests. In swapped nests the chicks cry was more similar to its foster mother than biological mother, Kleindorfer says, indicating the trait is learned.

She says the feeding password plays an important role in helping Fairy-wren mothers identify the chicks of parasitic birds such as cuckoos that abandon their parenting role by laying their eggs in the Fairy-wren's nest.

The cuckoo chicks hatch earlier and monopolise their new parents by ejecting rival Fairy-wren siblings eggs from the nest. However the "password" helps the Fairy-wren mother identify her chicks and reject the home invader as she begins "teaching" her chicks the feeding call about 10 days after the eggs are laid.

Cuckoo chicks begin hatching about one day later whereas the Fairy-wren chicks have another four to five days in the egg.

Kleindorfer says this means the parasitic cuckoo chick does not have time to learn the feeding call.

Read the full article at http://www.abc.net.au/science/articles/2012/11/09/3629195.htm