By changing conditions within the egg, canary mothers leave a message for their developing chicks about the life they will face after birth. In response, nestlings adjust the development of their begging behaviour.

If chicks get a message that they will be reared by generous parents then they beg more vigorously for food after hatching. But chicks that are destined to be raised by meaner parents end up being much less demanding.

By attending to messages in the egg, nestlings gain weight more rapidly because they match their demands to the parents' supply of food, and can avoid either begging too little or wasting effort on unrewarded begging.

The Cambridge team made the discovery using fostering experiments, exchanging eggs between canaries' nests so that the chicks grew up in an environment that they were not expecting.

"This work changes our understanding of the pre-natal environment in birds," says Dr Rebecca Kilner of the University of Cambridge, who led the research.

"We've known for about twenty years that maternal substances in the egg can influence how chicks develop, but the common assumption is that they are a means by which mothers manipulate their offspring in a way that suits the mother more than the chick.

"What we've shown is the reverse: these substances are actually there to suit the chick. If we muck up the message in the egg experimentally, it is the chick that is penalised directly rather than the mother."

The work was funded by the Natural Environment Research Council, and is published in Science on March 12, 2010.

Note: If no author is given, the source is cited instead.

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