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 they 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.
“This work changes our understanding of the pre-natal environment in birds,” says Dr Rebecca Kilner, who led the research. “We’ve known for about twenty years that maternal substances in the egg can influence the way in which chicks develop, but the common assumption is that they are a way in 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 penalized directly rather than the mother”.
The work was funded by the Natural Environment Research Council.