'Empty Nester' Parent Birds Use Recruitment Calls To Extend Offspring Care

It is well known that birds feed their young directly, but it is usually assumed that care ends when the young leave the nest and begin to forage for themselves. In many species, however, parents and young continue to associate with one another beyond this point of nutritional independence. Because juveniles are poor foragers, they might benefit from staying close to experienced adults, who can find the best feeding sites.

The new study shows that adult babblers continue to care for their young during this period. By observing the birds closely and performing simple playback and feeding experiments, the biologists found that babbler adults use a special "purr" call to recruit inexperienced fledglings to rich, divisible food sources (adults responding to the calls often met with aggression from the caller). The researchers found that fledglings that responded to this call were much more successful than those sticking to areas chosen by themselves. This work shows that recruitment calls by adult birds may prolong offspring care beyond the onset of nutritional independence, and it sheds new light on the sophistication of parental care among birds.

The researchers include Andrew N. Radford of the University of Cambridge in Cambridge, United Kingdom; Amanda R. Ridley of the University of Cape Town in Rondebosch, South Africa.

A.N.R. was funded by an Association for the Study of Animal Behaviour research grant and a Junior Research Fellowship from Girton College, Cambridge. A.R.R. was funded by a Travelling Research Fellowship from Newnham College, Cambridge and by the Percy FitzPatrick Institute of Africian Ornithology Centre of Excellence, University of Cape Town.