The fledglings of some bird species such as Greater Flamingos, Royal and Sandwich Terns, eiders, ostriches, and a number of penguins separate from their parents and form a group, or "creche." Whether parents continue to feed their own chicks, or the chicks feed themselves, supervision of the creche (when it occurs) is usually delegated to a small number of guardians. The guardians, of course, are related to only a small number of the young in the group. It is curious that "altruistic" guarding of unrelated young, presumably a dangerous, tiring responsibility, has evolved. Upon closer scrutiny, however, the behavior is not as altruistic as it appears.

Chick-creching generally occurs among birds that breed in large, loose colonies and whose eggs all hatch at about the same time. The day-care system permits a fledgling to lose itself in a crowd and reduce its risk of predation (dilution principle). In the case of young remaining dependent on their parents for food, creching frees the adults to spend more time foraging. Evolutionary theory suggests that creching is likely to develop when the young reared in a gang have a better chance of surviving than those reared alone, so that the birds practicing creche formation contribute more of their genes to the next generation than those that do not form creches.

It is not so easy, however, to predict which adults will adopt guarding behavior. In some species, this role is taken by nonbreeding adults (occasionally "aunts," or adults whose broods were lost, etc.), but in others, such as African ostriches, dominant pairs compete for the opportunity to gather the young of others to their group. Such herding of young is reminiscent of an African catfish that gathers the offspring of cichlid fishes into a school of its own young. The little cichlids are kept to the outside, where they (rather than the young of the catfish) are the first to be discovered by predators. Data are needed on relative position and mortality of adopted offspring in relation to the chicks most closely related to the adults guarding the creche to determine whether such supervision is truly altruistic.

SEE: Parental Care; Parent-Chick Recognition in Colonial Nesters.

Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.