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
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
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.
Parent-Chick Recognition in Colonial Nesters.
Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.