[Illustration]
In many a well-run American home the children have definite
responsibilities, the older children may help look after the younger,
and even grown-up relatives may stay as part of the family group. As in
so many cases there may be found parallels to this in the bird world.
The ani, the curious tropical American cuckoo that makes communal
nests, is gregarious and the young of the first brood become part of
the parent flock. Two more broods may be raised during one season
in Cuba, and the young of the earlier brood may feed their younger
brothers and sisters of the later brood. The same has been recorded
for many other species in the wild: in eastern bluebirds, mountain
bluebirds, wheatears, long-tailed titmice, barn swallows, coots, rails,
and gallinules young have been recorded as feeding still younger birds.
In captivity this habit has been seen a number of times. Young birds
hardly able to feed themselves may help feed still younger individuals
of the same or other species, and a nestling crowned hornbill has been
seen to offer food to its nestmates. This tendency to feed nestmates
evidently appears very early in the life of the bird, as Dr. C. O.
Whitman, who worked intensively with pigeons at the University of
Chicago, recorded a hybrid dove only twelve days old that fed its
nestmate.
FIVE JAYS AT A NEST It was rather generally known that occasionally
more than the two parent birds attended a nest, but until 1935, when
Alexander Skutch, the authority on the biology of Central American
birds, published his paper "Helpers at the Nest," few of us realized
how widespread this was. Since most birds of a species are difficult to
identify individually, one must actually see the extra, unmated helpers
at the nest along with the parents to be sure they are there. In the
brown jays of Central America that Skutch studied closely the colors of
the soft parts, bill, feet, and eye rings were variable and he was able
to recognize many individual birds. At five nests he watched he found
at least one helper at each nest, and at one there were five helpers,
all bringing food. Sometimes, if between an incoming, food-laden bird
and the young, they would take the food and pass it on to the nestling.
At one nest the unmated helper was more zealous in guarding the nest
than were the rightful parents. Sometimes, perhaps, these helpers were
unmated young of the parents' previous year's brood, but this could
hardly have been the case where there were five helpers, for the brown
jay ordinarily raises no more than three young a year. A black-eared
bush tit of Central America seems to have a great preponderance of
males and at one nest in addition to the parents there were three other
males bringing food to the young.
MATERNAL PENGUINS Perhaps the most striking example among birds is
the emperor penguin. These birds breed in the dark and cold of the
antarctic winter, on the edge of the ice shelf. The single egg is
carried on the feet of the brooding bird; indeed one wonders what other
adaptation for holding the egg would be possible in this land of ice,
snow, and water. Only a few of the adults in each colony lay eggs any
year, perhaps one in five, or one in twelve. But all the adults in
the colony have the urge to incubate and brood. Thus many old birds,
rather than merely the two parents, may take turns caring for each egg
or chick, leaving the rest ample time to feed. So strong is the urge
to brood that struggles may take place over a chick and it may be very
roughly handled. Indeed the chicks may so resent this that they may
creep away into ice crevices and freeze to death. Another strange turn
this behavior may take is that frozen eggs, dead chicks, and even bumps
of ice of suitable size are carried on the feet and covered with the
birds' feathers by their "would-be fathers and mothers."