[Illustration]
For long it has been written that the male hornbill walled up his mate
in her nest in a hole in a tree at nesting time, and one author even
wrote that the male plucked out the female's feathers at this time.
The facts underlying these statements have different interpretations,
but the nesting of the hornbill is still one of the most extraordinary
of animal habits. Travelers and naturalists in Africa had brought back
tantalizing bits of information, to add piecemeal to our knowledge of
these birds. Now all this is synthesized and corrected by R. E. Moreau,
onetime resident in East Africa, who made a study of certain species,
raised young birds by hand, and gave us a comparative study of their
behavior. Even this study must be considered preliminary, for, of the
twenty-six African species, we have breeding data on only sixteen of
them.
First we must not generalize too far as to "the hornbills," for there
are Asiatic and Malayan species as well as African, and African species
differ among themselves, the ground hornbill being especially aberrant
in its habits.
It is quite true that in many African species the female is walled up
in her nest, and the period when she is enclosed may last three to
four months. But it cannot be interpreted as an imprisonment forced on
her by the male, and presumably she could, if she wanted to, open the
entrance at any time, as she does finally on emerging.
Among the African species the details vary, but the nest is usually
located in a hole in a tree, and except in the case of the ground
hornbill the entrance is plastered up so that only a narrow slit is
left, about wide enough for the passage of the bird's bill. The female
takes an active part in the walling up of the opening, and might be
said to wall herself in. When the opening to be filled in is wide, the
male may bring earth, which he mixes with saliva in his gullet, and
presents to the female, who does the actual plastering. In some species
the walling up of the entrance may take months.
The female may wall herself in some days before she lays her first egg.
Throughout incubation she remains there. Depending on the species, she
may peck her way out, or burst out when the young are partly grown, or
she may stay until the young are ready to fly.
During the time the female is walled in the male brings food for her,
and later for the young, also. That he is a good provider is indicated
by the fatness of the female and her young. This is proverbial with the
natives of Africa. The method of feeding varies with the species. The
male may bring a bit of food in its bill, pass it in to the female,
and then go for another, or in other species we might think more
intelligent, the male carries a quantity of berries in its gullet, and
these are regurgitated one by one and passed to the waiting female;
such species make trips to the nest less frequently.
Apparently shortly after the female goes into the retirement of her
walled-in nest, she molts all her flight feathers, so that she is
flightless, and then begins to grow them again.
When the female bursts out of the nest with the young only partly
grown, the young that remain in a still very undeveloped state in the
nest, using material in the nest such as remains of food and rotten
wood, replaster the hole! The young, perhaps only halfway through their
fledgling period, wall themselves in! The female then helps the male
care for the young.
Such is an outline of what some of the African hornbills do at nesting
time. The habit is unique in the bird world. One species appears not to
wall up its nest. In an Asiatic species it is said that if the male is
killed other hornbills help to feed the female in retirement. The whole
procedure is an amazing behavior pattern, and one for the development
of which it is difficult to find a functional explanation.