NIDIFICATION is nest-building: that is, the process and practice of arranging or constructing a place for the deposit and protection of eggs and of the young hatched therefrom as long as required by the circumstances of each case. The membranous or glutinous packets in which the eggs of many of the higher worms, mollusks, of some insects, and even of most amphibians (frogs and salamanders, for example) are enclosed, coincident with their voidance by the female, may not be included, because they are not prepared by the mother, but are as natural products as the eggs themselves. Insects and spiders put their eggs in places of safety, or where the young, when they come, will be close to their proper food. When not buried in some way they may be protected by some sort of covering, but this is about all until we come to the highest group — the ants, wasps and bees. The larvae of insects, however, construct for themselves many and sometimes very remarkable abiding-places, which are certainly “nests” in the broader sense of the term, since they are the shelters within which juvenile growth and transformations, often much prolonged, are carried on; but it is not proper to include mere pupa-cases, such as the cocoons of moths. Thus the white, silken webs that disfigure and injure our fruit-trees are spun by a colony of caterpillars, and form their nest, to which they return nightly after feeding; finally, however, each caterpillar wraps a cocoon about him and sinks into the pupal inertia for the winter, and this wrapping is in no sense a nest. Some insects, however, do make definite homes for eggs and expected young. The most striking examples are found among the wasps and bees, both social and solitary, and the ants, the last-named forming regular nurseries in their colony-habitations, and caring for their larvae as do the most intelligent mammals for their young. Sufficient details to illustrate these and other cases of insect nidification may be found in the articles Ant; Bee; Insect; Moth; Wasp, etc. The clearest illustration, probably, is afforded by the common brown wasps (Polistes) that make individual paper nests, shaped like inverted wine-glasses, hung by a short stem; they are very often attached to the ceilings of sheds, barn-lofts and the porches of rural houses. These begin with a single cell made in early warm weather by a female wasp that has survived the winter. In this cell she lays a fertile egg, and then proceeds diligently to add other cells around this until finally half a dozen circles have been fashioned. Meanwhile the eggs in the central, first-made cells, have hatched and the grubs grow and must be fed. As they increase, the cells are lengthened, and constant nourishment is given by the busy mother, until finally the earliest grubs escape as mature wasps and begin to help in the care of the rapidly increasing family. This is a real nest.
The examples of nidification among fishes are related in considerable detail in the article Fishes, Nest-making by.
Among the salamanders, newts, toads, frogs and other amphibia, the eggs are usually inclosed in some sort of gelatinous envelope and laid in the water, in most cases without any particular care, and in others are attached to stones or plants, and probably guarded by the parent. Some newts and frogs coil about or carry the eggs; or, as in the case of the well-known Surinam toad, the eggs are voided from the protruding and turned-up oviduct of the female in such a way that the male, perched on her back, squeezes them into the spongy surface of her back, where they mature in little pockets. Some Eastern frogs and many of the South American tree-frogs have similar devices, but only one makes what might be called a nest. This is the ferreiro or “smith” (Hyla faber) of Brazil, which digs up mud in its ponds, and builds around a chosen space a strong wall reaching to, or a little above, the surface of the water. This is done at night by the female, who pats the wall into a firm rampart; and here she lays her eggs, the tadpoles thus hatching and growing in security until able to escape and take care of themselves.
The reptiles in many cases (among snakes and lizards) bring forth their young alive, and when they care for them do so without any previous preparation. The pythons (q.v.) coil around their eggs and thus protect and incubate them. Many snakes worm their way into loose soil or rotting dung-heaps, and leave their eggs to chance. The chameleons and many other lizards scrape a hole in the mold and cover up the eggs left there. That is also the method of the turtles, but they are more careful, for while some simply dig a cavity in the sand of the sea-beach or river-bank, deposit their eggs and cover them up, others take great pains to pack the earth down hard. The well-known green turtle searches long and carefully before she satisfies herself that the spot is suitable, and then digs with her flippers a hole three feet deep, in which she deposits about 200 eggs. The hole is then filled up, and the top leveled off until little or no trace of the operation is visible. That is the practice of the Old World crocodiles, also the gharial, or gangetic crocodile which varies it by burying its eggs deeply in two layers, with a thick layer of sand between them. Our American alligators, however, make much more elaborate preparations for their young as is described under Alligator.
Birds, of course, furnish the most typical examples of nest-building and of all the other phenomena of nidification, often on a scale that compels wonder at the ingenuity and beauty displayed. See Birds, Nests of.
Nidification, among mammals, involves a
wider use of the term than with birds, at least,
and may be defined as any living-place
constructed by the animal and formed more or less
like a bird's nest. A striking instance is
afforded by the habits of the big anthropoid
apes — the gorilla, orang-utan and the chimpanzee.
All of these, in a very similar manner,
construct platforms of broken branches in trees,
upon which to sleep, where the females bring
forth and nourish their young. Sir James
Brooke, in his ‘Ten Years in Sarawak,’ says
that in the case of the orang-utan, the nest is
always built low down, often within 25 feet
of the ground, and is three or four feet in
diameter and quite flat on top. The Australian
bandicoots form compact nests of grass in a
shallow hole in the ground, and our American
opossums in a hollow log, or broken tree-trunk.
The cony (Hyrax) of South Africa, and our
cony (Ochotona), make warm winter-nests
within the interstices of loose rocks, and some
African lemurs bed-chambers of sticks and
leaves in the tree-tops. The chief mammalian
nest-builders, however, are found among the
arboreal squirrels and the rats and mice of
various parts of the world. The European
dormouse is an excellent example. The British
squirrel forms a nest, “constructed,” says Bell
(‘British Quadrupeda,’ 1839), “in a very intricate
and beautiful manner, of moss, leaves and
fibres curiously interlaced; and it is usually
placed either in a hole in a tree, or in a fork
between two branches, often where it can with
difficulty be distinguished from the tree itself.”
Our American rodents have similar habits. The
flying squirrels of this country form thick warm
beds of feathers, hair or other soft materials
in abandoned woodpecker-holes and other crannies.
Our common gray and fox squirrels,
which spend the winter in well-bedded chambers
in tree-holes, construct in summer large nests
of leaves and leafy twigs, massed together in
tree-tops, into which they bore their way, then,
by crowding and biting, hollow out the interior
into a snug living-room. Our field-mice make
warm nests of grass, etc., in hollows of the soil
for winter residence; and one of them, the
jumping-mouse, weaves a ball of such materials,
placed in a bush, into which it creeps for hibernation.
Still more remarkable are the similar
but larger houses of the wood-rats (Neotoma),.
Thus Cram (‘American Animals,’ 1902) says
of the Alleghany wood-rat that it inhabits rocky
ledges among loose piles of broken rocks, “Here
he gathers together a mass of sticks, shreds of
bark, leaves and other debris to form a nest,
building them sometimes into a more regular
dome-shaped structure.”