NEST. Nidification or the practice of making nests concerns all that appertains to the preparation for the reception of eggs, or newly-born young, and the subsequent care thereof on emergence. Our conceptions of nidification are commonly derived from ob servations on birds; but mammals, reptiles, amphibia and fishes, as well as invertebrates, include species which make more or less elaborate preparation in advance for the reception of their young.
The first stage in this sequence commonly consists in the selec tion of a definite site whereon, with a few exceptions, a nest is built in, or on which the eggs, or young, are deposited. Two factors govern this preparation,—the conditions of the environment, and the state of the young on emergence.
Birds.—With the birds a nest is not invariably made, as for example with the guillemot whose single egg is deposited on a bare ledge of rock projecting from the face of a cliff rising steeply from the sea. Species which haunt sandy wastes make little or no prepa ration by way of a nest. This receptable seems originally to have been made for the purpose of keeping the incubating bird, and the eggs, from contact with cold, damp earth.
Much more elaborate are the nests of the smaller species. These placed in hedgerows, or bushes, or even on the ground, are bowl shaped structures made of fine grass-stems interwoven with horse-hair, and cunningly masked by moss or lichen, as in the case of the long-tailed titmouse. Some, like the thrush, use a foundation of clay, and line the interior of the nest with a mix ture of decayed wood and cow-dung. Some of the African weaver birds, and of the American hang-nests, suspend the nest, which is made of long grass-stems, and vegetable fibres, by a long "rope" attached to the bough of a tree. Towards the end this rope is en larged to form a spherical chamber, with an entrance at the side in the hang-nests; and at the end of a further extension of the rope beneath the nest in the weavers.
Some of the flower-peckers of Africa build a nest of felted cotton-down. A few species make a more or less extensive use of saliva as a cement for mud-built nests, as with the swallow-tribe, the oven-bird, and the flamingo. The use of salivary glands in
nest-building attains to its maximum with the edible swifts which use saliva alone. Such nests are used by the Chinese in making bird's nest soup.
Hollow trees are used by many birds, such as the parrots and the woodpeckers, the eggs being deposited on the rotten wood at the bottom of the hole. Others, like the sand-martin and the kingfisher drive long tunnels into the face of a sand-bank, enlarg ing the end of the tunnel to form a nest-chamber. The greatness of this achievement is commonly overlooked ; for it would be diffi cult to find birds more apparently unsuited for such a task, since the sand-martin has the feeblest of feet and an extremely short beak, while the short legs, and syndactyle toes of the kingfisher, coupled with its long, pointed beak, seem still less fitted for bur rowing.
While there is general conformity of type characteristic of the nests of the different groups of birds, there are striking excep tions to the rule. Thus the stork-tribe are content with a simple platform of sticks; but the hammer-head (Scopus umbretta) builds a huge nest of mud and sticks, covered in by a roof so substantial as to bear easily the weight of a man. This roof may be as much as 6f t. across. The flamingo, again, builds a steep pedestal of mud, the top of which is scooped out to receive the eggs. Parrots nest in hollow trees, but the quaker-parrot (Myop sittacus) of South America builds a large domed nest of sticks.
The Gallinaceous birds make little more than an apology for a nest, fashioned in a depression in the ground. But the mega podes of Celebes, New Guinea and Australia build a huge mound of decaying vegetable matter, and laying their eggs deep down in the fermenting mass leave them to hatch by the heat thus en gendered.
One of the most remarkable cases of nidification among birds is furnished by the horn-bills. The eggs are laid at the bottom of a cavity in a tree, and as soon as the female has started incuba tion, the entrance-hole is closed by the male by means of clay; but a space is left open wide enough for his mate to push her beak through to receive food.