Nests.—The nests of birds (see NEST) exhibit a wide range in form and many have wonderful features.
The skimmer (Rynchops nigra) and the least tern (Sterna antil larum) excavate a slight hollow in sand or gravel to contain the eggs. The American avocet (Recurvirostra americana) may line a slight depression near the water's edge with a few bits of weed stem, and there deposit its four eggs. Subsequently, should the waters increase in freshet the avocet hustles about gathering grass, bits of wood, feathers, small bones and weeds to raise its treasures above the flood, so that where necessity arose, these birds have been known to erect piles of rubbish a foot in height. If the waters subsequently subside these elevated nests become con spicuous structures, but are not removed.
Some ground-nesting birds regularly conceal their eggs in holes. The Manx shearwater (Puffinus puffinus) digs burrows in loose soil, and makes its nest at the end of the tunnel. There may be variation in method in one species, however, as the wedge-tailed shearwater (Puffinus pacificus) of the Pacific islands ordinarily excavates a hole for nesting, but on rocky islands, where there is little soil, may deposit its egg on the ground, under bushes, or even in the open. The little auk or dovekie (Alle alle) searches out a crevice or shelter beneath boulders, often on talus slopes where rock fragments are piled in great confusion. The belted kingfisher (Streptoceryle alcyon) digs a tunnel on the face of a steep bank and lays its eggs at the end, gradually building up a mass of fish bones from regurgitated pellets for a nest.
Concealment is sought also by some tree-nesting birds. The scops owl (Otus scops) of Europe, and the screech owl (Otus asio) of North America, seek hollows in trees, where the eggs are placed without nest lining of any kind. Woodpeckers excavate special chambers in the trunks of trees, placing their eggs on • an accumulation of chips at the bottom. Though dead trunks are usually chosen, the yellow-bellied woodpecker (Sphyrapicus varius) frequently drills its home in a living hardwood tree, and the Porto Rican woodpecker (Melanerpes portoricensis) may nest in a living palm trunk.
Nests of many herons, e.g., the night-heron (Nycticorax nycti corax), are placed in trees, and are flat structures of twigs and sticks that form a mere platform, so loosely built that the eggs may often be seen from below. Among larger nests there is every variation from this type to that of the osprey (Pandion haliaetus) to which material may be added year after year until the mass is 8 or i o ft. in diameter and makes a cartload in bulk.
Among smaller birds, the tree nest is usually a simple cup that has a foundation of rough material on which the nest proper of finer material rests; the lining is made of soft substances, as root lets or plant downs. The blackbird (Turdus merula) and the American robin (Turdus migratorius) line their nests with cups of mud, within which are placed soft grasses. Many birds place
nests of grasses and rootlets under herbage or in thickets on the ground. For protection, many tree-nesting birds build homes with arched tops that wholly conceal the eggs. There is a great group of birds in South America, the so-called tracheophones, many of whose species have this habit. Conspicuous among them in the Argentine is the lefiatero, or firewood-gatherer (Anumbius an numbi), that gathers a quantity of thorny twigs to form a spherical mass, within which is placed the nest proper, reached by a runway, the whole so firmly constructed that the eggs inside may be reached only with difficulty. These nests are durable and last for several years, until the materials composing them decay. The oven-birds (Furnarius) in this group construct rounded masses of mud, with an entrance at one side, the walls being an inch or more in thickness, and so built that they will withstand the beating of heavy rains without damage.
Many of the troupial family (I cteridae) make purse-like nests that are suspended in the tops of trees. The nest of the oropen dola (Gymnostinops montezuma) of Central America may be 5 ft. in length, suspended by the upper end, below which is located the entrance which leads through a long, constricted neck to the expanded lower part, where the nest proper is placed. The oro pendola nests in colonies, but nests of the orioles, as the Baltimore oriole (Icterus galbula) which also constructs a purse-shaped nest from 8 to i o in. in length, are found alone. The nests of the social weaver-finches of southern Africa are among the most re markable structures known in the bird world. These birds are gre garious and, in company, accumulate masses of grass in trees to form a roof, under which each pair of birds has its separate cubicle, lined warmly with feathers. From 20 to 30o pairs may inhabit a single structure, which grows in size as it is inhabited year of ter year, until it may contain several wagon-loads of material.
Among other curious nests there may be mentioned those of the edible-nest swiftlets of the Indian, Australian, and South Pacific areas, that are cupped platforms, composed of a coagulated mucus secreted by the mouth-glands of the birds, placed on the walls of caves. These are gathered commercially and form the basis for a soup highly prized by the Chinese. The American chimney swift (Chaetura pelagica) makes a nest of twigs, cemented together by mucus from the mouth, to make a tiny basket. In early times these nests were placed on the inside of hollow tree-trunks, but with the advent of the Caucasian race and the building of houses, hollow trees have been forsaken for chimneys.
Nest-building with most birds seems to be usually the duty of the female. The male may assist by bringing material and may lay it on the nest, but it is mainly arranged by the female. In many species the entire work devolves upon the female.