Plumage and Coloring

The bird's feathers have many purposes. They streamline the body, aiding the bird to move swiftly through the air or water. They protect it from heat or cold. Stiff, strong wing and tail feathers are essential for flight.

In some species, the feathers of the male are brightly colored to attract a mate. Less often, the female has the bright feathers. Many birds are patterned to harmonize with their surrounding so that they will be less conspicuous to their enemies. This protective coloration is especially useful during the nesting season when the parent birds do not wish to attract attention to their nests. Most young birds are protectively colored.

Many birds are brilliantly colored, but many others have dull plumage. The peafowl is among the most colorful of birds. The golden pheasant of Asia is nearly as brilliant. The greater bird of paradise found in New Guinea has elongated flank feathers that form ornamental plumes. Colorful birds of North America include the flamingo, scarlet tanager, Baltimore oriole, bluebird, cardinal, goldfinch, and wood duck.

Molting is the periodic shedding of feathers and the growth of new ones. All birds molt at least once each year. The most complete molt comes after breeding. Some birds have partial molts in spring to take on more brilliant colors for the breeding season. Usually the wing feathers molt a few at a time, so that the bird's flying ability is not seriously harmed. Male ducks and geese, however, shed all flight feathers at once and are unable to fly. Birds are quiet and keep to themselves during molting time, but are not particularly weak or helpless.

Some birds, such as hawks and owls, keep the same mate for life. Most birds, however, choose a new mate each year, and carry on an active and sometimes competitive courtship. Courtship functions not only in selecting a mate but also in driving away competitors, stimulating ovulation in the female, and helping members of a species to recognize each other. A male bird usually selects the nesting site and defends his territory from intruders. He attempts to attract a female with calls and songs, physical contact such as sparring with his bill, displays of bright feathers, elaborate dances, and morsels of food.

Some courtships are very elaborate. The male prairie chicken inflates large yellow air sacs on either side of his head, making a loud booming sound. As he gives this serenade, he performs a dance to attract a female.

The bowerbird of New Guinea builds an enclosure, or bower, decorated with leaves, flowers, and other materials. The male displays his feathers and dances near the bower to win the watching female.

Most birds build some type of nest to protect the eggs and the young from harsh weather and from predators. Nests also retain heat, which promotes incubation of the eggs. Each species uses a distinctive set of nesting materials.

Some seabirds, such as the auk and guillemot, lay their eggs on a rock or the edge of a cliff without building a nest. Others, such as gulls and terns, collect piles of seaweed or grass. Grebes, coots, and rails make floating nests of reeds and rushes. Ducks, geese, and swans seek dry spots hidden among rushes or undergrowth, and build substantial nests lined with down from their own breasts. The nest of the eider duck is a source of down, which has commercial value as stuffing for pillows, quilts, and comforters and for lining winter coats.

Many wading birds, such as herons and most storks, nest in colonies, building platforms of sticks high in the trees. The colony rarely exceeds a dozen nests. Penguins, terns, and gulls, on the other hand, often nest in colonies of 100 to 1,000 nests. They use stones as nesting material.

Most birds of prey build bulky nests in high trees or on mountain ledges. Owls usually prefer hollow trees, abandoned buildings, or the old nest of another bird. The elf owl of the southwestern United States makes its nest in a hollow cactus.

Woodpeckers, sapsuckers, and flickers cut holes for their nests in dead trees or old utility poles. The chimney swift builds a bracketlike nest of twigs and gluey saliva halfway down the inside of an unused chimney. The hummingbird builds its nest of spider webs. Certain Asiatic swifts make their nests almost entirely out of saliva, which then hardens; it is this nest that is used by the Chinese to make bird's-nest soup.

Songbirds build many kinds of nests. The robin builds a cup-shaped nest on a tree limb. The outside is composed of coarse grasses and leaves; the inside is plastered with mud and lined with fine grasses. The Baltimore oriole weaves a hanging pouch of grass, hair, strings, and roots. The grosbeak, crossbill, goldfinch, indigo bunting, and cardinal build hemispherical nests in bushes or trees, from 5 to 30 feet (1.5-9 m) above the ground.

The tailorbird sews the edges of growing leaves together with grass. At nesting time, the male hornbill seals the female and her eggs in a hollow tree by building a wall of dried mud, leaving only a small opening for air. He attends her during the hatching period, passing food through the opening. When the young are fledged (acquire feathers), the mother breaks down the wall. The brush turkey of Australia builds a mound-shaped nest of refuse, earth, and decaying vegetation. The eggs are hatched by the heat generated by the decay process.

The American cowbird and the European cuckoo do not make nests of their own. Instead, they lay eggs secretly in the nest of another bird. The eggs are hatched and raised by unsuspecting foster parents, and often the rightful young are crowded out of the nest by the larger baby cowbirds or cuckoos. Some birds build a new nest on top of one that is found to have cowbird or cuckoo eggs in it.

Birds lay one to as many as 23 eggs. Most eggs are oval but some species produce elongated or spherical eggs. Eggs of the auk and guillemot are pointed at one end and broad at the other; they roll in a circle if disturbed, preventing them from rolling off the edge of the cliff where the eggs are laid.

Most eggs have a smooth texture but some are pitted or corrugated. The eggs of ground-nesting birds have blotches, specks, and streaks that camouflage them. Eggs range in color from white to brown, green, and light blue.

Eggs must be incubated, or warmed, for 11 days to eight weeks before they will hatch. In most species the eggs are incubated by the parents, who warm the eggs by sitting on them. This may be the job of the female, of the male, or of both parents. Parents who incubate the eggs develop a brood patch, an area of bare skin on the belly. The feathers in this area fall out and the dermis of the skin becomes richly supplied with blood vessels; heat from the blood vessels is transferred from the warm brood patch to the eggs. Some birds, such as boobies and gannets, stand on the eggs, warming them with their webbed feet. Emperor penguins warm the eggs by placing them on top of their feet, where they are covered by a special fold of skin on the underside of the belly. In other species, eggs are incubated indirectly by the heat of the sun or of decaying vegetation.

While still in the shell the young, or chick, develops an egg tooth, a short, pointed horny structure at the tip of the upper mandible. It helps the chick peck its way out of the shell.

The egg tooth drops off or is worn away within 40 days after hatching.

Chicks of different species are born at different levels of maturity. They are either precocial or altricial. Precocial chicks are born covered with down and with their eyes open. They mature very rapidly. Altricial chicks, on the other hand, are born virtually helpless. They are naked at birth, blind, and too weak to stand. They usually remain in the nest for days or weeks.

One or both of the adult birds hunt food for the young, keep them warm at night, shelter them from the weather, and protect them from predators. In some species, the parents teach their young to fly or swim; in others, the young learn for themselves.