Pigeons are successful is evident to anyone who has seen the huge populations of feral birds (all descended from domesticated Rock doves) dwelling in the cities of Europe, Asia, and America. These pigeons have benefited from the decline of their predators. The birds of prey, the presence of suitable nest sites on buildings, and the human habit of feeding them. Pigeons, being mainly seed-eaters, have also benefited from the spread of agriculture. In both cities and countries, this success has brought them into conflict with people.
The family is found almost worldwide, with members in all regions except Antarctica. Some species, such as the Rock dove and Collared dove are even found north of the Arctic Circle. Pigeons are good dispersers, judging from their wide distribution on islands of the India and South. Pacific Oceans, although they failed to reach a few isolated groups, such as the Hawaiian archipelago. Throughout their range. Pigeons occur in a wide variety of terrestrial habit-tats, from tropical rain forests to deserts, and from above the snowline in the Himalayas to the centers of the largest cities.
Pigeons generally have plump stocky bodies with a small head and bill and short legs. The plumage is soft and dense, and some tropical species are brilliantly colored or have ornamental crests, but most pigeons are dressed in neutral browns, grays, and pinks, although often with small bright, or iridescent, patches on the wings or neck.
In most species, the sexes look similar, with the female slightly duller, but in some, for example, the Orange dove, the sexes are very dif-ferment in color. Juvenile plumage generally differs from that of adults, but molt into adult plumage occurs within months of leaving the nest.
Pigeons are typically tree-dwelling, but some cliff-dwelling and ground-dwelling species occur too. Tropical fruit pigeons spend the most time in trees, feeding, roost-in, and nesting there, whereas many other species nest in trees but feed on the ground.
Pigeons and doves feed on a wide variety of vegetable matter, with seeds, fruits, leaves, buds, and flowers forming most of the diet, but many species take a limited amount of small snails and other invertebrates, par-secularly during the breeding season.
Most species have a strong muscular gizzard Anda a long narrow intestine. Grit is often taken to help break down hard seeds in the gizzard. Some fruit-eating species, such as the imperial pigeons, have strong stomachs and short wide guts. They digest only the pulp of the fruit they eat, voiding the stones Intact. Because the seeds are undamaged, pigeons can be important in the dispersal of fruiting plants, and many examples of the evolution of fruiting plants and pigeons are known.
Unlike most birds, pigeons drink actively by immersing their bill in water up to their nostrils and sucking without raising their heads. Some species may fly considerable distances to water, where they gather enlarge flocks at dawn and dusk.
As a family, pigeons have a very limited range of vocalizations, most of which are recognizable as modifications of a “cooing “call. Some species additionally utter muted cries in certain circumstances. Normal flights are often noisy and in some situations, this may be used as a social signal; during dies-play and escape flights a wide range of species apparently attract attention by the loud noise made by clapping their wings together.
Pigeons are strong fliers and some migrate thousands of kilometers, for example, the Turtle dove. Wing muscles make up as much as 32 percent of the body weight of Rock doves which have been specially bred for their speed and homing abilities. Good “racing pigeons” can achieve mean flight speeds of around 70km/h (44mph).
Pigeons are often gregarious, gathering enlarged flocks at good feeding or roosting sites. And some species, such as the Eared dove. Even breed colonially. The extinct Passenger pigeon of North America nested in enormous colonies: in the late 18th century there were thought to be as many as 3.000 million of them.
Some of the colonies occupied several square kilometers and it was so easy to shoot them in large numbers that the bird was hunted commercially even when it was greatly reduced in nun::The species was exterminated in about 1900 and the last specimen was Cincinnati Zoo in 1914.
Most pigeons and doves build a good-looking nest of interwoven twigs. The branches of a tree, but some man-made structures. Some species open situations on the ground, borsch as the Rock dove’s natural crevices or caves, and, exceptionally species such as the Stock dove nest hole in a tree or in a burrow.
Pigeons are very unusual among birds in that they produce milk which has a chemical composition similar to that produced by mammals: flamingos are the only other birds to share this feature. Pigeon or crop milk is a secretion of the adult crop which forms the complete diet of nestlings for the first few days of life. Thereafter. Nestlings are fed an increasing percentage of food items obtained by the parents, but the actual quantity of milk in the mixture remains fairly constant until the young are well-grown.
Crop milk is produced by both sexes in response to the secretion of the pituitary hormone, prolactin (the same hormone responsible for milk production in mammals). Prom about the midpoint of incubation the tissue of part of the crop begins to thicken and blood vessels grow into this region. Growth of the crop wall can more than triple the weight of the crop over the last half of incubation. And so by the time the young hatch, reddish folds with a honeycomb texture are visible in the crop. From this region, cells containing the “milk” are successively detached into the crop, and these are then regurgitated to the young. Milk cells are initially sloughed off only when the crop is empty, thus ensuring that it’s not contaminated by other foods. Later, crop milk production is confined to periods when adults tend the young, but the milk is mixed with other foods.
Crop milk is a thick solution (19-35 percent dry matter) with the consistency and appearance of cottage cheese. It contains 6 5-8 I percent water, and 13-19 percent protein.7-13 percent fat, 1-2 percent mineral matter, and vitamins A, B, and B2, but no carbohydrates. The dry matter is mostly protein, which is composed of a large variety of amino acids. Crop milk compares well with mammalian milk as a source of essential fatty acids: it is low in calcium and phosphorus but is high in sodium. Because of the high-water content, milk production puts a
relatively heavy drain on the adult body water reserves.
Milk production seems to be an adaptation to ensure that nestlings receive the adequate id predictable supply of energy and nutrients that are required for the high growth rates that are characteristic of pigeons.