Pigeons and doves

                             
Pigeons and doves constitute the bird clade Columbidae, that includes some 310 species. They are stout-bodied birds with short necks, and have short, slender bills with fleshy ceres. Doves feed on seeds, fruits, and plants. This family occurs worldwide, but the greatest variety is in the Indomalaya and Australasia ecozones.
In general, the terms "dove" and "pigeon" are used somewhat interchangeably. In ornithological practice, "dove" tends to be used for smaller species and "pigeon" for larger ones, but this is in no way consistently applied, and historically, the common names for these birds involve a great deal of variation between the terms. The species most commonly referred to as "pigeon" is the Feral Rock Pigeon, common in many cities.


                           

Doves and pigeons build relatively flimsy nests from sticks and other debris, which may be placed in trees, on ledges, or on the ground, depending on species. They lay one or two eggs, and both parents care for the young, which leave the nest after seven to 28 days.Unlike most birds, both sexes of doves and pigeons produce "crop milk" to feed to their young, secreted by a sloughing of fluid-filled cells from the lining of the crop. Young doves and pigeons are called "squabs".  (Wikipedia)


Class: Aves
Order: Columbiformes
Family: Columbidae

Description
Small to medium-sized birds; they generally have small heads and full-breasted bodies, and soft but very dense plumage

Size
5.9–31.5 in (15–120 cm); 1.1–4.4 lb (0.5–2 kg) Number of genera, species 42 genera; 316 species





Habitat
All terrestrial habitats, from desert to rainforest, and mangrove to high alpine mountains

Conservation status
Extinct: 11 species; Endangered: 14 species; Critically Endangered: 12 species; Vulnerable: 34 species; Near Threatened: 34 species

Distribution

Cosmopolitan, except the Arctic and Antarctica.

Physical characteristics
Pigeons have compact bodies and rather small heads on short necks. In most species the external sexual dimorphism is poorly developed. The wings are long and broad in many species, and consists of 10 primaries with the first reduced and 10–15 secondaries.



 Flight muscles are about 40% of total body mass; in poor fliers this is 14%. Columbid tails are usually long and broad, but some species have long, pointed tails. Twelve to 14 feathers build the tail. Crowned pigeons have 16–18 tail feathers. Pigeons lack down tracts, but all body feathers exhibit downy barbs at the base. Many pigeons have no oil gland at all, others have a small and naked oil gland. Preen oil is not used during preening. Powder-downs replace the function of preen oil.



The legs of arboreal pigeons are shorter than those of terrestrial pigeons. Tarsi (legs) are covered in front by large scales but laterally and behind with small ones; in Staroenas and Goura, front scales are also small. Feet are the perching type, with three toes in front and a large hind toe. Pigeons have short bills. The basal portion is swollen and covered with soft skin, the cere. The middle portion of the bill is constricted, giving it a plover-like appearance. Eyes are surrounded by bare skin that varies in color and may be red,
blue, yellow, or white. Two large lobes form the crop, which plays an important role in nutrition, when feeding young, and in vocalization. Caeca—cul-de-sac-like structures at the lower end of the gastrointestinal tract—are rudimental. The gall bladder is missing in most species.



Distribution
Fossil remains of some pigeons have been found from the Miocene in Europe, the Pliocene in North America, and the Ice Age in many parts of the world. Asia, especially southeast Asia, is considered a center of radiation for pigeons; the many archipelagos and most islands are inhabited by pigeons. Here we find more than half the total number of genera. The Americas follow with three monotypic genera, three genera containing less than five species, and five polytypic genera. Africa and Australia are inhabited by 10 genera each; two of these are monotypic genera. The New Zealand pigeon belongs to the monotypic genus Hemiphaga. A strong power of flight lets pigeons colonize distant ocean islands. Most islands of the Pacific Ocean, Polynesia, and Melanesia are inhabited by pigeons, often by several species on one island. The wood pigeon colonized the Azores, 780 mi (1,260 km) from the next inhabited place, and formed asubspecies. Forerunners of the Galápagos dove also had to cross more than 560 mi (900 km) of ocean to reach the Galápagos archipelago.

Habitat
There is considerable ecological differentiation. Most species are arboreal, with a few exceptions concerning the terrestrial forms of humid tropics and species bound to rock cliffs. True arboreal forms are the specialized pure fruit-eating fruit doves living in tropical rainforests. The savannas of America, Africa, and Australia are occupied by preferentially tree-bound species. Some species breed in colonies in the mangroves of the Caribbean, Australia, and Malaysia. There is considerable ecological differentiation. 



Most species are arboreal, with a few exceptions concerning the terrestrial forms of humid tropics and species bound to rock cliffs. True arboreal forms are the specialized pure fruit-eating fruit doves living in tropical rainforests. The savannas of America, Africa, and Australia are occupied by preferentially
tree-bound species. Some species breed in colonies in the mangroves of the Caribbean, Australia, and Malaysia.Cliff-nesting species occur mostly in Eurasia, but also in the Andes. The snow pigeon (Columba leuconota) is a close relative of the rock pigeon, which inhabits the high mountains of Asia from Afghanistan to western China, and often breeds in colonies nesting in cliff recesses and crevices. During summer the species inhabits great mountain heights, and in winter feeds at lower altitudes. Ernst Schäfer reports, “These large pigeons (0.6 lb; 280 g) never sleep at lower altitudes. In the evening they form great flocks and by the thousands, in groups of 100–200, fly up the valley cliffs to reach their sleeping quarters 15,100–16,400 ft (4,600–5,000 m) high, and some 6,600 ft (2,000 m) above the feeding grounds. As soon as the sun appears in the morning the same spectacle can be observed, only reversed. 



The pigeons always maintain the same flyway, and fly rapidly down into the valleys in great masses to feed to their satisfaction and return to the rough heights for night.




In California deserts the American mourning dove may breed at air temperatures to 111°F (44° C); in Australian deserts the common bronzewing (Phaps chalcoptera) lives in dry, hot conditions. Australian spinifex pigeons also live in a very hot habitat; they forage in morning shade and rest hidden in crevices during the hottest time of day. This species has a lower basal metabolic rate and a high upper critical temperature. At 113°F (45°C), ambient temperature gular (an area directly under the bill) fluttering starts. Otherwise, heat is dissipated through the skin by evaporative water loss.

Behavior
Many species show social behavior; we distinguish flocks, colonies, and aggregations. The flock is a small unit often formed for evident functional purposes such as foraging, commuting, roosting, or predator avoidance. The colony is a larger social unit characterized by spatial cohesion in connection with nesting or winter roosting behavior. The aggregation is a large social unit often composed of several flocks. An environmental feature such as a rich food source may cause an aggregation to form. Feral pigeons, for example, undertake foraging, flight, loafing, and roosting in flocks or aggregations of flocks. An individual pigeon in a flock may be safer from most forms of predation. Flocks provide the advantage of extra eyes for spotting predators and offering escape tactics, especially relative to high-speed predators such as falcons. Stable social hierarchies are demonstrated in roosting and feeding flocks.



 Birds observed in the center of a feeding group obtained more food. Those birds had heavier
weights than peripheral, subordinate individuals. Intraspecific aggression occurs over nesting territories, nesting places, or roosting perches. The aggressor pecks at the head and especially against the orbital skin, and strong wing beats occur; seldom are fights over food. Pigeons drink by immersing the bill and sucking—a most unusual method in birds. Only sandgrouse, buttonquails,
mousebirds, and some finches drink this way. This behavior lets pigeons take water from the most meager sources. The gait of pigeons is peculiar because of bobbing head movements, so the head stays on the same level while the body moves. The post-breeding molt is a complete descendant one. Molt is very slow, sometimes taking up to 10 months, and is not suspended during breeding. In the domestic pigeon, the wing molt starts before breeding and is interrupted when the nestlings hatch; it ends in autumn and may be interrupted by winter. In the European turtledove, the post-breeding molt starts in July, but is interrupted by the onset of the migratory disposition (new feathers complete their growth and old feathers will not fall). Therefore, the wing will be complete during migration. The rest of the molt, especially that of the tail feathers, occurs in the winter quarter. Preening with the bill rearranges feather vanes and disposes of ectoparasites. Mites, ticks, flies, bugs, lice, and fleas can be found on pigeons. The birds may disperse down-powder over the feather. After the first filling of the crop with food, pigeons use food-digestion time for preening. Doves, in general, have songs that are used in three contexts, corresponding with territorial or sexual drives. The advertising or perch-coo, the nest-coo delivered at the nest or
potential nest site, and the bow-coo, when the male is displaying
to the female. The advertising role of coos may be demonstrated
in caged pairs of American mourning doves by counting coos of the males before and after the females are removed: a 10-fold increase in cooing has been noted in males bereft of their mates. Cooing rates dropped to previous levels if the females were returned and pair bond was restored. The sexual role of dove song has been demonstrated by playing tape-recorded coos to captive African collared doves: the ovaries of female doves grew at a faster rate when exposed to tape recordings than in females not exposed to playback. Females respond to conspecific sound alone, independent of visual stimuli produced by the live male. Although songs are generally associated with male doves, many female doves also sing. A male song may stimulate the female to produce nest calls, and it is her own song that stimulates gonadotrophic hormone production in the hypothalamus; the male coo thus sustains the female’s cooing, which in turn stimulates production of pituitary hormones that stimulate ovulation. Playback has also been used to demonstrate that juvenile American mourning doves may recognize the male parent by characteristics in his individual song: the male sings to nestlings during his nest visitations, and so enables his progeny to learn the characteristics of his voice.

Feeding ecology and diet
Frugivorous (fruit-eating) and granivorous (grain- and seed-eating) species show special adaptations of the digestive tract. In seasonal climates pigeons are forced to switch among different food types. The nutmeg or pied imperial pigeon picks nutmegs directly from trees. Delacour and Mayr note that the pigeons can ingest extremely large fruits with huge pits; pits are regurgitated after the pulp is worked off.



 Fruit doves feed on nutmegs as soon as the brownish shell has cracked open. The nut itself, often as large as the bird’s head, is taken out of the shell and swallowed completely. There is usually room for only one hard-pitted fruit in the stomach.The stomach wall rubs off the thin layer around the nut by the action of two antagonistic muscle pairs, and only this envelope is digested; the large pit passes out unharmed. Seeds are mostly pecked from the ground surface. Especially soft grass seeds are stripped off the stem. 



The Galápagos dove digs with its long decurved bill for very hard seeds in the soil. The persistence and eagerness in collecting seeds is remarkable. Gasow found in a crop of a wood pigeon 8,050 capsules and 6,479 seeds of stitchwort (Stellaria sp.), with 30 cherries, 72 fragments of clover leaves, and 10 scale insects. Leaves, grass stems, buds, and flowers are a substantial part of the diet of granivorous pigeons when seeds and mast are not in season. Small snails are often found in crops and stomachs, but it is not clear if this supplements the calcium demand or is eaten directly as animal food. Eberhard Curio published a figure of a Negros bleeding heart (Gallicolumba keayi) with grasshoppers in its bill. 



The atoll fruit dove (Ptilinopus coralensis) can live on treeless coral atolls of the Toamotu archipelago in the Pacific Ocean far east of Australia. The diet may be purely animal, consisting of insects and even small lizards. The Wonga pigeon (Leucosarcia melanoleuca) from Australia is unusual among pigeons. Invertebrates (Blattodea and worms) form an important part of the diet. It has been observed scratching in leaf-litter like a gallinaceous bird and investigating lyrebird Menura display mounds in search of small snails, insects, and their larvae. Domestic pigeons will lower their body temperature under
conditions of extreme hunger after reducing locomotion. They store a small remainder of food in the crop and digest it before they awake in the morning to use the digestive heat (special dynamic adaptation) to warm their bodies.

Conservation status
About a third of all species are threatened according to the IUCN. Most problems occur with inhabitants of small, distant oceanic islands, where small populations exist that are put at risk by destruction of natural forested habitat. An exception to this was the passenger pigeon (Ectopistes migratorius), which was found in North America from the great plains eastward to the Atlantic, and from southern Canada to northern Mississippi. It lived in forest and open lowland.



Owing to well-developed social tendencies, the species normally
congregated in large numbers all year, and stories from early North American settlers suggest that millions of these birds roamed the great eastern forests in spring, summer, and fall. They were well known for a southward migration in dense masses of billions of individuals. Dense breeding colonies in forests extended over miles (kilometers). Clutch of one egg. Breeding season in the wild extended from April to September, and in captivity beginning in February.



The cause of the rapid extinction of this species is a subject of contention. Some researchers believe passenger pigeons were relatively inefficient at reproduction, and persisted only by maintaining enormous flocks because their reproductive rate was so slow. The only seeming explanation for the passenger pigeon’s decline and fall is that more died each year than were produced. Major causes of mortality did not include men with guns and large appetites for squab and sport shooting.



In migration the birds made a great impression on watchers. The classic report of this spectacle is from famed American observer, John James Audubon: “I spotted a flock of passenger pigeons, and I realized that the number of pigeons in the flock was greater than I had ever seen before, and I decided to count them. I got off my horse, sat down and began to pencil a dot on a piece of paper for each bird that I saw. Soon I discovered that it was impossible to continue, for the birds were coming in huge groups. In 21 minutes I had made 163 dots. 



As I departed, the flocks grew still denser, and the air was literally filled with pigeons; they darkened the sun as
in an eclipse, and their droppings fell like snowflakes. The whistling of their beating wings could practically make one fall asleep. During the entire time I waited for my lunch in Young’s Inn, and I saw legion after legion fly by; the width of the group measured from Ohio to the forested areas as far away as one could see.”
 Audubon tried to estimate the number of pigeons that flew by and came up with an astronomical figure: 1.1 billion birds. Passenger pigeons flew together, fed together, and roosted together. They were subject to shooting and other forms of collecting especially at roosts, and it is as much a result of this inordinate tendency to flock as anything else that they were so easy to kill.



Decline in numbers was noted in the late 1700s and considered marked by 1850. Probably to this point the decline represented the pigeons’ response to cutting forests. The well-documented great slaughters occurred only after the railroad had pushed into the central part of the continent, making it possible to ship birds reasonably rapidly to the great consumer markets of the east. Millions of adults and young were taken in the 1860s and 1870s, and hundreds of thousands in the early 1880s, but by the mid-1880s the species was showing that the end was near. Predictably, exploitation of nesting and roosting colonies continued into the 1890s, apparently being profitable at least to the small operator. The last wild passenger pigeon was killed in Ohio, in March 1900;
the last captive, a bird hatched in captivity named Martha that enjoyed great popularity, died in September 1914, at the Cincinnati Zoo. Pigeons as a game bird were hunted mostly by snare, by lime twigs, or by netting; eggs and nestlings also were collected. Pigeons as domesticated birds used for food, as pets, or for other purposes have played an important role in human history.

Significance to humans
Since ancient times pigeons have been domesticated and used as food and to transport messages.