The domestic pigeon (Columba livia "domestica" or Columba livia forma domestica) is a domesticated bird derived from the rock dove (Columba livia), of which it is also a subspecies. Although often termed a "subspecies", the domesticated pigeon does not constitute an accepted zoological subspecies of the rock dove, but a collection of over 350 breeds. The rock dove is among the world's first birds to be domesticated; Mesopotamian cuneiform tablets mention the domestication of pigeons more than 5,000 years ago, as do Egyptian hieroglyphs.
Pigeons have held historical importance to humans as food, pets, symbolic animals, and messengers. Due to their homing ability, pigeons have been used to deliver messages, including war pigeons during the two world wars. City pigeons, which are feral birds, are generally seen as pests, mainly due to their droppings and a reputation for spreading disease.
History of domestication
Which subspecies of C. livia was the progenitor of domestics, exactly when, how many times, where and how they were domesticated, and how they spread, remains poorly known; despite the long history of pigeons, little is known about the specifics of their initial domestication. Genetically, domesticated pigeons are closest to a cluster of origins of rock dove in the Middle East, particularly in the Syria – Jordan – Iraq – Arabian Peninsula region but also eastern Sudan, thus encompassing all or parts of the ranges of C. l. gaddi, C. l. palaestinae, and C. l. butleri.
Their fragile bones and similarity to wild birds make the fossil record a poor tool for their study. Thus most of what is known comes from written accounts, which almost certainly do not cover the first stages of domestication.
Pigeons were most likely domesticated at least 2000–5000 years ago, and may have been domesticated earlier as a food source. Some research suggests that domestication occurred as early as 10,000 years ago. The earliest recorded mention of pigeons comes from Mesopotamia some 5,000 years ago. Pigeon Valley in Cappadocia has rock formations that were carved into ancient dovecotes. Ancient Egyptians kept them. Akbar the Great traveled with a coterie of thousands of pigeons.
Because domestic and feral pigeons have extensively interbred with wild rock doves, genetically pure wild-type rock doves are now rare and endangered, confined to remote regions such as the oceanic fringes of the species' natural range, in particular the Outer Hebrides off western Scotland. This frequent admixture further muddies the true origins of pigeons.
The domestic pigeon was brought to the Americas by European colonists as an easy source of food and as messengers. Some sources state the species was first introduced to North America in 1606 at Port Royal, Nova Scotia, although other sources cite Plymouth and Jamestown settlements in the early 17th century as the first place for species introduction in North America.
Around the 18th century, European interest in fancy pigeons began, and breeders there greatly expanded the variety of pigeons, importing birds from the Middle East and South Asia and mixing different breeds to create new ones. Among these European fanciers was Charles Darwin, who was famously requested to write a book on pigeons during the process of writing On the Origin of Species. His own experiences with pigeon fancying would ultimately lead to another book; The Variation of Animals and Plants Under Domestication.
Genetics
From a genetic perspective, there are two loose ancestral clades of pigeons, but there is striking genetic homogeneity due to frequent interbreeding and human directed cross-breeding; pigeon fanciers often do not enforce breed standards, unlike with dogs. The first ancestral clade contains pigeons with exaggerated crops, tails, and manes; the second contains tumblers (the most diverse group), homing pigeons, owl pigeons, and those with exaggerated wattles. Over the millennia of human interaction with pigeons, a multitude of pigeon breeds have been created, which differ in either plumage or body structure.
Some varieties of domestic pigeon have modified feathers called "fat quills". These feathers contain yellow, oil-like fat that derives from the same cells as powder down. This is used while preening and helps reduce bacterial degradation of feathers by feather bacilli.
Markings A "wild-type" pigeon is closest in markings to the rock dove, which possesses a grading, slate-grey head and body with a green-purple iridescent neck, and ash-grey wings and tail with dark, often black, barring. They also differ structurally, with a thicker bill, a larger cere at the base of the bill compared to wild birds, a more flattened (less rounded) head profile, and a paler eye-ring. Due to millennia of selective breeding, including crossing with other Columba species, domestic pigeons possess major variations in plumage; often two birds from the same clutch may be of different colour. The domestic pigeon possesses 3 main colours; the wild-type blue, brown, and ash-red. This variation in colour is linked to the parent's sex chromosomes; as animals with the ZW chromosome system, cockbirds possess the colour genes from both parents, while hens only inherit their father's colour and patterns. Additionally, there is some dominance observed; ash-red is dominant over the other two base colours, while blue is dominant over brown. Recessive red is a unique colour which is inherited differently from the three base ones; it is distinct from ash-red in that the bird always is a uniform chestnut colour.
Another important aspect of pigeon markings is the pattern on the wing coverts, which exists in four variants; wild-type bar, check, T-check, and barless. T-check is the most dominant pattern, followed by check, barred, and the least dominant barless pattern. Additionally, the modifiers spread and dilute affects the expression of the colour; the spread gene spreads the colour of the bird's tail to its entire body, while dilute lightens the bird's overall colour, as if were a dye being diluted to reduce its saturation.
There are many other markings present in pigeons; among them are milky, almond, opal, dirty, indigo, grizzle, and various "stencil" and "bronzing" factors; all of which further modify the base markings of a bird. Conversely, pigeons possess multiple genetic pathways that can produce a completely white bird.
Crest A recessive allele in the EphB2 gene controls the crested-feather mutation in domestic pigeons. Pigeons with two copies of the crest allele grow neck and head feathers that point towards the top of the head, unlike other feathers that point towards the tail. Additionally, bacterial growth analysis suggests that crested pigeons have reduced bacterial-killing abilities due to reduced kinase activity. Pigeons may express the crest gene differently depending on its genetic heritage; two squabs from the same brood descending from the same pair may have one bird develop a peak crest, and the other a wild-type smooth head.
Foot feathering
Pigeons with feathers growing on their feet have differently expressed genes: a hindlimb-development gene called PITX1 is less active than normal, and a forelimb-development gene called Tbx5 that normally develops the wings is also active in the feet, causing both feather growth and larger leg bones. The cause of these changes is a change in the regulatory sequences of DNA that control the expression of the Pitx1 and the Tbx5 genes, rather than mutations in the genes themselves. Pigeon foot feathering has been studied as a potential model for the transition from feathered to "scaled" feet in non-avian dinosaurs. It is thought that large feathers, especially flight feathers on the feet were lost in all living birds as it was too inefficient in powered flight. Domestic pigeons quickly overheated when flying with their scaled feet covered, and it is thought that the loss of microraptorian-like hind-wings allowed for more efficient powered flight.
Crop inflation Pouter- or cropper breeds exhibit the trait of inflating their crops with air, producing their signature "globe". This trait is inheritable and partially dominant, though cockbirds tend to exhibit this trait more than females. Some cropper breeds may have issues with passing food and water through their crops, though this problem isn't universal and can be treated by owners.
Hybridisation There is strong evidence that some divergences in appearance between the wild-type rock dove and domestic pigeons, such as checkered wing patterns and red/brown colour, may be due to introgression by cross-breeding with the speckled pigeon C. guinea. However, there is little evidence of this in their genetic structure, with C. guinea instead being sister to the common wood pigeon C. palumbus.
Domestic pigeons may be crossed with the barbary dove (Streptopelia risoria) to create offspring, but the offspring are not fertile.
Life history
Reproduction
Domestic pigeons reproduce exactly as wild rock doves do; settling in a safe, cool nook, building a flimsy stick nest, and laying two eggs that are incubated for a little longer than two weeks, usually 17 to 19 days. A pigeon keeper may select breeding partners, but in an open loft the birds choose their own mate. Both sexes of pigeons are extremely protective of their eggs and young, and often defend them vigorously from nest predators, including their human keepers; they are defensive of their personal space, and see their nests as extensions of said space.
Baby pigeons are called squabs, squeakers, or peepers, the latter two being a reference to their cry when begging for food. Initially, the squabs are fed by their parents with crop milk, which contains high amounts of protein and fat, some breeds are bred into such debilitating forms that they may require human intervention to produce squabs successfully, which necessitates the owner to raise them themselves by feeding the chicks with special squab formula (similar to infant formula) or by fostering them under another pair of pigeons. This may also be necessary if the parents are unable or unwilling to raise the squab. When fed by their parents, the squabs develop much faster than other species of poultry, such as quail, and fostering in human care may be more effective than using a surrogate pair of pigeons.
As the chicks grow and become more mobile and alert, their parents transition them to their adult food of seeds and grains. A pigeon hen may start a new clutch before her previous one has fledged, in which case her mate raises the previous clutch on his own. Pigeons reach their adult size around four weeks of age, and after fledging the chicks will follow their parents to the communal feeding ground; areas with plentiful forage that a pigeon flock uses. Here the chicks gain their independence and integrate into pigeon society.
Domestic pigeons were selected to breed faster than their wild ancestors; a lack of a breeding season, abundance of food in a domestic setting, and swift maturity (squabs fledge in about a month, and often have already bred and fledged a few clutches of their own before reaching a year in age) leads to swift population growth of pigeons in the flock. This fact, and the number of pigeons lost in races or intentionally released, leads to exponential growth in free-living, feral populations.
Life stages
Pigeon related illness
Pigeon breeders sometimes suffer from an ailment known as bird fancier's lung or pigeon lung. A form of hypersensitivity pneumonitis, pigeon lung is caused by the inhalation of the avian proteins found in feathers and dung. It can sometimes be combated by wearing a filtered mask.