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".
The Pteroclididae (sandgrouse) were formerly included in the order Columbiformes largely due to this drinking behavior ("The only other group, however, which shows the same behavior, the Pteroclididae, is placed near the doves just by this doubtlessly very old characteristic." ); more recently, it had been reported that they cannot drink by "sucking" or "pumping", and they are now treated separately in the order Pteroclidiformes and are considered to be closer to the shorebirds.
Columbidae are usually divided into five subfamilies, probably inaccurately. For example, the American ground and quail doves, which are usually placed in the Columbinae, seem to be two distinct subfamilies.[5] The order presented here follows Baptista et al. (1997) with some updates (Johnson & Clayton 2000, Johnson et al. 2001, Shapiro et al. 2002).
Osteology and DNA sequence analyses indicate the Dodo and Rodrigues Solitaire are better considered as a subfamily Raphinae in the Columbidae pending availability of further information.
The arrangement of genera and naming of subfamilies is in some cases provisional, because analysis of different DNA sequences yield results that differ, often radically, in the placement of certain (mainly Indo-Australian) genera. This ambiguity, probably caused by long branch attraction, seems to confirm the first pigeons evolved in the Australasian region, and that the "Treronidae" and allied forms (crowned and pheasant pigeons, for example) represent the earliest radiation of the group.
As the Dodo and Rodrigues Solitaire are in all likelihood part of the Indo-Australian radiation that produced the three small subfamilies mentioned above with the fruit-doves and -pigeons (including the Nicobar Pigeon), they are here included as a subfamily Raphinae, pending better material evidence of their exact relationships.
Exacerbating these issues, columbids are not well represented in the fossil record. No truly primitive forms have been found to date. The genus Gerandia has been described from Early Miocene deposits of France, but while it was long believed[citation needed] to be a pigeon, it is more likely a sandgrouse.[citation needed] Fragmentary remains of a probably "ptilinopine" Early Miocene pigeon were found in the Bannockburn Formation of New Zealand and described as Rupephaps; "Columbina" prattae from roughly contemporary deposits of Florida is nowadays tentatively separated in Arenicolumba, but its distinction from Columbina/Scardafella and related genera needs to be more firmly established (e.g. by cladistic analysis). Apart from that, all other fossils belong to extant genera. For these, and for the considerable number of more recently extinct prehistoric species, see the respective genus accounts.

Description
Pigeons and doves exhibit considerable variations in size. The largest species is the Crowned Pigeon of New Guinea, which is nearly turkey-sized, at a weight of 2–4 kg (4.4–8.8 lb) The smallest is the New World Ground-Dove of the genus Columbina, which is the same size as a House Sparrow and weighs as little as 22 g. With a total length of more than 50 cm (19 in) and weight of almost 1 kg (2 lb), the largest arboreal species is the Marquesan Imperial Pigeon, while the Dwarf Fruit Dove, which may measure as little as 13 cm (5.1 in), has a marginally smaller total length than any other species from this family. Smaller species tend to be known as doves, while larger species as pigeons, but no taxonomic basis distinguishes between the two.
Overall, the Columbidae tend to have short bills and legs, and small heads on large compact bodies. Their characteristic head bobbing was shown to be due to their natural desire to keep their vision constant in a 1978 experiment by B. J. Frost in which they were placed on treadmills – they did not bob their heads as their surroundings were constant. The wings are large and have low wing loadings; pigeons have strong wing muscles (wing muscles comprise 31–44% of their body weight) and are amongst the strongest fliers of all birds. They are also highly maneuverable in flight.


The Common Indian Dove mostly seen in the Villages of India
The plumage of the family is variable. Granivorous species tend to have dull plumage, with a few exceptions, whereas the frugivorous species have brightly coloured plumage.[8] The Ptilinopus fruit doves are some of the brightest coloured pigeons, with the three endemic species of Fiji and the Indian Ocean Alectroenas being amongst the brightest coloured. Pigeons and doves may be sexually monochromatic or dichromatic. In addition to bright colours, pigeons may sport crests or other ornamentation.
Like some other birds, Columbidae have no gall bladders. Some medieval naturalists concluded they have no bile (gall), which in the medieval theory of the four humours explained the allegedly sweet disposition of doves. In fact, however, they do have gall (as Aristotle already realised), which is secreted directly into the gut.