Pigeons
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Subphylum:Vertebrata
Class:Aves
Order:Columbiformes
Family:Columbidae

Pigeons and doves constitute the family Columbidae within the order Columbiformes, which include some 300 species of near passerine birds. In general parlance the terms "dove" and "pigeon" are used somewhat interchangeably. In ornithological practice, there is a tendency for "dove" 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 term "dove" and "pigeon." This family occurs worldwide, but the greatest variety is in the Indomalaya and Australasia ecozones. The young doves and pigeons are called "squabs."
Pigeons and doves are stout-bodied birds with short necks and short slender bills with a fleshy cere. The species commonly referred to just as the "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 7 to 28 days. Doves feed on seeds, fruit and plants. Unlike most other birds the doves and pigeons produce "crop milk," which is secreted by a sloughing of fluid-filled cells from the lining of the crop. Both the sexes produce this highly nutritious substance to feed to the young.

Biology

Morphology
Pigeons and doves exhibit considerable variations in size. The largest species are the crowned pigeons of New Guinea, which are nearly turkey-sized, at a weight of 2-4 kilograms (4.4-8.8 lbs.) The smallest are the New World ground-doves of the genus Columbina, which are the same size as a House Sparrow and weigh as little as 22 grams. With a total length of more than 50 centimeters (19 in) and weight of almost a kilo (2 lb), the largest arboreal species is the Marquesan Imperial-pigeon, while the Dwarf Fruit-dove, which may measure as little as 13 centimeters (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 there is no taxonomic basis for distinguishing between the two.
Overall, the Columbidae tend to have short bills and legs, small heads on large compact bodies. 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 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. 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.