Pigeons and doves constitute the bird family Columbidae within the order Columbiformes, which include some 300 species of near passerines. In general 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 terms "dove" and "pigeon." This family occurs worldwide, but the greatest variety is in the Indomalaya and Australasia ecozones. Young doves and pigeons are called "squabs."
Pigeons and doves are stout-bodied birds with short necks, and have short slender bills with a fleshy cere. The species commonly referred to just 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 7 to 28 days. Doves feed on seeds, fruit and plants. Unlike most other birds (but see flamingo), the doves and pigeons produce "crop milk", which is secreted by a sloughing of fluid-filled cells from the lining of the crop. Both sexes produce this highly nutritious substance to feed to the young.
Seeds and fruit form the major component of the diet of pigeons and doves. In fact, the family can be divided into the seed eating or granivorous species (subfamily Columbinae) and the fruit eating or frugivorous species (the other four subfamilies). The granivorous typically feed on seed found on the ground, whereas the species that feed on fruit and mast tend to feed in trees. There are morphological adaptations that can be used to distinguish between the two groups, granivorous species tend to have thick walls in the gizzards, whereas the frugivores tend to have thin walls. In addition fruit eating species have short intestines whereas those that eat seeds have longer ones. Frugivores are capable of clinging to branches and even hang upside down to reach fruit.
In addition to fruit and seeds a number of other food items are taken by many species. Some species, particularly the ground-doves and quail-doves take a large number of prey items such as insects and worms. One species, the Atoll Fruit Dove is specialised in taking insect and reptile prey. Snails, moths and other insects are taken by White-crowned Pigeons, Orange Doves and Ruddy Ground Doves.