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 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.
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.
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