Pigeons and Doves
Pigeons and Doves
Pigeons and doves include about 316 species of birds in the family Columbidae. Most species are found in forests of various types, with fewer species occurring in more open habitats. By far the greatest richness of species of pigeons and doves occurs in moist tropical and subtropical forests. Many tropical oceanic islands have endemic species of pigeons and doves that evolved in isolation. Many of these local (or endemic) species have become endangered by habitat loss or predation by introduced mammals (such as cats and rats), and some are already extinct.
Larger birds in this family are usually called pigeons, while the smaller ones are called doves. Other than this vague criterion, there is no substantial difference between pigeons and doves.
Birds in this family are distinguished by their relatively small head, short neck, a soft but dense plumage, and a naked, fleshy tissue (known as a cere) at the top of the upper mandible. Pigeons typically have “cooing” calls, which are used in courtship and in some respects are equivalent to the songs of other birds. The plumage of many species of pigeons is a subdued gray, brown, and white, and is often tinged with iridescence. However, some tropical species have very bright and spectacularly colored plumage.
Biology of pigeons and doves
The smallest species of pigeon is the diamond dove (Geopelia cuneata ), only 2 in (15 cm) long and weighing 1 oz (30 g). The largest species is the Victoria crowned pigeon (Goura victoria ), 32 in (80 cm) long and 5 lb (2.4 kg) in weight.
Most pigeons are strong fliers, and some species are capable of undertaking long-distance movements and migrations. Other pigeons, especially those living in moist tropical forest, are local birds that spend a
great deal of time walking on the ground, foraging for their food of fruits. The pheasant pigeon (Otidiphaps nobilis ) of New Guinea is almost entirely terrestrial, and rather fowl-like in its appearance and behavior.
Pigeons are almost entirely seed and fruit eaters. Pigeons have a large, muscular gizzard, which is useful in grinding hard fruits, for example tree “mast” such as acorns, hazelnuts, chestnuts, and other nutritious fruits that most birds are not capable of digesting.
Pigeons have the ability to suck water when drinking. This is rather distinctive, because almost all other birds can only swallow water by taking some into their mouth, and then tilting their head back to let the liquid run down their throat.
Pigeons are monogamous, laying one to two eggs on a rough platform nest, commonly built of twigs. Both sexes share the incubation of the eggs, the male during the day, and the female at night. Young pigeons are initially fed with a material known as “pigeon milk,” which is a rich, nutritious secretion of the lining of the crop of the adult birds. This material is collected from the crop by the young birds, which must insert their head rather deeply into the adult’s throat to do so. Older chicks are also fed regurgitated seeds and other plant foods.
Pigeons of North America
Seven native species of pigeons occur regularly in North America. The most widespread of these is the mourning dove (Zenaidura macroura ), named after its loud, soulful cooings. This species occurs widely south of the boreal forest. The mourning dove is migratory in the northern parts of its range, although suburban birds can manage to survive the winter if they have access to dependable food at feeders.
All other native pigeons are relatively southern in their distribution. The band-tailed pigeon (Columba fasciata ) and white-winged dove (Zenaida asiatica ) are southwestern in distribution, while the ground dove (Columbigallina passerina ) also occurs in the Southeast. The white-crowned pigeon (Columba leucocephala ) only occurs in the Florida Keys and a few places on the immediately adjacent mainland.
Wherever these native pigeons are abundant, they may be hunted for sport. One North American species, the passenger pigeon (Ectopistes migratorius ), was driven into extinction as a result of overhunting for sale in urban markets.
The domestic pigeon
The natural range of the rock dove or feral pigeon (Columba livia ) was probably regions of the Mediterranean basin with rocky cliffs where these birds can nest. However, this species has been domesticated by humans, and it has now been introduced to suitable habitats around the world, including North America. The rock dove may now be the world’s most widely distributed bird.
The domestic pigeon is the cultivated variety of Columba livia that is raised for food. It is most commonly the young birds, which are known as squabs, that are eaten.
The domestic pigeon develops an intense affinity for the place where it nests and roosts at night. This bird is also very skillful at finding its way back to its home roost after it has been taken some distance away. Humans have exploited this characteristic by using “carrier pigeons” to transport messages over long distances. The invention of the radio and other methods of long-distance communication eventually replaced carrier pigeons, but competitions are still held to test the homing abilities of individual racing birds. Scientists have long debated the basis of the pigeon’s homing ability, with some attributing it to magnetic navigation and others to sense of smell. Recent research seems to confirm that pigeons primarily use their senses of smell to find their way home.
Domestic pigeons have also been bred into some very unusual varieties of color, feather displays, and body shape. People who find the aesthetics of unusual pigeons to be interesting form clubs, and they avidly compare, trade, and sell their varieties of domestic pigeons.
Feral pigeons are domestic pigeons that have escaped and are breeding in the wild. Feral pigeons usually live in cities and other built-up areas, although they sometimes breed in more natural habitats as well. These birds are often considered to be pests, because they can be a nuisance when abundant, soiling statues and buildings with their excrement, and sometimes fouling people walking along streets or in parks.
However, feral pigeons are among the few non-human creatures that can tolerate the environmental conditions of cities, and they contribute a positive aesthetic to urban areas. Many people enjoy hand-feeding urban pigeons in parks and other public places where these birds can be abundant and tame.
A few other species of pigeons are kept in captivity, usually as pets. Common ornamental pigeons include the collared dove (Streptopelia decaocto ), spotted dove (S. chinensis ), turtle dove (S. turtur ), and ringed turtle dove (S. risoria ). Some of these birds have escaped from captivity and established feral populations outside of their natural range, for example, in southern parts of the United States.
The passenger pigeon
One of the most famous examples of an extinction caused by humans involves the passenger pigeon. This species became extinct in the early twentieth century through gross overhunting coupled with the loss of most of its natural habitat of mature angiosperm forests, which was widely converted to agriculture.
The natural range of the passenger pigeon was southeastern North America. Prior to its overhunting, about 300 years ago, the passenger pigeon may have been the world’s most abundant land bird. Its pre-impact population has been estimated at three to five billion individuals, which may have accounted for one quarter of the population of all birds in North America.
During its migrations, the passenger pigeon formed tremendous flocks that were described as obscuring the sun on an otherwise clear day, and could take hours to pass. In 1810, Alexander Wilson, an American naturalist, guessed that a single migratory flock, perhaps 0.3 mi (0.6 km) wide and 89 mi (144 km) long, contained two billion birds. Many other impressions written by naturalists of those times also suggest that the passenger pigeon was an extraordinarily abundant bird.
Because passenger pigeons tended to migrate and breed in large, dense groups, it was easy for commercial hunters to kill them in large numbers and then sell the carcasses in urban markets. The passenger pigeon was slaughtered in enormous numbers using guns, clubs, nets, and smoke. The size of some of the hunts is astonishing, for example, in 1869 an estimated one billion birds inhabited Michigan alone. This intensity of exploitation, occurring at the same time as the destruction of much of its breeding habitat, proved to be unsustainable, and the passenger pigeon quickly declined in abundance. The last known nesting attempt in the wild occurred in 1894, and the last passenger pigeon died in a zoo in 1914.
The extinction of the passenger pigeon has become a metaphor for the sorts of damages that uncontrolled exploitation by humans can cause to even enormously abundant ecological resources.
See also Critical habitat.
Resources
BOOKS
Baskett, T., ed. Ecology and Management of the Mourning Dove. Harrisburg, PA.: Stackpole Books, 1993.
Brooke, M., and T. Birkhead, eds. The Cambridge Encyclopedia of Ornithology. Cambridge, UK: Cambridge University Press, 1991.
del Hoyo, J., A. Elliott, and J. Sargatal. Handbook of the Birds of the World. Vol. 4, Sandgrouse to Cuckoos. Barcelona: Lynx Edicions, 1997.
Freedman, B. Environmental Ecology. 2nd ed. San Diego: Academic Press, 1994.
Gibbs, D., E. Barnes, and J. Cox. Pigeons and Doves: A Guide to the Pigeons and Doves of the World. Tonbridge, UK Pica Press, 2001.
Skutch, A.F. The Life of the Pigeon. Ithaca, NY: Cornell University Press, 1991.
PERIODICALS
Gagliardo, A., et al. “Having the Nerve to Home: Trigeminal Magnetoreceptor vs. Olfactory Mediation of Homing in Pigeons.” Journal of Experimental Biology 209 (August 2006): 2888–2892.
Bill Freedman