Birds
Pigeon
Columbidae · also called dove, rock dove
The bird pecking at crumbs in a city square and the white bird released at a wedding are the same species, the rock dove. The dove family is old, widespread, and full of surprises: birds that feed their chicks on milk, birds that navigate home across country they have never seen, and, at the extremes, the turkey-sized crowned pigeons and the extinct dodo.
Overview
Pigeons are the family Columbidae, around 350 species, on every continent except Antarctica and most diverse in the forests of Southeast Asia and Australasia. “Pigeon” and “dove” are the same thing — loosely, bigger species get called pigeons. All are plump, small-headed, seed- or fruit-eating birds, and all feed their young on crop milk.
Milk and navigation
Both parents produce crop milk, a rich secretion from the crop lining, and feed the squabs on it, so pigeons can breed in any season. Homing pigeons, bred from the rock dove, find their loft from hundreds of kilometres away using the sun, the magnetic field, smell, infrasound, and learned landmarks — an ability used for message-carrying since ancient times.
City birds and giants
The city pigeon is a feral rock dove, nesting on ledges as its ancestors nested on sea cliffs. The family also produced the turkey-sized crowned pigeons and the flightless island dodo and solitaire, both hunted to extinction in the 1600s and 1700s.
Billions to zero
The North American passenger pigeon, once perhaps the most numerous bird on Earth, was hunted and deforested to extinction within decades, the last bird dying in 1914 — its huge-colony breeding system collapsed once numbers fell.
Status
Pigeons as a family are Not Evaluated, trend decreasing. A few adaptable species are abundant, but about a quarter of dove species are threatened, mostly fruit and ground doves on tropical islands, hit by habitat loss and introduced cats and rats. At least ten species have gone extinct in modern times.
Pigeon: common questions
What is the difference between a pigeon and a dove?
Nothing consistent. Both words are used for members of the same family, Columbidae, and there is no scientific line between them. In general English usage dove tends to be applied to the smaller, daintier species and pigeon to the larger and chunkier ones, so the small collared bird in a garden is a dove and the big grey city bird is a pigeon, but this is only a loose convention. The bird that symbolises peace and the bird that fouls a statue are the same species, the rock dove, also called the common pigeon. Different languages split the names differently, and some species are called dove in one country and pigeon in another.
How do homing pigeons find their way home?
They use several cues layered together, and researchers are still untangling exactly how. A pigeon released in unfamiliar territory appears to work out roughly where it is, the map step, using some combination of the Earth's magnetic field, the pattern of smells carried on the wind, very low-frequency sound from distant coasts and mountains, and possibly other signals. It then sets a heading, the compass step, using the position of the sun corrected for time of day, or the magnetic field when the sun is hidden. As it nears home it switches to familiar visual landmarks and learned routes. Training from progressively greater distances sharpens all of this.
Why are city pigeons so common, and are they a health risk?
City pigeons thrive because a city is, from a rock dove's point of view, an artificial landscape of cliffs, with building ledges to nest on, a year-round supply of spilled and discarded food, few predators, and the ability to raise several broods a year on crop milk regardless of season. As for health, pigeons can carry organisms that cause illness in people, but transmission is uncommon and mostly affects those with weakened immune systems or people with heavy occupational exposure to droppings in enclosed spaces. For the average person passing pigeons in a square, the risk is very low. The main practical problems pigeons cause are droppings that damage stonework and blocked gutters.
How did the passenger pigeon go extinct if there were billions of them?
Sheer abundance did not protect it, because the bird depended on being abundant. Passenger pigeons bred in vast dense colonies and foraged in enormous nomadic flocks, and this social system seems to have been necessary for successful breeding and for swamping predators. In the 1800s, expanding railways and telegraphs let commercial hunters find the colonies and ship dead birds to city markets by the wagonload, while the eastern hardwood forests that supplied their staple food of acorns and beech nuts were being cleared for farms. As numbers fell, the remaining birds could no longer form the huge colonies they needed, breeding collapsed, and the species crashed to extinction within decades, the last bird dying in 1914.