Feral pigeons are derived from domestic pigeons that have returned to the wild. The domestic pigeon was originally bred from the wild Rock dove, which naturally inhabits sea-cliffs and mountains. Feral pigeons find the ledges of buildings to be a substitute for sea cliffs, and have become adapted to urban life and are abundant in towns and cities throughout much of the world.
All pigeons are one species (columba livia). Pigeons breed when the food supply is good, which in cities can be any time of the year. Laying of eggs can take place up to six times per year. Pigeons mate for life, and are often found in pairs during the breeding season, but usually the pigeons are gregarious preferring to exist in flocks of from 50 to 500 birds.
Nests are rudimentary, similar to other ground or cliff nesting birds. Abandoned buildings are favorite nesting areas. Mass nesting is common as pigeons are a community flocking bird, often dozens of birds will share a building. Loose tiles and broken windows give pigeons access; they are good at spotting new access points, for example following property damage caused by strong winds. Pigeons are particularly fond of roof spaces. These often contain water tanks. Any water tank or cistern on a roof must therefore be secured and sealed off to keep the pigeons out of them. On undamaged property, the gutters, window air conditioners and empty air conditioner containers, chimney pots and external ledges are used as nesting sites. Many building owners try to limit roosting by using bird control spikes and netting to cover ledges and potential nesting places on buildings. This has little effect on the size of the pigeon population, but it can reduce the accumulation of droppings on and around a particular building location.
Feral pigeons can be seen eating grass seeds and berries in parks and gardens in the spring, but there are plentiful sources throughout the year from scavenging (e.g., dropped fast-food cartons) and they will also take insects and spiders. Further food is also usually available from the disposing of stale bread in parks by restaurants and supermarkets, from tourists buying and distributing birdseed, etc. Pigeons tend to congregate in large, often thick flocks when going for discarded food, and many have been observed flying skilfully around trees, buildings, telephone poles and cables, and even moving traffic just to reach it.
Many city squares are famous for their large pigeon populations, for example, the Piazza San Marco in Venice, and Trafalgar Square in London. For many years, the pigeons in Trafalgar Square were considered a tourist attraction, with street vendors selling packets of seeds for visitors to feed the pigeons. The feeding of the Trafalgar Square pigeons was controversially banned in 2003 by London mayor Ken Livingstone. However, activist groups flouted the ban, feeding the pigeons from an area south of Nelson’s Column in which the ban does not apply. They eventually agreed to feed the pigeons only once a day, at 7:30 a.m.
Feral pigeons are often considered a pest or even vermin, owing to concerns that they spread disease (however, it is rare that a pigeon will transmit a disease to humans due to their immune system). While pest exterminators use poison, hawks and nets have also been employed at ground level to control urban pigeon populations, though this generally achieves only a limited, temporary effect. Long-term reduction of feral pigeon populations can be achieved by restricting food supply, which in turn involves legislation and litter (garbage) control. Some cities have deliberately established favorable nesting places for pigeons – nesting places that can easily be reached by city workers who regularly remove eggs, thereby limiting their reproductive success. In addition, pigeon populations may be reduced by bird control systems that successfully reduce nesting sites.
Peregrine Falcons which are also originally cliff dwellers have also adapted to the big cities, living on the window ledges of skyscrapers and often feeding exclusively on pigeons. Some cities actively encourage this through falcon breeding programs. Larger birds of prey occasionally take advantage of this population as well. In New York City, the abundance of pigeons (and other small animals) has created such a conducive environment for predators that the Red-Tailed Hawk has begun to return in very small numbers, the most famous of which is Pale Male, who lives near Central Park (bird watchers have followed him since he was hatched in 1990).
The use of poisons has been proven to be fairly ineffective, however, as pigeons can breed very quickly — up to six times a year — and their numbers are determined by how much food is available; that is, they breed more often when more food is provided to them. An additional problem with poisoning is that it also kills pigeon predators. Due to this, in cities with Peregrine Falcon programs it is typically illegal to poison pigeons. A more effective tactic to reduce the number of feral pigeons is deprivation. Cities around the world have discovered that not feeding their local birds results in a steady population decrease in only a few years. Pigeons, however, will still pick at garbage bags containing discarded food or at leftovers carelessly dropped on the ground. Feeding of pigeons is banned in parts of Venice, Italy.
In 1998, in response to conservation groups and the public interest, the National Wildlife Research Center, a USDA laboratory, started work on nicarbazin, a promising compound for avian contraception. Avian contraception has the support of a range of animal welfare groups including the Humane Society of the United States, the ASPCA, and PETA. USDA continues to develop wildlife contraceptives for deer, birds, and small mammals. The new field of wildlife contraceptives is developing rapidly and promises humane management of animal populations.
The Daily Omnivore 
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