Feral pigeons are birds derived from domesticated populations of the rock dove (Columba livia), descendants that have escaped and are living independently from (and often unwanted by) humans. They are sometimes given the scientific names "Columba livia domestica" or "C. l. urbana", but neither of these subspecific names is accepted by any of the ornithological authorities like the IOC World Bird List or BirdLife International. They are also called city doves, city pigeons, or street pigeons,Nagy, Kelsi, and Johnson, Phillip David. Trash animals: how we live with natures filthy, feral, invasive, and unwanted species. Minneapolis (Minn.), University of Minnesota Press, 2013. and (locally, in Britain) skemmies ( skemmy). Wild rock doves, domestic pigeons, and feral pigeons are all the same species and will readily interbreed. Many domestic birds have been lost, escaped or been released over the years, and these gave rise to populations of feral pigeons.
Feral pigeons inhabit man-made structures such as buildings as a substitute for cliffs and other rock formations. Their domestic ancestry predisposed them to living near humans, and they subsequently became adapted to urban life, being abundant in towns and cities throughout much of the world. They are often described as a public nuisance, being a potential reservoir of disease and cause of property damage, through their habits and numbers. Many authorities and citizens consider them to be pests and an invasive species, often disparagingly referred to as "rats with wings". Actions are taken in many municipalities to lower their numbers or completely eradicate them.
Description
Feral pigeons are essentially the same size and shape as the original, wild rock dove, but often display far greater variation in colour and pattern than their wild ancestors owing to domestic ancestors. Their conformity to the wild phenotype's shape and size is considered to be the result of natural selection acting upon the population of now free-living birds, shifting the population closer to the form of their distant, wild ancestor. Local selective pressures have been suggested to explain the geographical variation across feral pigeons in the United States.
The blue-barred pattern which the original wild rock dove displays is generally less common in more urban areas. Pigeons feathers have two types of melanin (pigment) – eumelanin and pheomelanin. A study of melanin in the feathers of both wild rock and domestic pigeons, of different colouration types and known genetic background, measured the concentration, distribution and proportions of eumelanin and pheomelanin and found that gene mutations affecting the distribution, amounts and proportions of pigments accounted for the greater variation of colouration in domesticated birds than in their wild relations. Eumelanin generally causes grey or black colours, while pheomelanin results in a reddish-brown colour. Other shades of brown may be produced through different combinations and concentrations of the two colours. Urban pigeons tend to have darker plumage than those in more rural areas. Darker birds may be better able to store trace metals in their feathers due to their higher concentrations of melanin, which may help mitigate the negative effects of the metals, the concentrations of which are typically higher in urban areas.
Compared to their wild relatives, feral pigeons are unafraid of humans due to their long history of domestication, and are extremely trusting and tolerant of people.
The avoidance of mating between related individuals is ordinarily regarded as adaptive since it decreases the likelihood of inbreeding depression in progeny that can be caused by the expression of deleterious recessive alleles. However in feral pigeons it was found that despite detectable inbreeding depression, pairwise relatedness between mates was significantly greater than it was between nonmates. This suggests that mating with close kin provides inclusive fitness benefits that outweigh the costs of inbreeding depression.
Studies of feral pigeons in a semi-rural part of Kansas found that their diet includes the following: 92% maize, 3.2% oats, 3.7% cherry, along with small amounts of knotweed, elm, poison ivy and barley. They have been observed to eat insects and spiders. Pigeons tend to congregate in large, dense flocks when feeding on discarded food. In cities they typically resort to scavenging human garbage, as unprocessed grain may be impossible to find. Pigeon groups typically consist of producers, which locate and obtain food, and scroungers, which feed on food obtained by the producers. Generally, groups of pigeons contain a greater proportion of scroungers than producers. Feral pigeons can be seen eating grass seeds and berries in parks and gardens in the spring, but plentiful sources exist throughout the year from scavenging (e.g., food remnants left inside of dropped fast food cartons, in the form of popcorn, cake, peanuts, bread and currants) Food is also procured from waste bins. Bird feeders, often tourists or residents who feed pigeons, do so for reasons such as empathy, fun, tradition and as a means for social interaction.
Diseases Feral pigeons can be reservoirs and vectors of some human and livestock diseases, such as salmonellosis and tuberculosis. However, it is rare that a pigeon will transmit a disease to humans due to their immune system. Although feral pigeons pose sporadic health risks to humans, the risk is low, even for humans involved in occupations that bring them into close contact with nesting sites. Analysis revealed that feral pigeons harbored a total of 60 different human pathogenic organisms. Five pathogens were viruses, nine were bacteria, 45 were fungi, and one was a protozoan. However, only five pathogens were routinely transmitted to humans.
Pigeons often suffer injuries to their legs and feet due to contact with foreign objects in their environment, particularly hair or string, which gets wrapped around their legs and cuts off the blood supply, in some cases resulting in autoamputation.
Parasites Pigeons may harbour a diverse parasite fauna. They often host the intestinal helminths (parasitic worms) Capillaria columbae and Ascaridia columbae. Their ectoparasites include the ischnoceran lice Columbicola columbae, Campanulotes bidentatus compar, the amblyceran lice Bonomiella columbae, Hohorstiella lata, Colpocephalum turbinatum, the mites Tinaminyssus melloi, Dermanyssus gallinae, Dermoglyphus columbae, Falculifer rostratus and Diplaegidia columbae. The hippoboscid fly Pseudolynchia canariensis is a typical blood-sucking ectoparasite of pigeons in tropical and subtropical regions. The avian mites can infest human habitation and bite humans, a condition known as gamasoidosis. However, cases of them infesting mammals is relatively rare.
Pathogens Avian influenza (bird flu) has been extensively studied in pigeons. Studies have shown that adult pigeons are not clinically susceptible to nor carry H5N1, and that they do not transmit the virus to poultry. Other studies have presented evidence of clinical signs and neurological lesions resulting from infection but found that the pigeons did not transmit the disease to poultry reared in direct contact with them. Pigeons were found to be "resistant or minimally susceptible" to other strains of avian influenza, such as the H7N7. Three studies since the late 1990s were performed by the US Agriculture Department's Southeast Poultry Research Laboratory in Athens, Georgia, according to the center's director, David Swayne. The lab has been working on bird flu since the 1970s. In one experiment, researchers squirted into pigeons' mouths liquid drops that contained the highly pathogenic H5N1 virus from a Hong Kong sample. The birds received 100 to 1,000 times the concentration that wild birds would encounter in nature. "We couldn't infect the pigeons", Swayne said. "So that's good news."
Chlamydophila psittaci is endemic among pigeons and causes psittacosis in humans. It is generally transmitted from handling pigeons or their droppings (more commonly the latter). Psittacosis is a serious disease but rarely fatal (less than 1%).
Pigeons are also important vectors for various species of the bacteria Salmonella, which causes diseases such as salmonellosis and paratyphoid fever. There were single case incidences for transmission of Salmonella enterica.
Pigeons are not a major concern in the spread of West Nile virus: though they can contract it, they apparently do not transmit it to humans.
Avian paramyxovirus (PMV) is carried by pigeons and is a serious affliction in birds.
Impact
Feral pigeons often only have small populations within cities relative to the number of humans. For example, the breeding population of feral pigeons in Sheffield, England, in summer 2005 was estimated at 12,130 individuals (95% confidence interval 7757–18,970), in a city with a human population of about 500,000. Despite this, feral pigeons usually reach their highest densities in the central portions of cities, so they are frequently encountered by people, which may lead to conflict.
Pigeons can compete with native birds for nest sites, which could become a conservation issue for seabirds.
The scarcity of the wild rock dove is largely due to interbreeding with feral birds.
Faeces Healthy, well-fed pigeons excrete faeces that are composed largely of a brown to greenish-brown mass with a white cap; the white cap is composed of uric acid crystals, with some of the uric acid dissolved within urea that comprises the liquid urine, which is transparent and often absorbed by the mass of solid waste of the faeces, which maintains its shape when the bird is in good health. The colour of the resultant faecal matter is helpful in diagnosing the condition of the bird; droppings which appear dull yellow are indicative of starvation, especially if watery; green may be a sign of liver disease due to an abundance of excreted biliverdin, bright green being an abundance of passed bile implying bowel problems or not having eaten recently; and red-brown showing kidney disease.
Contact with pigeon droppings poses a minor risk of contracting histoplasmosis, cryptococcosis and psittacosis. Pigeon faeces has been implicated as a "contributing factor" of a cryptococcus infection leading to the death of a child.
Feral pigeon faeces cause substantial economic losses from property damage, often considered to be from their corrosive droppings damaging stone edifices and metal structures.
Protection status
In the United Kingdom, pigeons are covered under the "General Licences" and can be humanely culled by the land owner or their agent for a variety of reasons including spread of human disease. It is illegal to kill/destroy nests for any reason other than those listed under the general licences.
In the U.S., the Migratory Bird Treaty Act of 1918, which protects native birds, does not apply to feral pigeons, common starlings or house sparrows, because they are introduced species. It is usually legal to kill feral pigeons in the United States; methods such as poisons may be regulated, however. Pigeons are labeled an invasive species in North America by the USDA.
In India, pigeons are protected under Section 428 and Section 429 of the Indian Penal Code. Wild pigeons are further protected under the Wildlife Protection Act, 1972.
Control methods
Predators
Peregrine falcons Falco peregrinus, which are also originally cliff dwellers, have also adapted to the skyscrapers of large cities and often feed exclusively on feral pigeons. Some cities actively encourage this through falcon breeding programs. Projects include the Unibase Falcon Project and the Victorian Peregrine Project. Other species of falcons have also been observed to hunt down ferals.