Feral pigeon

Feral pigeons are widely considered pests, and can be reservoirs and vectors of some human and livestock diseases, such as salmonellosis and tuberculosis.[20][21] However, It is rare that a pigeon will transmit a disease to humans due to their immune system. [21]Although feral pigeons pose sporadic health risks to humans, the risk is real, 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. There were single case incidences for transmission of Salmonella enterica. [22]

Many places where feral pigeons could land are covered with spikes.

Pigeons often cause significant pollution with their droppings, though there is little evidence of them driving out other bird species. Pigeons are labeled an invasive species in North America by the USDA.[14]

Peregrine falcons, which are also originally cliff dwellers, have too adapted to the skyscrapers of large cities and often feed exclusively on rock doves.[23] Some cities actively encourage this through falcon breeding programs. Projects include the Unibase Falcon Project and the Victorian Peregrine Project.

Other predators of the pigeon have been recorded, including Eurasian sparrowhawks, crows and gulls.[24][25][26] In London, the population of Great white pelicans at St. James's Park have also been recorded killing and consuming pigeons despite alternative food sources being available.[27][28] In cities in Western Europe, European herring gulls may occasionally hunt and consume feral pigeons in addition to other birds and small mammals.[29]

Larger birds of prey occasionally take advantage of this population as well. In New York City, the abundance of feral 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, including the notable Pale Male.

Due to their non-selective nature, most avian poisons have been banned. In the United States market, only 4-aminopyridine (Avitrol) and DRC-1339 remain registered by EPA. DRC-1339 is limited to USDA use only, while 4-AP is a restricted-use pesticide, for use only by licensed applicators.

The use of poisons has been proven to be fairly ineffective, however, as pigeons can breed very quickly, and their numbers are determined by how much food is available; that is, they breed more often when more food is provided to them. When pigeons are poisoned, surviving birds do not leave the area. On the contrary, they are left with more food per bird than before. This attracts pigeons from outside areas as well as encouraging more breeding, and populations are re-established quickly.[30] 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.[23]

A man feeding feral pigeons at Esplanadi in Helsinki, Finland in 1921

One of the difficulties of controlling feral pigeon populations is the common practice of feeding them, as here in New York City.

A more effective tactic to reduce the number of feral pigeons is deprivation.[31] Cities around the world have discovered that not feeding their local birds results in a steady population decrease in only a few years. As scavengers, pigeons will still pick at garbage bags containing discarded food or at leftovers carelessly dropped on the ground, but securely disposing of foodstuffs will greatly reduce scavenger populations. Feeding of pigeons is banned in parts of Venice, Italy.[32]

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.[4] In addition, pigeon populations may be reduced by bird control systems that successfully reduce nesting sites.

In 1998, in response to conservation groups and the public interest, the National Wildlife Research Center (NWRC), a USDA/APHIS laboratory in Fort Collins, Colorado, started work on nicarbazin, a promising compound for avian contraception. Originally developed for use in resident Canada geese, nicarbazin was introduced for use as a contraceptive for feral pigeons in 2007.

The active ingredient, nicarbazin, interferes with the viability of eggs by binding the ZP-3 sperm receptor site in the egg.[33] This unique contraceptive action is non-hormonal and fully reversible.[34]

Registered by the EPA as a pesticide (EPA Reg. No. 80224-1), "OvoControl P", brand of nicarbazin, is increasingly used in urban areas and industrial sites to control pigeon populations. Declared safe and humane, the new technology is environmentally benign[35] and does not represent a secondary toxicity hazard to raptors or scavengers.[36]

Avian contraception has the support of a range of animal welfare groups including the Humane Society of the United States, the American Society for the Prevention of Cruelty to Animals and People for the Ethical Treatment of Animals. Avian contraceptives are also perceived by civilians as an acceptable method for population control, over other methods such as prohibition to feeding or extermination.[37]

Large pigeon trap/coop/loft at Batman Park, Melbourne. Designed specifically to encourage nesting and allow removal of fertilised eggs to prevent population growth, it was a landmark in its own right before its removal, for lack of success, around 2015.

When eggs are removed in artificial pigeon houses, the interval between reproductive attempts is strongly reduced, which reduces the efficiency of the method.[38] Dummy egg nesting programs have therefore been tested in some cities with mixed results. There, the eggs are removed and replaced with dummy eggs. The real eggs are then destroyed. One such structure, in Batman Park in Melbourne, Australia, was unsuccessful in attracting pigeons and has since been removed.[39][40] The loft used in Melbourne was on stilts, with a cage door allowing access from beneath for accessing the structure at night when the pigeons are asleep.