Gray and inconspicuous they may be, but pigeons are highly adaptable and their numbers are surging around the world, heightening the risk of disease. Cities have resorted to imaginative techniques to kill the birds over the years, but the only effective curb is to stop feeding them, says a Swiss scientist.
The pigeon is a heavenly symbol of peace, love and purity but it also produces 12 kilos of excrement a year and is widely decried as a flying rat that soils facades and spreads disease in cities all over the world.
Scientists, city officials and animal welfare activists met in the western German city of Essen on Tuesday for Germany's first Town Pigeon Conference to discuss how to deal with the growing pigeon population which is expected to rise by around 50 million to up to 400 million worldwide in the next 10 years as a result of growing urbanization.
The pigeon derives from the rock dove and was one of the first animals to be domesticated, some 10,000 years ago, in the Middle East. There are around 300 varieties of the bird. It was initially bred to be eaten, and its excrement, guano, was a prized fertilizer.
The inconspicuous gray bird with a fatty neck has adapted better to life in urban public areas than any other animal, and its presence is truly global.
There are around one million of them in New York, and Venice has the highest pigeon density with an estimated three birds per human inhabitant. In most big European towns, there is around one pigeon for every 20 citizens.
"Pigeons have had a gigantic career as a symbol of love, of marital fidelity, of peace," Professor Daniel Haag-Wackernagel, a biologist at the University of Basel who has studied pigeons for decades, told SPIEGEL online. "Historically it has such a positive, heavenly image that killing the bird is still regarded as immoral and unethical by many."
Throughout history, pigeons have found plentiful food close to where humans live, either by being fed directly or eating spilt horse feed, or by picking up rubbish that had gathered in the cracks of the cobblestones that were commonplace in medieval European towns, said Haag-Wackernagel.
Their population exploded in the 20th century as food became ever cheaper in relation to personal income. The bird is supremely adaptable, finding breeding places in all kinds of unnatural locations ranging from air conditioning vents to warm satellite dishes. Their diet, originally grain-based, has also evolved and town pigeons now eat virtually everything from discarded beef burgers to human vomit.
Major cities have been trying to reduce their pigeon populations since the early 20th century and have resorted to a colourful variety of methods including straight poisoning, shooting, firing nets over flocks with rockets, blasting them with salt pellets and even by means of an "electric chair:" placing food on a high-voltage metal platform to fry the birds alive.
Contraception pills have also been attempted, but they can poison other animals. "Scaring" is another method - London has resorted to Harris hawks and loud megaphones to drive pigeons away from Trafalgar Square. But that technique just moves them to other parts of the city. London has also started fining people for feeding pigeons in the square.
"Killing makes no sense at all," says Haag-Wackernagel. "The birds have an enormous reproduction capacity and they'll just come back. There is a linear relationship between the bird population and the amount of food available." A pair of pigeons can produce up to 12 fledglings per year.
"The best way to reduce the population is not to feed them. People say it's cruel to deprive them of food but in the wild the sudden absence of food is a completely natural occurrence and animals adapt to it."
Haag-Wackernagel developed a scheme for the city of Basel in the 1980s which resulted in a decline in the pigeon population by two thirds in four years. "We launched a campaign to persuade people not to feed the birds. We never put a ban on feeding because that always creates martyrs. We think you have to convince people."
The scheme included setting up nine pigeon lofts in the attics of churches and schools where breeding boxes were installed. "We didn't feed them there and we took some of their eggs away," said Haag-Wackernagel. Depriving pigeons of food also slows down their reproduction because it forces them to devote more time looking for food rather than breed, he said.
The western German town of Moers has come up with a less rigorous scheme. For the past three years it has been recruiting unemployed people as "Pigeon Wardens" to construct and clean out public pigeon coops and feed the animals.
Pigeons still enjoy a considerably better reputation than rats, which suffered a lasting PR setback by spreading the Black Death.
But the birds can and do spread diseases, allergies and parasites to humans. Haag-Wackernagel says many everyday illnesses including allergies can be attributed to human proximity to the birds which carry salmonella, lung illnesses, fleas, ticks and a host of other ailments -- something to think about when surrounded by flapping pigeons in town squares or outdoor cafes.
Pregnant women, children, the elderly and people infected with HIV are particularly at risk from contact with pigeons, said Haag-Wackernagel.
Reducing pigeon populations also gives the birds a better quality of life -- less stress and less cramped living conditions, says Haag-Wackernagel. But die-hard pigeon-fanciers remain unconvinced. "One man in Basel kept on feeding pigeons between 12 and 15 tons of pigeon food per year until he died aged 89."