Take a walk in almost any urban city in the world, and you’re likely to encounter a pigeon — or 10. They zoom down streets between high rise buildings; they coo at you as you enter doorways; and they waddle down the pavement in front of you, almost in your way . They’re never too far from your feet as you munch on a snack in the park, always ready to scoop up your crumbs when you aren’t looking; and never far from spilled trash outside a restaurant. If you live in an urban apartment, you might even spot a pair building a nest on your air conditioner or fire escape.

In fact, there are about 400 million pigeons around the world, most of them living in urban cities. They’re all the same species of bird — even if they vary in color sometimes — whether you spot them in London, Rome, New York City or Miami. These birds are so prominent that they’ve been labelled “rats with wings” because in most places outside their historical habitat of the Mediterranean and the Middle East, they are an invasive, non-native species. And like rodents, they thrive in urban environments, replacing other native species when humans develop and build.

So what is it about this bird that makes it so adept at living in these busy cities? After all, it’s not like urban environments are that easy a place to live.

“Cities seem to be these inhospitable environments,” says Elizabeth Carlen, a doctoral student at Fordham University who is researching the evolution of urban pigeons. “Cities are loud. There’s light pollution. There’s tons of environmental toxins.”

Pigeons in Washington Square Park in New York City. (Photo Credit: Artur Debat/Getty Images)

It’s also not like there aren’t urban predators. In New York city, for example, peregrine falcons and hawks regularly hunt pigeons. Owls, cats and other scavengers will also eat them. In the southern French town of Albi, as any viewer of the Planet Earth II series likely remembers, catfish leap out of the water to snatch and devour these birds if they stop for a drink of water. Plus, humans — along with our vehicles and litter— are a threat to them.

“A lot of pigeons are missing toes,” Carlen says, “which is usually because something like string, or synthetic hair from wigs made out of plastic, gets wrapped around their toes and amputates them. That happens because they spend a lot of time walking around.”

Nevertheless, she continues, “pigeons are in every city that I’ve ever been to and they seem to be doing really well.”

The answer to why they are so adept at living alongside of us humans seems to be, at least in part, because of their history.

All urban pigeons are descended from the rock dove, or Columba livia, a bird that lived in rocky, coastal cliff habitats. But as early as 10,000 years ago, humans in ancient Mesopotamia (modern day Iraq) and Egypt began lurring the birds away from the coast so that they could eat them. Soon, the birds were domesticated and bred for food. The young birds — known as “squabs” — were a popular delicacy.

“Then, when other poultry became more popular, like chicken, pigeons kind of fell out of favor,” Carlen explains. “So people started breeding pigeons as a hobby.”

(Photo credit: Jewel Samad / AFP / Getty Images)

People bred them for their particular characteristics — such as racing ability — or for special physical traits. Because pigeons have great navigation skills, endurance, keen eyesight and a docile nature, they were often used as messengers. For example, Mediterranean sailors used them to point a lost ship towards land and in 776 B.C., it is said that a pigeon delivered the results of the first Olympic games. In the 1600s, Europeans brought them over to North America on ships.

Of course, over time, these domesticated pigeons escaped their human handlers and struck out on their own. Because the birds were bred for year round egg production, they reproduced quickly. One pair can produce up to 10 chicks a year, according to the BBC.

In addition, because they were reared to have a strong attachment to their territories as messengers, they didn’t go far from human towns and cities once they escaped.

Urban areas were also advantageous to them because they could scavenge human food. “As with most animal domestication, the individuals with the highest tolerance for humans had the greatest access to food, which in turn led to reproductive advantages and a growth in populations,” notes a paper in the Journal of Urban Ecology. In other words, because pigeons don’t overly fear humans, they’re quite happy to scavenge for food even when people are nearby.

“Being able to eat all kinds of different food — or food waste — opens up a lot of opportunity for them,” Carlen says. “Especially if you are able to grab that food quickly when it is dumped out and [physiologically,] pigeons are able to consume a lot of food quickly.”

“Then they’ll just sit around and digest it afterwards.”

In addition, according to LiveScience, well-fed pigeons are able to produce a protein- and fat- rich milk in a throat pouch called the crop. This enables them to rear their chicks with this milk instead of having to find additional food — notably insects, worms or seeds — as other birds do for their young.

Human cities also provided good nesting grounds for the birds. “The architecture of our cities artificially mimics their original natural habitat,” says Carlen. “Big buildings mimic those rocky cliffs they once nested on.” For example, window sills, ornate building facings, air conditioning units and bridges all provide crevice-like perches for nests. This fact made city living “up their alley,” so to speak.

Pigeons perch along the arm of a traffic light in New York City. (Photo Credit: Timur Emek/Getty Images)

Pigeons also flock together to look for food as a group as well as to gain some safety in numbers from predators. “They have little calls and certain behaviors that might signal to the other pigeons ‘I’m taking off but it’s okay, you’re fine’ or ‘we should all take off right now,’”says Carlen. “That’s why when a flock of pigeons gets startled, they’ll all take off together.

There is also some evidence, according to a 2014 study, to suggest that pigeons with darker plumage might be better at surviving in cities because melanin pigments in darker feathers binds to trace metal ions that they are exposed to from urban living. This could help the birds sequester those harmful trace metals in their coat.

However, while all of these factors — including their diet, their nesting habits, their breeding biology, their behavior — help partially explain why pigeons are so successful at living in cities, there is still a lot that we don’t know about the birds because, despite their prevalence, they’re not that well researched by scientists.

“It’s always surprising to me that so few people are working on them,” says Carlen. “Maybe they don’t find them that exotic or maybe, because we see them everyday, they think we have all these answers about them.”

But in reality, there are lots about pigeons, their evolution, and their adaptations that we simply don’t know. In fact, that is why University of Montana researcher Stella Capoccia and some of her colleagues made a plea in the Journal of Urban Ecology for more research.

Carlen continues, “One of my biggest shocks coming into pigeon research is: ‘how do we not know this already?’” Maybe it’s time we get to know our city neighbors better.

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