Some people love them.

"Everybody thinks that they're dirty and nasty, but they're actually not."

"They're a dove."

"All they are is doves."

"Ah, you're a dove."

Other people, not so much.

"I hate them."

"They get way too close."

"I don't let people into the personal space that pigeons get into."

"They're just aggressive."

But whatever your stance may be, if you live in a city, you have to deal with them.

While pigeons are clearly at home in American cities like New York, they're actually native to seaside cliffs halfway around the world, in North Africa, the Middle East, and Europe, where we domesticated them 5,000 years ago.

At first, we farmed them for a source of protein, like chicken.

Then we bred them as messengers.

In the eigth century BC, for example, the Greeks used pigeons to send results from the Olympic Games to nearby towns.

And by the 16th century, pigeons had reached the ultimate peak.

Hobbyists began breeding the birds for show.

Akbar the Great, for example, reportedly had 10,000 show pigeons in his personal collection.

Suffice it to say, humans and pigeons were inextricably linked.

And that's why Europeans who migrated to North America in the 1600s brought some of these birds with them.

And surprise, surprise: "They escaped, and that's kind of what formed these feral populations in cities around the world."

That's biologist Elizabeth Carlen, who studies pigeons at Fordham University.

Once pigeons escaped, their population exploded, especially in cities.

Because, as Carlen says, cities are essentially tailor-made for these birds.

For one, pigeons can thrive on human food, unlike, say, robins or cardinals.

"What we have here is pigeons eating it looks like rice and bagels and probably doughnuts in there as well, and that ability to consume all this food waste has really made them very successful in cities."

But it's not just our leftovers they're noshing on.

We also feed them.

"Spike."

"That's Spike."

As a result, pigeons spend a lot less time searching for food and a lot more time breeding, which they can actually do without trees.

In their native range, pigeons nest on rocky seaside cliffs.

"And cities often mimic that by having tall buildings and by having places for pigeons to nest within that, such as fire escapes or AC units or even just ledges that are built in decoratively on the building all mimic those cliffs."

But there's another reason why pigeons are so successful in cities.

They're incredible navigators.

Some of these birds can find their way home from nearly 1,000 kilometers away.

And those navigation skills serve them well in a complex cityscape.

“That is likely linked to their ability to find food within the city and know where food sources previously were and go and check on those food sources.”

So how many pigeons live in cities anyway?

In New York there's an adage: one pigeon for every person.

That would be more than 8 million birds.

And whether or not that's true, urbanites have decided on one thing: The city isn't large enough for the both of them.

"I got nothing for them."

"I don't got food. I don't got money. I got nothing."

“Leave me alone.”

In 2003, for example, things got so bad in New York's Bryant Park that a professional falconer was hired to scare them away.

And it's not just American cities.

In Bangkok for example, officials have considered imposing jail time for people who feed the birds.

But here's the thing: As long as we have thriving cities, pigeons will live in them.

In fact, the only thing that might control their populations, aside from cleaning up, is natural predators.

"For a long time, pigeons didn't have natural predators within cities."

That's thanks in part to the insecticide DDT, which Americans started using in the 1940s.

"The use of DDT made eggshells very thin and decreased the population of raptors such as peregrine falcons and Cooper's hawks and red-tailed hawks."

But in 1972, the Environmental Protection Agency banned DDT, and as a result: "Those predators are now moving back into the city."

And with so much to eat, they probably won't be leaving anytime soon.