[Narrator] Pigeons.
Some people love them.
Larry: 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. Ah.
[Narrator] Other people, not so much.
Man: I hate 'em.
They get way too close.
I don't let people into the personal space
that pigeons get into.
They're just aggressive.
[Narrator] 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 8th 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,
Elizabeth Carlen: They escaped, and that's kind of what
formed these feral populations in cities around the world.
[Narrator] 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.
Carlen: 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.
[Narrator] But it's not just our leftovers
they're noshing on.
We also feed them.
Larry: Spike.
That's Spike.
[Narrator] 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.
Carlen: 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.
[Narrator] 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.
Carlen: That is likely linked to their ability
to find food within the city
and know where food sources previously were
and go and check in those food sources.
[Narrator] 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.
Man: I got nothin' for them.
I don't got food. I don't got money. I got nothin'.
Leave me alone.
[Narrator] 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.
Carlen: For a long time, pigeons didn't have
natural predators within cities.
[Narrator] That's thanks in part to the insecticide DDT,
which Americans started using in the 1940s.
Carlen: 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.
[Narrator] But in 1972,
the Environmental Protection Agency banned DDT,
and as a result,
Carlen: Those predators are now
moving back into the city.
[Narrator] And with so much to eat,
they probably won't be leaving anytime soon.