In quite a few cities, a square covered in pigeons is far less surprising than an empty one. Take Milan, for instance; expecting to see at least a few of them in Piazza del Duomo is a pretty safe bet. The same goes for St. Mark's Square in Venice, where the situation got so bad, pigeon feeding had to be officially banned, to the great sadness of the birdseed vendors in the square.

“It’s a tradition,” one of them told The New York Times, “It’s like removing Rialto or The Bridge of Sighs”—two of the main attraction points in Venice for both tourists, and, likely, pigeons.

But what, apart from the obvious—birdseed—led flocks of these googly-eyed birds into the cities in the first place?

Bored Panda turned to the evolutionary biologist Robert Montgomerie to discuss the reasons some animals, including different species of birds—among which, of course, pigeons—ended up living alongside people in cities. The expert pointed out four main factors, one of them being warmth, as the cities are warmer due to concrete and asphalt, among other things.

“There are also fewer predators,” the expert continued, adding that it applies when it comes to big predators, as the cities are now full of the smaller ones, such as foxes, falcons, and raccoons.

The third reason is nest sites. “Pigeons, swallows, falcons, house sparrows, starlings and some other species all nest on buildings, which are much more plentiful than their natural sites on cliffs and tree hollows,” he explained.

Last but not least, there’s food, which they can get either by feeding at bird feeders and people’s hands, garbage, insects in gardens, or scraps that people discard while eating outside. “I once watched ibises (bin chickens) snatch sandwiches from unsuspecting picnickers in Sydney, Australia,” the expert recalled. “Clearly this was easier pickings than hunting for unsuspecting frogs in marshes.”

Another reason why some birds might end up in cities, according to Professor Peter Paton, is their resemblance to the natural environment the winged creatures are used to. “Pigeons are native to cliffs, so possibly city buildings mimic their native habitat,” he pointed out. “They were slowly domesticated over time and evolved a commensal relationship with humans, so ended up in cities.”

The expert added that they are arguably easier to domesticate than other birds, which is why they are adapted to living with humans more so than most other species.

Even though pigeons seem to have adapted to the city lifestyle quite well, certain instincts affect their habits even in the concrete jungle. For instance, the fact that they tend to move around in flocks.

“It’s about safety in numbers. An anti-predator strategy,” Paton said. “Pigeons are common prey to raptors, such as falcons, and when you are in a large flock, it is easier to evade predators, as more eyes are watching out for them. Also, in a large flock, it’s more likely that a neighbor will be eaten rather than you.”

“There are lots of animals and birds that move around in social groups outside the breeding season, either for enhanced vigilance for predators, or finding food; or, more rarely, for sussing out potential mates for the next breeding season,” Montgomerie suggested.

Quite a few species on this list are among those who travel in groups, such as monkeys, cockatoos, and cats, just to name a few.

But with all sorts of species charting human-filled territories, is it likely that animals are becoming less and less fearful? Prof. Montgomerie does not think that’s the case; not in the natural world, at least. “This may be true of animals in cities but in the countryside, animals and birds seem to be most wary where they have regular contact with humans and are tamest on remote islands and in the arctic where humans are relatively scarce.”

Even though not to the same extent as the Arctic, Alaska is another place where people are relatively scarce; but ‘pigeons’ are not. Except ‘pigeons’ in Alaska are not the same as those roaming the streets in Italy.

As quite a few pictures on this list show, an eagle is the bird that can be as commonly seen in Alaska as pigeons are elsewhere. As a matter of fact, the bald eagle population there is reportedly greater than in all of the lower 48 states combined, according to the Forest Service. The birds seemingly thrive there not only because of fewer people, but also because of the condition of their natural habitat and abundance of food.

That’s why if Home Alone 2 was set in Alaska, the kind-hearted Pigeon Lady would likely be feeding a very different kind of bird. (And have a different moniker, too.)

Even though in some cities it feels like there are more pigeons than people, they are not the most populous species of bird out there; they succumb in number to their distant relative, the chicken. It is believed that the pigeon and chicken lineages diverged more than 85 million years ago, which led to the former becoming the most abundant bird worldwide, with a population reaching 30 billion. The pigeon—well, its cousin, the dove, to be exact—is third on the list with a population of 475 million.

Whether you find pigeons fascinating or not really, you might want to check out the beautiful variety on this list here, featuring some rather impressive-looking breeds. For more random pigeon-related content, check out Bored Panda’s pieces on this Japanese woman’s pigeon shoes or sing along while browsing the comics depicting a pigeon rendition of The Killers’ ‘Mr Brightside’.