Because they’re born, live and die in the middle of an enormous city, teeming with people, dogs, cats (who are ruthless little predators), falcons (who love a nice fat pigeon), rats and squirrels—who compete with them for food—and motor vehicles. Timid birds are the last to the table. But at the same time, their urban environment is full of food and because pigeons are a kind of rock dove, full of suitable places to nest; most buildings have window ledges, many have ornamental stonework that lends itself to tucking a nest into the nooks and crannies, and window/through-the-wall air-conditioners, many of them with some kind of ledge underneath, the perfect place to build a nest that’s sheltered from rain and predators. They’re accustomed to a noise level that would terrify non-urban birds—the even prowl subway el stations because they know people are always throwing away half eaten french fries and bagels and fried chicken scraps (yes, I’ve seen pigeons eating fast-food chicken). And there are plenty of people who feed pigeons and English sparrows, which for all their tininess are tough little bastards; I once saw a group of them chase away a swan so they could eat its food and swans are huge (they look serene on the water, but they’re big birds—think 25 pounds wit beaks and claws—and aggressive if you’re between them and something they want) by pecking at its huge, scaly godzilla feet. So big cities are a good place for birds with some stones.