One reason that pigeons do so well in cities might be indicated by thier real name: Rock Doves. They live on the rocks, or cliffs. Concrete is really artificial stone, and human structures are just what rock doves need to roost. Parking garages are especially nice, they have many nooks and crannies in which to lay eggs and raise chicks. They also like building nests under bridges. In Rosslyn, a suburb of Washington, DC, pigeons may be observed sitting on eggs on the pylons which support the pedestrian bridges between buildings.
Another reason that pigeons do well in cities is their relationships with humans. Common wild pigeons actually have much ancestry from domestic pigeons, which are quite tame. Perhaps that's why they have almost no fear of humans. If you approach a pigeon, It will only avoid you if you are too close. Some pigeons are so lazy that they will only avoid you to prevent you from stepping on them by accident. will often only fly away if they are cornered, or if you are extremely close. This is a good strategy, since most humans don't try to harm them, so if the pigeon turns chicken, it's usually just wasting energy while all the other pigeons are eating the scraps that it flew away from.
Well, with all of these lazy pigeons walking about, I was tempted by a question. Can a heavy, large human, which obviously can't fly, catch an agile, flying pigeon? Yes, it's possible, I have done it. I realized, that a pigeon sitting on a table won't fly away until you are a certain distance from it. This distance was less than the length of my arms. The general approach was to get near enough to the pigeon, and them to abruptly reach and grab it. I tried until I caught one. I soon released the panicky bird, which flew away very fast. That was the last pigeon I ever caught this way. From that point on, every time I near a pigeon, It flys away well before I come within arm's reach. Not just the one I caught, but any of them! Pigeons aren't as dumb as they look. After about 2 weeks of harrassing pigeons in this manner, I noticed something that might make the restaurant that owns those outdoor tables happy; There were fewer pigeons on the tables. They had learned that that was a danger zone.
Pigeons are adept learners; they can make associations between what they see and whether or not they can take advantage of the situation. One day I was walking in Rosslyn's Metro park, and a paused by the subway elevator. Suddenly the air was thick with pigeons, which landed at my feet and all looked at me, as if I was going to feed them. On another occasion, I witnessed this happen to an old man who said "What the hell do you want! I aint got nothing". What I believe happened was that the pigeons were accustomed to being fed by someone standing at this site, so whenever anyone stops there long enough, the pigeons follow thier training and go to be fed. I believe the original stimulus is that the Circle of Pigeon Summoning is where the local Burger King dumps excess sesame seeds, which always provide a rich feast for the pigeons.
One game you can play with the local park pigeons is to 'remote' control them, like toy cars. When you get too close to a pigeon, with will walk directly away from you. You can steer it by walking towards one side of the pigeon. Since it will always walk with it's tail towards you, you can make it go just about anywhere on a flat open space. If you corner it, it will fly away. If you get too close it will fly away. I tried to herd one up stairs, but it regarded that as being cornered and just flew off. In most cases, the pigeon will just fly to another nearby spot on the ground, and you can continue herding it.
The most noteworthy thing about pigeons to most people is just how many of them there are. In Rosslyn, the pigeon flock is massive, dwarfing even the always numerous starling flocks. Why? Because Rosslyn, like many other urban areas is a perfect place for pigeon to flirt, get married, and raise a family; it all starts with a kiss. This may seem silly, but pigeons pair up and raise families according to what many call 'traditional family values', they're just a lot more productive than humans. Pigeons, like doves, can produce food (called 'pigeon milk' by pigeon breeders) for their young. Pigeons will feed each other this way to form a pair bond. It looks a lot like passionate kissing, and usually precedes pigeon sex. Another human-like attribute of pigeons is their co-operation in raising families; they take turns incubating eggs and caring for chicks. Many other birds a like this, which makes them in one way more 'human' than our closest relatives the chimps. Chimps are never monogamous, and the variety closest related to humans behave more like 'summer of love' teens than mature adult humans. Why would pigeons have 'family values' and chimps don't? Because bird eggs, like human babies, require constant attention, and are utterly helpless. Baby chimps, on the other hand can survive just fine being taken care of by mom.
Humans are monogamous because kids take so long to raise, but this is one aspect of family life where humans and pigeons differ radically. A pigeon can go from hatchling to fledgeling in about 2-3 weeks. Each clutch has 2 eggs, and usually both survive to adulthood. Pigeons usually have at least 4 clutches of eggs per year. So each pair can produce 2x4=8 more pigeons per year. If one pedestrian bridge had 5 support pillars, each with 3 nests per pillar, that bridge alone produces 120 pigeons per year. Considering how many bridges and parking garages Rosslyn has, it probably produces enough pigeons to populate much of norther Virginia.