Nine species of birds nest in my neighborhood. Three are the usual urban aliens: pigeon, starling, and house sparrow. A fourth is the semialien house finch, a bird native to the western U.S. that entered Chicago from the east after being accidentally introduced onto Long Island 50 years ago. The other five are native birds: common nighthawk, chimney swift, mourning dove, American robin, and northern cardinal.

All nine of these could be starters on an all-city bird team. They are species that have figured out how to make a living in the heart of the modern American metropolis. The American crow qualifies as the tenth starter on that team, but this year crows are not nesting in my neighborhood. The remains of a bulky nest in a tree at Winthrop and Rosemont suggests that they were here in 1994.

I live in a very urban situation. The 40 acres of my neighborhood– bounded by Broadway on the west, Granville on the south, and Sheridan on the north and east– include only eight single-family houses, and just two of these are occupied by single families; the rest have been divided into apartments.

We have light industry in the form of a tool-and-die shop and an assortment of retail establishments, including a McDonald’s and Vee-Vee’s African restaurant. We have Hamilton’s, the bar that has been serving Loyola students for more than 60 years, the Ismaili Center, Sacred Heart Schools, and a residence of the Sisters of Charity of the Blessed Virgin Mary.

Mostly, we have apartments– lots of four-story buildings, some dating from the 20s and some four-plus-ones built circa 1970. A dozen buildings reach eight stories or more, and the neighborhood’s tallest building is 17 floors. Thousands of people live on these 40 acres.

The buildings are also home to six of the nine species of wild birds. Chimney swifts, as the name suggests, build their nests in chimneys. In the days before chimneys appeared in North America they nested in hollow trees. Their legs, absolutely useless for walking or hopping, are excellent for clinging to vertical surfaces.

Their nests are fashioned of sticks glued to the chimney wall with a sticky saliva produced by the females. There’s a swift in southern Asia that builds its nest entirely of this saliva, which is what bird’s nest soup is made of.

Chimney swifts gather in large colonies in suitable chimneys. All of the swifts in our neighborhood– and there must be close to 200– nest in a single chimney in an apartment building on Granville. The older buildings in the neighborhood have chimneys that once served to vent incinerators that burned the buildings’ garbage. We now dump our garbage in landfills, so the swifts can move in without fear of asphyxiation.

The swifts coming home in the evening is our neighborhood’s most impressive wildlife display. A cloud of them whirl in rapid circles over the chimney, 200 throats combining their twittering calls into a wall of sound. And then about half an hour after sunset they begin to drop into the chimney. At first just a few birds drop each time the flock passes over. But then more and more, until suddenly there is no more sound and no more movement. The birds are gone until tomorrow.

Now the nighthawks come out. Like the swifts, they live by catching insects in flight. By day they sit on the gravel-and-tar surfaces of flat roofs, where they lay their two eggs and rear their young. By night they swoop and flutter over the city. You can detect them by their calls, blatting noises like a cross between a door buzzer and a whoopee cushion.

My guess is that we have five or six birds hunting over the neighborhood. The city must produce lots of flying insects to support populations of swifts and nighthawks that could number more than 1,000 per square mile.

Pigeons, starlings, house sparrows, and house finches also use buildings as nest sites, and they are all extraordinarily resourceful in recognizing good nest locations. They build under overhanging eaves, in stone scrolls that decorate the tops of windows, under the stone sills at the bottoms of windows, in any crack or crevasse poor maintenance creates. Half a block south of me house sparrows have built nests in the narrow space between the walls of two four-plus-ones. No more than three inches separate the walls, and the birds have to coast in with their wings folded. But six or eight pairs have found a home there.

Starlings like air conditioners. The four-plus-ones have window air conditioners set in their walls. Protective screens are supposed to cover them, but many have fallen off. So the birds build in the space under the compressor.

Ivy is great for both house sparrows and house finches. In fact, all three of the house-finch nests I have located are hidden in ivy on apartment-house walls.

The remaining three of my nine neighborhood birds have managed to squeeze into the tiny bits of green space between buildings. We have one vacant lot that has grown into a tangle of shrubs and small trees. As it happens, this lot is right across the street from a formal garden in the rear of the residence of the Sisters of Charity. The combined seminatural landscape of the two places provides a home for one of our three pairs of nesting robins.

The rest of our neighborhood green space consists of the yards of the remaining single-family houses, the landscaped front yard of our apartment building–where one of our two pairs of cardinals has built a nest–the parkways, and the narrow strips of green between the sidewalks and the fronts of buildings.

One of our three pairs of mourning doves already has a fledgling out of the nest. Another has been sitting on eggs for two weeks in a nest at Rosemont and Sheridan.

My neighborhood is typical of urban ecosystems. We have a few species that are mostly dependent on people to provide them with nest sites and a few others adaptable enough to slip into the tiny seminatural spaces we leave between buildings, but that’s about it.

By way of comparison, I looked at my results from a 40-acre piece of Somme Woods, the Cook County forest preserve where I helped conduct a nesting survey three years ago. The 40-acre patch I selected has an oak grove, a bit of wetland, a small piece of prairie, and a shrubby meadow. It is a type of landscape that was once common in northeastern Illinois. Thirty-two species of birds, almost four times as many as in my neighborhood, nested in that patch in 1992.

However, my neighborhood has more individuals than Somme Woods. We counted a total of 105 nesting pairs of those 32 species at Somme. I can’t make a precise count of the superabundant species in my neighborhood, but even leaving out the chimney swifts, I’m sure we have more than the 210 individuals it would take to make 105 nesting pairs of all species.

Again, this is typical of urban ecosystems. We have created a remarkably uniform habitat, so any animal that can live in that habitat can become very abundant. In natural circumstances habitats are both more varied and more finely divided between species, so we get lots of species and modest populations. This tendency reaches its apogee in tropical rain forests, where there are thousands of species and nearly all of them are rare.

For at least the past 600 million years, since the appearance of multicellular life in the Cambrian period, the tendency has been for ecosystems to evolve in the direction of complexity. Massive extinctions have from time to time wiped out substantial percentages of existing species. But after each extinction new species evolved. Ecosystems redeveloped, proceeding from the harsh simplicity imposed by mass extinction to a complexity based on finely drawn divisions of the resources of the environment.

Ecosystems seem to want to be complex. As our actions reduce more and more of the earth to the sort of depauperate condition exemplified by my neighborhood, we are leaving less and less space for life to function as it has functioned for the past 600 million years. No one can predict the consequences of our activities, and that is something we should be thinking about during our endless arguing over the Endangered Species Act. Being conservative, in this case, means being willing to take strong action to avoid doing anything irreversibly stupid.