Feral Cities (33 page)

Temperature is not the only thing that makes the two cities a closer match than their locations would suggest. The residents of Phoenix and Baltimore have similar gardening tastes, so they opt for the kind of lawns that can be seen in almost every American suburb. The result? Phoenix and Baltimore share similar green spaces with similar plant species.

Water systems also bring cities into line with each other. To build Miami, wetlands were drained, while the development of Phoenix saw the construction of lakes and canals. Now, when it
comes to water, Miami and Phoenix are more like each other than the Everglades or Arizona desert.

The similarities between cities extend to fauna too. As we've seen, the animals that thrive in the urban world share common traits. The ability to keep a low profile is one, but urban animals also tend to be fast breeders with flexible behavior and diets. Just think of the stone martens of Berlin breeding faster than they can be killed, or the coyotes working out how to cross Chicago freeways or the red foxes learning to forage on Brighton Pier.

These animals are the garden weeds of the animal kingdom: adaptable, sneaky generalists that can overcome death by making lots of babies. This isn't just true of mammals. The most successful city birds are those with the most flexible behavior and an “I'll eat anything” attitude to life. Birds like pigeons and crows.

Size matters too. Larger animals like mountain lions, elk, and bears are more likely to be spotted and removed if they go too far into the city, while opossums and rats are small enough to slip past unnoticed. Bigger animals also have a harder time finding all the food they need in the city, and this principle applies as much at the level of tiny phorid flies as it does to cougars.

“The flies found in the center of the city tend to be small,” says Brian Brown, the phorid fly expert who heads the entomology department at the Natural History Museum of Los Angeles. “You expect that with mammals. You expect that there are going to be deer and bears in the mountains but downtown not so much, because there is a limited resource base available for them. But it's also the case in the tiny one-to-three-millimeter-long flies.”

Ecologists divide animals into two broad groups: K-selected and r-selected species. K-selected species are those whose numbers are limited by the amount of resources in the environment, animals like elephants and horses. In contrast, r-selected animals are limited by how much they can breed, and most of the successful urban animals fall into this group.

“The K-selected species are adapted to stable environments as it
takes a few years for them to get big, whereas things that are small don't grow as much and can reproduce more,” says Brian.

“The same principle operates at the level of small flies. So what we have living in downtown Los Angeles are fungus feeders largely and they are small species. The fungi they feed on are in the very perturbed environments like lawns and gardens that are constantly being disturbed, whereas the flies that live on gopher burrow and oak-associated fungi are going to be found in the mountains.”

Add to this our tendency to spread species like the European starling or spitting spider around the world, and the animal life of far apart cities becomes increasingly similar. More evidence is needed, especially from cities outside the most developed nations, but what already exists suggests that urban areas are a biome and, uniquely, one that is almost entirely manmade.

As Rob suggests, that raises an interesting question. Since we control, shape, and design the urban biome, can we mold cities into something that fosters the wildlife we want rather than just a gathering spot for animals that are sneaky, smart, and sex-crazed enough to make it their home?

It's an idea some people are already experimenting with.

It's an unexpectedly sunny October day in Chicago, a final hurrah of summer before the cold sets in, and Seth Magle is giving me a tour of the Nature Boardwalk at Lincoln Park Zoo.

The boardwalk's path snakes around the edge of a b-shaped pond within the grounds of the zoo. On either side of the path are clumps of tall, thin grasses and, among them, a smattering of delicate flowers. The calm water offers a clear reflection of the city skyline and, as we walk, we catch glimpses of the Lake Michigan shoreline that lies just across the road from the zoo.

“This used to be just a concrete-lined pond where they did paddle boats,” says Seth. “But then the zoo, some years ago, decided they wanted to renovate it as a native urban pond prairie ecosystem.
They reseeded the whole thing and threw out all the concrete. All of these plants are native Illinois prairie plants that attract certain arthropods and birds.”

As we pass under a small bridge that arches over the narrow of the pond, Seth points to the small ledges above us. “These are for cliff swallows,” he says.

Elsewhere along the path are strategically placed birdhouses. “Those are for black-capped chickadees because they are cavity nesting birds and we don't have a lot of cavities out here. We've built them in such a way that the aperture size excludes house sparrows but allows black-capped chickadees. That's been very successful.”

The pond also teems with life. Fish can be seen moving beneath the surface, and shiny dragonflies flit around near the bulrushes lining the water's edge.

At the southern end of the pond, there's a small island peppered with trees. “You'll probably see some turtles around the island,” says Seth. “We introduced painted turtles, but red-eared sliders and snapping turtles have found their way here on their own. We suspect that the red-eared sliders may have had help, since people buy them as pets and then let them go.”

One unexpected resident of the Nature Boardwalk is the black-crowned night heron, a stocky wetland bird with dark red eyes and black feathers that run from the top of its head and down the back of its otherwise white and gray body. These birds, which feed on fish and aquatic invertebrates, are an endangered species in Illinois, yet there is a thriving colony of them in Lincoln Park.

“The heron started showing up right around the same time as we renovated this area. We did have a small colony before that, but every year they are coming and nesting in larger and larger numbers right here in the heart of Chicago, which gives you an example of how you can conserve a rare species even in an urban landscape.”

The boardwalk is only the most visible example of Lincoln Park Zoo's urban wildlife work. As well as creating a slice of Illinois
prairie in the heart of Chicago, the zoo's Urban Wildlife Institute is busy piecing together the ecology of the city.

Seth is the institute's director, and his path into urban ecology was the result of sloth. “I feel like most people in wildlife studies have a very inspiring story of what got them started,” he says. “You know, they saw a bald eagle perched on a tree during a hike or they woke up and realized that the rattlesnake was their spirit animal or something. My own story is born out of laziness.

“When I was an undergraduate at the University of Colorado, we had to do a project where we had to watch an animal for a few hours and write down things about its behavior. Well, the apartment building I lived in in Boulder had a prairie dog colony living across the street. So I thought that would be perfect as I could virtually see them from my window and they were awake during the day and were not going anywhere.”

His professors were unimpressed with his plan to watch the tan-colored rodents. “I went to my academic advisor and said, ‘Hey, what's going on with all these urban prairie dogs that I see everywhere?' He said, ‘Oh, I don't know. Why would anyone want to know that?'”

Undeterred, Seth headed to the university library to check the scientific literature for information about the urban lives of black-tailed prairie dogs. There was nothing.

“I realized, ‘Wait, really? No one knows anything? These animals live fifty feet from where I sleep. How can no one know anything about them?' That just blew my mind. So I asked some very basic questions, the sort of things people were asking about animals in the wild in the early 1900s, and ended up turning that project into a masters thesis and then a PhD.”

Initially, Seth thought there would be little difference between the prairie dogs of urban Colorado and the wild, where the activities of these burrowing rodents changes the vegetation and soil in ways crucial for everything from sagebrush and burrowing owls to pronghorns. “I thought they would influence diversity in the same
way and that their populations would function the same, but that wasn't true at all. We found that they lived in ten times the density that they did in natural landscapes, that they didn't really migrate between colonies as much as they should, so their genetics were peeled back, and they didn't change the bird community in the same way as they did on the prairie.”

Seth's prairie dog study is ongoing, but now it is just one of the projects underway at the Urban Wildlife Institute, which has also been studying the effect of relocating groundhogs and nonlethal ways of keeping city rabbits under control.

The institute's flagship project is the biodiversity monitoring study. Its goal is to build as complete as possible a picture of wild Chicago. “We've set up over a hundred field stations. They initiate right over there in downtown Chicago and travel out west, southwest, and northwest,” says Seth, as we plant ourselves on a bench overlooking the boardwalk pond.

At each field station are motion cameras that take snaps of passing animals and alcohol-filled “pitfall” traps to catch spiders and insects. The team also holds regular bird counts at each station. As with the prairie dogs, the results have confounded expectations. “When I look back over my body of work so far, the recurrent thread is that things didn't turn out the way I thought they would,” says Seth. “Things were very different with the prairie dogs, and we're finding more or less the same thing here.

“One of the things we really expected to find in our data was that we would see fewer deer in sites where we see coyotes. Well, not true at all. The sites that have deer tended to also have coyotes.

“We think it's just that habitat is so limited and resources so limited that if you're a deer trying to decide where you are going to browse, you may have coyotes in your patch but leaving involves going across several roads and highways. It's a hazardous journey and it's uncertain if you will find another patch, and even then that patch may have coyotes too.”

This, he explains, is not how deer and coyotes behave in more
natural habitats. “We have this thing there called the ‘ecology of fear' where the deer move around and coyotes sort of track them. But that's not how it works in urban systems.”

Eventually the institute hopes to build a model for how urban ecosystems work that can explain how the wild residents of cities interact with one another, whether that's how coyotes and red foxes fight for territory or the influence of particular plant species on local birdlife.

That model is some way off, but Seth's hope is that by understanding these systems better, we can start using cities to protect species we value. “In the long term we want to have a thorough conservation strategy that can conserve all types of species,” he says. “To do that we need to learn to manage human-wildlife conflict in urban areas, so we can use these areas as part of our strategy for conserving species.”

The idea of using cities as places of conservation divides urban ecologists. “There is a schism between people who think all we can do is focus on managing the species that move into cities and the people who feel that we can use cities as an important component of conservation if we change the way we build our cities. I fall into the latter camp.

“I think that taking the view that cities are an evil, that anything that happens in the city is unimportant, is quite short-sighted, because I don't see any trends that we're going to stop urbanizing the world.”

Besides, he adds, we're running out of options. “Our rate of finding land to preserve is dwindling, so at some point we're not going to have any more preserves. But we will always have more city.”