Part 5 (1/2)

Partly because of this, and partly because humans have failed to think one step ahead of the rats, ”contemporary rat control seems to vary little from what was practiced in the Middle Ages,” said Hadidian. ”The usual consequence of killing rodents . . . is the return, shortly, to the population level that prevailed before, or one slightly higher.”

What we do know is that these rats are only in the city because humans are. Their omnipresence tells us about ourselves. Were we to be tidier, neither rats nor racc.o.o.ns would keep our company. Both are ”opportunistic omnivores”: they eat anything that is available. What good fortune for such an animal to find us humans, who provide in our trash and in our homes an omnivore's delight. Rats eat edibles-and they eat through lead pipes. They are happy with a small vertebrate meal or an afternoon's snack of nuts and fruits. Indeed, they are particularly interested in sweet, high-protein, and calorie-rich foods. Like us, they will even eat spicy food, after an initial, wise aversion to the stuff.

Conveniently, we even feed the rats outright. It is the city squirrels who are the intended recipients of the bounty handed out by urban animal-feeders. Every neighborhood has one or many individuals who take it upon themselves to regularly provide animals-especially squirrels and birds-with bits of bread, nuts, or seeds, tossing the bounty on the ground as they sit nearby, or spreading it Hansel-and-Gretel-like as they walk. But it is the rats, emerging after the squirrels and humans have denned up for the night, who ultimately reap the benefits of this human behavior.

As a result of their diet and our feeding, they live wherever we live. If you are reading this in a city, it is a good bet there is a rat living less than a quarter-mile from where you are sitting-not pa.s.sing through, not visiting: setting up a den and playing house. Studies of rats in Baltimore found that most rat activity is limited to a single city block or alleyway. As generations are born and move out of the family nest, rat ”neighborhoods” are formed, with an area the size of eleven city blocks containing many related rats. We have created the infrastructure that supports them beautifully. Grid layouts are particularly amenable to rat populations, as the rats use the grids to orient themselves. They can map their entire home range through its different smells: the area scrubbed with detergent, the trail left by people pa.s.sing with dogs, the area where the smokers stand by a building's side.

For the remainder of our walk, rodent boxes appeared repeatedly in my peripheral vision. I had never seen a rat in one, and I did not then. Rats are wary of new things-neophobic-which is at least partly responsible for their ability to elude the many and various attempts to bait and kill them: rats smell a rat in that big, black box. They will sample a new food first, before gulping enough to find it toxic. Later that very night, I spied a rat running to, sniffing, and then veering exactly around one. Given the rat's ability to learn to avoid foods from others' breath, this rat may have had an encounter with a less savvy rat earlier in the day.

We were again alone on the street, all the animals tucked away. While the subterranean landscape is a popular choice for the urban animal, the city also provides a commodious terrain above-ground. I asked Hadidian how the city we were walking through, New York, looked different to him than D.C. or Baltimore, where he monitors urban wildlife. He did not hesitate.

”Well, it's much higher. Everything in Was.h.i.+ngton is twelve stories or less because they don't want to overwhelm the monumental buildings. What you have here are functional cliffs.”

We both looked up.

As if demonstrating his point, a group of pigeons swooped down from its redbrick clifflike perch over Amsterdam Avenue. Just as it seemed they would nearly land on the cab of an eighteen-wheeler going uptown, they curled upward, then settled down and rounded the corner, out of view.

Biologists do not know exactly what the pigeons-or any birds-are doing on these great swooping flock dives. The birds may be in search of food, avoiding a real or imagined predator, or just stretching their wings. In any event, the ”flock-swoop,” as I think of it, is one of the magnificent natural sights of the city. And it is a sight that repeats itself daily, even hourly, in every sector of every city-in high-rent and low-rent districts, over empty lots and between skysc.r.a.pers. Even as I write this, my peripheral vision notices motion: out the great long windows of Columbia University's library the white of the sky highlights a flock of pigeons arcing gracefully south to land on the ledges above the windows.

This kind of bird flock behavior is commonly described in the academic literature as ”wheeling and turning,” though even to an amateur eye this hardly captures the dynamics of it. A group of thousands of European starlings is an ever-changing, amorphous splotch that pulses and throbs, ceaselessly erasing one shape and proposing another over it. Flocks of dozens of pigeons roller-coaster along invisible corridors ten to thirty feet above the street, and wend along and around a curvy, hilly highway we cannot see.

Biologists and others interested in emergent behavior-behavior of a group that is not under the control of any of its members-have identified a number of features common to all these flock-swoops. They are highly synchronized flight patterns that follow certain reliable rules. Individual birds often prompt the flock to take wing, but there is no leader once the flock is in flight. The flock-swooping can happen at any time, but it is more common at dusk or just before sunset, before the birds roost for the evening. Within the flock, the birds stay at least a wingspan apart from each other, though they pack more densely around the periphery than in the center of the group. The flocks themselves are much longer and wider than they are deep: the birds are spread, not layered. When the group maneuvers, it turns in what are called equal-radius paths. That is, if the flock turns left, it is not the result of each individual bird suddenly turning left. Instead, the birds at the front arc only slightly, and wind up being on the right side of the flock. Those birds at the left side wind up at the leading edge. When it is pigeons gliding, they keep a steep angle to the horizontal, which makes them more stable, especially in wind. No wonder they do so well along the breezy valleys of a skysc.r.a.pered city.

Watching the birds soar, pitch, and roll, and feeling happier just observing them, it occurred to me that one of the reasons that it is hard to pinpoint the function of this behavior may be that it is functionless. And the most cla.s.sic functionless behavior, seen in all mammals and most vertebrates, is play. Might these birds be soaring for the mere pleasure of it, a communal recess run to nowhere in particular?

Continue watching this bird play, and the paths that they travel almost start to become visible. When you imagine the city from the bird's vantage, it really does look like a series of canyons and cliffs. That notion of ”functional cliffs” intrigued me, and I pressed Hadidian on it.

”The whole business of cliff ecology is something you can start talking about when you get these structures,” he replied, motioning to a few buildings in the vicinity. ”Any building will have what we can call 'wind shadows': little places where the wind doesn't hit. It certainly doesn't scour, the way it does on most structures or surfaces.” The result is that although buildings look like hostile, lifeless zones, the face of a wall can support a whole ecosystem. Natural cliffs, too, have their own microhabitats and microclimates, and they support a huge amount of specialized flora and fauna.

The textbook cliff is a tall, steep rock face, with a flat top and maybe a bit of overhanging rock on the top edge. In other words, almost precisely the shape of the cla.s.sic apartment building, with a vertical face and an eyebrow of cornice at the top. On a natural cliff, there are ten million places for life to bloom. Algae lives on the surface, small plants root in crevices between stones, multiple horizontal ledges collect debris and things that grow in debris-and this then attracts all the animals, invertebrate to vertebrate, that feed on these plants. Similarly, on a building, plenty of opportunistic, specialized plants live in porous stone, in cavities between stones or in broken stone, and at the intersection of brick and marble, or stone and steel. And on the top of the cliff may well be a raptor, perched on a ledge or nesting in a nook.

. . . Or under an air-conditioning unit. Falcons, hawks, and even eagles are again a common sight in the urban sky. They build their aeries in cathedral bell towers; on bridge towers; on, famously, an ornamental stonework ledge on a Fifth Avenue apartment building. Indeed, the animals, plants, and ecology of buildings-man-made cliffs-show ”striking similarities” with those of natural cliffs. Cliff animals include mice, various squirrels, the aforementioned raptors, racc.o.o.ns, porcupines . . . stop me if these sound familiar. Coyotes have been seen to feed and reproduce in cliff sites-and coyotes are among the most recent urban settler. We do not see many cliff-using black bears, lynx, or mountain goats in the city. Well, not yet.

Indeed, some ecologists have even proposed an ”urban cliff hypothesis”: that the urban rats, mice, bats, pigeons, and plants that are so familiar to us evolved from ancient cliff-dwelling rats, mice, bats, pigeons, and plants. Hominid fossils from h.o.m.o erectus onward have been found in caves at the base of cliffs. As our ancestors moved from caves and rock shelters to shelters of wood, steel, and stone, the animals may have simply moved with us. Humans still live in ”concrete and gla.s.s versions of their ancestral cliffs, caves, and talus slopes,” Doug Larson, a promoter of this theory, writes. The unlikely habitat of the cliff supported species that had to adapt to their unusual conditions. This adaptiveness turned profitable as the species followed humans, and were flexible enough to dine on our food and live in and on our structures.

The evidence for this hypothesis is multifarious. Pigeons, for example, are well adapted to perch on cliffs or building ledges, as their takeoffs are terrific, explosive affairs, as anyone whose step disturbs a flock of grazing pigeons knows. Their wing muscles are very strong, allowing them to hover and take off nearly vertically, helicopter-like. Rodent remains have been found in cave dwellings dating back tens to hundreds of thousands of years ago. Even the bedbug probably evolved from caves and rocky outcroppings in Africa and Asia, where the nasty things fed on pigeons and bats who lived there; the German c.o.c.kroach, that ubiquitous city bug, can still be found on the toe of rocky slopes in Africa, where it feeds on fallen cliff detritus. One could even make the case that we build the structures we do in order to reproduce clifflike dwellings. Often our buildings have lots of ”subs.p.a.ces,” which replicate ledges and crevices. We grow plants and trees on terraces-since plant species may thrive in small cliff juttings. We prefer to have our front doors set back and slightly elevated from ground level-just as an entrance to a cliff cave would be. And around us in these urban cliffs is exactly the biodiversity that we look for in nature.

As we rounded the final corner on our walk, a group of loafing pigeons, startled by a pa.s.sing bike, lofted upward. Until that moment I had not realized what was so odd about our urban-wildlife tour. In part, it had held more traces of wildlife than actual wildlife. But more than that, even those animals we saw were remarkably quiet. Mute, even: any sounds made by birds in flight were largely lost among the sounds of the city. When these pigeons took off, though, we heard their wings slapping the air and their bodies. Until then, they were silent-movie stars, padding along not twenty feet from us in complete silence. Pigeons are typically far from silent. Males coo as they woo, generating a large round warm noise while they puff their chests, spread their tail feathers, and try to look mate-worthy. When eating, pigeons hammer their beaks against the ground, messily spraying food around them. Their long nails sc.r.a.pe the ground audibly as they walk. But our pigeons stepped lightly, cooed psychically, and m.u.f.fled their pecking. And we had only to look around us to see other stars of this spontaneous silent film: above our heads, dried and curled leaves noiselessly rustled on a towering oak; to our right, apparently weightless squirrels leapt from a stone wall to a tree trunk. All make sound, and all were close enough to be heard, but we were not bothered by not hearing them.

And just as in silent films, without sound the scene we saw was suspended in time, the action having no clear beginning or clear end. I watched a dog across the street venture forward, unhurried, noiseless. It felt like a little peek at infinity.

I asked Hadidian if he had any predictions about what the next animal to move into the big cities might be.

He smiled and was silent for a minute. When he spoke, he began slowly, almost cautiously, then quickly built into an outpouring of tumbling sentences.

”The real question is what animals will truly come to adapt to cities and accept the urban environment for the opportunities it presents, and it certainly does present a lot of opportunities-food, shelter . . . I'm sure you know about the phenomenon called the Heat Island effect?” (I did not.)5 Hadidian continued all the same. ”So an animal could subsist in a more northerly lat.i.tude than the species might usually be found.” Thus we see the mockingbird, a warmth-loving bird, in the Northeast; the beaver and Canada geese are, as we all know, so well adapted to human presence that they are considered ”problems.”

”I guess it depends on the city. I mean, twenty years ago people didn't think that javelina would be colonizing Tucson, Arizona.”

”What is that?”

”A peccary? The wild pig.”

”They are in Tucson?”

”Yeah.”

”Seriously?”

”Yeah.”

”On the street?”

”Well not by day, but yes. They're in backyards. They come to water.” Wild pigs, in search of a good drink in the desert, have lived in Tucson, a city of half a million people, for twenty years. In some cities of Germany, wild boar-feral hogs-are common sights on the streets. A wild boar in New York City would surprise me, I have got to admit.

”Wouldn't coyotes have surprised you?” Hadidian reminded me of New York's alarmed, overblown reaction to the arrival of a handful of coyotes, Canis latrans, in the city parks over the last few years. Some Chicagoans are surprised to learn that there is a well-established group of coyotes living in the city proper. Night dwellers, the animals may grow up, mate, reproduce, and die unseen by the human nine-to-fivers. ”It's eye-opening to realize. They shelter in, like, shrubs by the post office.” Hadidian pointed to a few bushes packed into a small s.p.a.ce beside the sidewalk. ”You could have a coyote (nesting) in a place like this. People would walk by all day long, never look, never see it.”

I hung back behind Hadidian to take a closer look. No coyote. As far as I could tell.

When I grew up in the foothills of Colorado, canids around our house were not so surprising. But then again, in my early childhood we never saw elk, a five-hundred-pound animal which is now common enough in Boulder that the animal has its own street signs. The city of Bristol, England, has foxes like we have stray cats. When Hadidian began studying urban wildlife twenty-five years ago, even deer were not around.

My question was unanswered. Maybe there is no profit in predicting the next urban animal. Maybe we just have to wait for it, and keep an eye out. But if you are interested in hurrying up the process, take a cue from Hadidian's racc.o.o.n tale. Plant a persimmon tree in your city and see what shows up.

1 Lotor is Latin for ”washer,” alluding to their habit of dipping food in water before eating.

2 It is not a crazy crash of screeches, flas.h.i.+ng lights, and possibly predatory or confrontational creatures approaching me: it is a subway car approaching the station.

3 When I have played this video in my psychology cla.s.ses, students feel confident of their final numbers, but most of them count incorrectly, a phenomenon I cannot explain as expectation's responsibility.

4 This is true for monkeys who have been tested in this game, too. And they respond faster than humans in every trial.

5 I have since learned: the mean temperature of a city with a million residents can be up to 5.4 degrees warmer than the suburb outside the city-up to 22 degrees warmer on some evenings.

”We must always say what we see,

but above all and more difficult, we must always see what we see.”

(Le Corbusier).