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Welcome to Subirdia

Sharing Our Neighborhoods with Wrens, Robins, Woodpeckers, and Other Wildlife

Yale UNIVERSITY PRESS

Home Turf

With the disappearance of the forest, all is changed.

—George Perkins Marsh, Man and Nature (1864)

Who? Who? Whoo? The annual interrogation started at 3 a.m. on a cold January morning. I was used to the interruption and, from the comfort of my bed, listened intently for any response. In the distance I heard a soft reply: Hoo! Hoo! Hooo! I would have preferred the harmony of two singers rather than the long-distance debate that was just beginning. This conversation—a typical territorial encounter between the two male great horned owls that divvy up my neighborhood—was going to last for a while. These owls, each of which stands nearly two feet tall, get an early start on spring by reasserting their property boundaries and courting in the heart of winter. As far as scientists know, they spend their entire adult lives in the same area, with their lifelong mates. If the male in my yard is able to keep the neighboring owls away, then his partner might spruce up the old crow nest, high in the fir trees, and lay a clutch of two white eggs. She would then incubate the eggs for a month and brood the young owlets. As long as their efforts succeed, both members of the pair would hunt the neighborhood for mice, squirrels, and other small animals to feed their growing offspring, who won't begin to fly from the nest until they are nearly two months old. As the parents work to usher in the next generation, my woods will quiet. The busy parents will softly hiss, meow, and coo, often composing duets. But then the real noise begins, for fledgling owls screech like frightened children all night long.

As much as I tire of night screams of young owls, I was thrilled to learn that two pairs of predators as formidable as great horned owls could find enough food and shelter to live among my family and our neighbors. Their presence would directly benefit our garden by keeping the nonnative eastern cottontail rabbits on edge. What was more, I knew that the owls were only one of many top predators that kept an eye on the streets and yards where I lived. As the owls hunted the night, Cooper's hawks, red-tailed hawks, and bald eagles hunted the day. There were smaller owls as well—saw-whet and screech—that hunted mice and large moths. Some predators that hunted here in the past were gone. At least at the moment there are no pumas, grizzlies, or wolves. But coyotes, black bears, and bobcats have all put in appearances. And this is my yard, not the wilderness!

My home provides shelter for more than a pair of large and powerful owls. The forested back acre I own provides a canopy, native groundcover, and brush piles adequate for two pairs of Pacific wrens and a pair each of spotted towhees, Pacific-slope flycatchers, and western tanagers. Three species of salamanders and two species of frogs seek shelter in the duff and deadwood that enriches my soil. Garter snakes hunt these amphibians and the slugs that are famously abundant in our cool, wet climate. The trees that live and die here house and feed a nice assortment of woodpeckers, chickadees, creepers, swallows, bats, and nuthatches. Fringing shrubs supplement my bird feeders with native berries, nectar, nuts, and bugs for busy grosbeaks, thrushes, juncos, and sparrows. The more I look and listen, the more my yard reveals. Though a key financial investment and a personal haven for my family and me, this property is much more than a mere commodity. As Aldo Leopold, the father of wildlife science, articulated so eloquently, my land is a community.

* * *

On a recent airplane flight I saw cities and their suburbs from a wider perspective. As we climbed out of Kansas City, Missouri, skyscrapers towered above the eastern deciduous forest. Below me the forest had been tamed, but not demolished. Dense stringers of trees connected seamlessly with city parks, streets, and subdivisions to outline big, lazy rivers. I saw an urban forest as a green quilt that sheltered two million people from the city's cold concrete and steel.

As we continued west, I could feel the exhaustion in the land below me. In contrast to the urban forest, the mosaic of land I viewed had been forced to conform to our mechanized world. Square ponds, rectangular fields, and crop circles defined this part of Earth. Massive irrigation projects held back and tamed the greatest of western rivers. Our replumbing of these aquifers endangers fish but enables crops to flourish where they could not naturally. The energy that once carved great canyons now energizes a power grid that cuts at right angles across the landscape and converges on cities and farms. Prairie and sagebrush have been pulled, scraped, and burned from the arid lands of western Kansas, Nebraska, and eastern Washington. Dark soils were fully plowed, planted, and starting to develop a ragged beard of green. These actions have made refugees of our native grouse, larks, sparrows, and buntings.

The depression I felt from seeing wall-to-wall agriculture eased as we met the jumble of western mountains. A lightly falling snow added mystery to a wild landscape. Most valleys were farmed or settled. And I could see where patches of timber had been downed and fossil fuels exploited. But there was also a huge expanse of wilderness that allowed me to dream. As we passed over Yellowstone Lake, I forgot about people and wondered what the wolves were doing. I took comfort in knowing that below me many of the animals that avoid subdivisions and farms have some space.

My flight from Kansas City to Seattle reflected national and global trends. Throughout western Europe, eastern North America, and much of Asia our cities and suburbs dominate the land, literally lighting the night sky. But worldwide, less than 1 percent of Earth's soil surface is covered by urban development. In the United States this statistic is a bit higher—3 percent to 4 percent of the nation is a city, town, or village. The reach of cities is much greater. In 2010, one-quarter of the conterminous United States was designated as "metropolitan," because these areas held a city of at least fifty thousand people. Another 20 percent were deemed "micropolitan" on account of their economic and social connections to cities of between ten thousand and fifty thousand people. Our proximity to cities gentrifies nearly half of the U.S. national land base with well-tended lawns and gardens, public parks and recreation areas, and the infrastructure of transportation, communication, and energy. Worldwide, our coasts are densely settled, but even here, tree cover can be substantial. Currently, one-quarter to one-third of most urban regions around the world are covered with a canopy of trees or other natural greenery. Metropolitan areas in the United States contain an estimated seventy-five billion trees that shade a third of the area. These "lungs of the city," which produce oxygen and clean our air while providing essential habitat for other species, will be at risk in the future.

Agricultural lands fill in around our settlements and carpet much of eastern Europe, midwestern North America, Central America, and South America. One-third of Earth's land, and a full 40 percent of the United States, is farmed—far more than we occupy with our villages, towns, and cities. Parts of Africa, Australia, South America, and the Arctic remain wild and sparsely settled. Antarctica is a wilderness, but today this is the exception.

Most demographers expect our growing population to lead to more cities, especially moderately sized ones, widely distributed across the planet. In the United States, a million more acres become urban each year. As Harvard ecologist Richard Forman puts it, an urban tsunami is on the horizon. For many, the flood has already hit and the swimming is tough; one-third of all urban residents live in slums. When did this vast urbanization happen?

* * *

Five to six thousand years ago our ancestors in Mesopotamia and Syria created the world's first cities. As early populations rose and fell with environmental change, war, and disease, early agrarian settlements ebbed and flowed. At first, the majority of people lived outside of these creations, but as civilizations grew, so did the propensity of citizens to leave the dangers of the country for the comforts of the city. Large settlements took shape about three thousand years ago. Babylon, for example, in what is now Iraq, sheltered two hundred thousand. Between one thousand and two thousand years ago large cities were rare and centered in rich agricultural regions such as the Nile and Yangtze River valleys (Nanjing, China, may have been home to one million residents) and the Basin of Mexico (two hundred thousand lived in Tenochtitlán-Tlatelolco). Metropolises that we would recognize today are more recent inventions; three centuries ago only Constantinople, Edo (the former name of Tokyo), Peking, London, and Paris housed more than five hundred thousand people, and only thirty-four cites were home to more than one hundred thousand. The lure of cities proved irresistible, so appealing in fact that in 2008, for the first time in our history, more of us lived in cities than outside of them. Each year seventy-two million more people flock to cities. By 2050 more than two-thirds of all humans are expected to live in cities.

The city itself is only a part of the urban niche we have constructed. Like a galaxy, moderately large cities spin off suburbs, small edge cities, and a distant fringe of settlement called "exurbia"—"a semirural area beyond suburbia yet within its shadow." This gradient of urbanization from a densely populated urban core to a lightly peopled exurban fringe is dependent economically and socially on the commerce and culture of the city. The human census acknowledges this connection as it classifies Earth's residents. In the United States, for example, if we live in a city (areas with more than one thousand people per square mile) or in the associated less dense areas (at least five hundred people per square mile) connected to these cities, we are called "urban." In the 2010 census, as a resident of exurban Seattle, I became one of the urban people because the population density in my neighborhood crept over the lower critical threshold. Although my neighbors and I live on an average of two acres each—one hundred times more land than the residents average in the world's most densely settled city, Dhaka, Bangladesh—we are all urbanites. Our urban niche now includes commercial, industrial, and residential lands as well as their interstices of protected reserves, green recreational areas, and waterways.

It staggers me to contemplate the implications of our new lifestyle. We now live predominantly in a niche that was unknown only six thousand years ago! Generations of city people no longer have the interest to live in the country and may truly struggle to survive doing so. The social customs, diet, climate, modes of communication, and transportation in the city would be as foreign to our ancient ancestors as theirs would be to us. We have evolved into a new ecological role with cultural barriers to our rural legacy. Evolutionary biologists might consider us well along the process called "anagenesis"—the evolution of a new species from its ancestors that results from the gradual accumulation of isolating differences over time. Certainly we are already culturally distinct from our ancestors, but most biologists would not consider this adequate to proclaim that we are truly a species apart from ancestral Homo sapiens. They would require more lasting distinctions that make our DNA incompatible with that of our ancestors.

I have no doubt that our new niche and culture are, in fact, promoting genetic changes. As we prefer mates with new physical or cultural features, challenge our brains with the demands of new technologies, expose our metabolic processes to new diets, and succumb to new mortality agents, we expose our populations to new selective pressures that are capable of causing genetic, evolutionary change. Old foes such as dim eyesight, dull hearing, disease, and physical deformities no longer doom us to a short life with a reduced chance of reproduction. In their place are new hazards of urban life: fatty foods, carcinogens, inactivity, automobiles, and stress. And therefore, it is only a matter of time (and I doubt very much time) before our new lifestyle leads to speciation. Thus far, only about 250 generations of humans have been exposed to the rigors of urban life—an icing on the cake of our evolutionary history, as eminent evolutionary biologist Jerry Coyne points out. But I contend that this icing is an influential force significantly distinct from our earlier 300,000 generations of hunting and gathering that is able to shift our evolutionary trajectory. The day is near when we are no longer Homo sapiens (wise person) but instead something entirely new. Perhaps we are already Homo urbanus (city person).

As urban people we live in a time when everything changes rapidly. Gone is the Holocene, the geologic period that succeeded the Pleistocene, or ice age, twelve thousand years ago. Then, the climate was stable and life changed slowly. We now live in the Anthropocene—a period of chaotic change initiated by humans several millennia ago. Our fellow creatures quickly adapt, evolve, or die out. Like the great ice sheets that covered much of Earth during the Pleistocene, concrete and lawn now creep from our cities into the deep recesses of nature. How will these changes affect the community of life to which we are ultimately linked? Listening to the owls and others that live among us, we might hear the answer.

Finding Subirdia

In visiting vast, primitive, far-off woods one naturally expects to find something rare and precious, or something entirely new, but it commonly happens that one is disappointed.... The birds for the most part prefer the vicinity of settlements and clearings, and it was at such places that I saw the greatest number and variety.

—John Burroughs, Wake-Robin (1871)

I'm not really a city person. I spent my formative years in small towns and faraway places in Kansas, Montana, Arizona, and Maine. As a research biologist, I spend a lot of time in the woods watching birds, not people. So when in 1997 I took a job in Seattle, Washington, I was quickly out of my element. My family settled outside the city, where trees cushion the view and neighborhoods include extensive natural greenways. But as I commuted to the city each day, I was struck by the extreme ways we engineer cities and how this engineering alters fundamental ecological processes. Just consider water. In a forest, rain is intercepted by leaves or soaks into the ground as it slowly carries important nutrients downhill to lakes, rivers, and the sea. When buildings and pavement replace forest, rain rushes to rivers in flash floods loaded with sediment and pollutants. When it suits our needs, we pump the river uphill or force it to flow, piped and underground, out of the sun's nurturing rays.

No wonder many of my colleagues consider cities unmitigated ecological disasters. Not only do we push around urban rivers, but we also construct buildings that funnel winds through urban canyons and foster industrial enterprises that heat the land. We are so noisy birds can't hear one another. Paving what was paradise removes and fractures habitat that other species absolutely require. Traditional ecologists have shown us the power we wield and the danger it poses to many other organisms on Earth. Hit songs such as "Big Yellow Taxi" by Joni Mitchell and "The Last Resort" by the Eagles have popularized the notion.

I see these changes and feel their effects every day as I ride a bus from the exurbs to the city. I shed my coat as I enter the urban heat island, pass through planted woodlands of trees from around the world, and cross a bridge that spans a ditch dug to connect the once-inland Lake Washington to the Pacific Ocean. But I also encounter a rich diversity of birds. Majestic bald eagles hunt from streetlamps. Once-endangered peregrine falcons nest under steel bridges or atop skyscrapers. Cormorants decorate the cottonwood trees as they strike a silent pose to dry outspread wings in infrequent sun breaks. Crows, gulls, and pigeons dine on our leftovers. Parties of bushtits, flocks of robins, and mixed groups of nuthatches, chickadees, and kinglets enliven the shrubs and lawns on which I walk. A paradox eats at my subconscious. Everything I have learned as a conservation biologist tells me cities are bad for biodiversity—the sum total of life in an area—yet the feathered collective I encounter seems wholly unconvinced.

Maybe my problem is that I live in Seattle. After all, this "Emerald City" nestled in wild country is young. European settlement did not begin until 1851, and even today buildings are interspersed among trees, rivers, lakes, and the Puget Sound of the Pacific Ocean. Forests of towering native Douglas-fir, western hemlock, western red cedar, red alder, big- leaf maple, and black cottonwood mix with street trees to provide a green canopy over nearly one-quarter of the city. The forests of Seattle and its suburbs now embrace 141 species of trees, including 30 native species and ornamentals from North and South America, Europe, Asia, and Africa. Some are problematic invaders, but in total they provide a diverse menu of foods and nesting and roosting sites for birds. Birds flock to my green city. Surely they must shun the concrete elsewhere.

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Excerpted from Welcome to Subirdia by John M. Marzluff, Jack DeLap. Copyright © 2014 John M. Marzluff. Excerpted by permission of Yale UNIVERSITY PRESS.
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