Introduction to Urban Wildlife
In October 1994, visitors at Woodlawn Cemetery in the Bronx, one of New York City's five boroughs, spotted what appeared to be a large, mangy dog prowling among the headstones. The animal proved to be a coyote. By early 1995, people had spotted several other coyotes near the cemetery, some—traffic victims—dead in the street.
Most New Yorkers were surprised to learn that there were wild animals living in their midst. But it really wasn't so unusual. Despite their reputation as wilderness creatures, coyotes have become common in cities and suburbs across North America. And they have lots of company. Black bears are regular visitors to backyards in densely populated suburbs of cities in New York, New Jersey, and Colorado. Peregrine falcons swoop from high-rise buildings in Baltimore, Chicago, and Los Angeles. And deer and wild turkeys find food on the grounds of the White House in Washington, D.C.
Although wildlife has existed in urban communities since the first cities were built, most people are amazed to learn how extensive and varied the populations of wild animals have become in American cities. The growing presence of wild animals among us testifies to their intelligence and adaptability to the human environment.
Parks, backyards, cemeteries, and golf courses are among the places wild animals have chosen to call home. Central Park, surrounded by tall apartment buildings in the heart of New York City, has nearly 300 bird species. Less obvious places where wildlife has taken up residence are grassy parkway medians, railroad rights of way, and flood-control channels. And few people would consider concrete ledges, window sills, air vents, chimneys, and storm sewers as suitable habitats, but many urban species find that such places are similar to the sites in a natural landscape where they might have established dens or nests.
For Urban Animals, Cities Imitate Nature
Like animals in the wild, urban creatures require habitats that will satisfy their need for food and water, a place to rest and sleep, cover for rearing young, and protection from predators. Wildlife ecologist Larry W. VanDruff of the State University of New York's College of Environmental Science and Forestry in Syracuse has found that metropolitan areas contain three categories of habitat. He describes them as the central city core, the mainly residential suburbs radiating out from the core, and, farthest out, a fringe area that is relatively free of development. VanDruff emphasizes that these zones have no sharply defined borders. The landscape changes gradually from the built-up inner city out to the outlying areas where farm fields and forests prevail.
All three habitat areas provide rich food resources. In addition to finding their natural foods, animals can supplement their diet with pickings from a variety of sources, ranging from garbage cans to garbage dumps and landfills. Metropolitan areas have plenty of water as well, in reservoirs, park lakes, birdbaths, fountains, gutters, and reflecting pools. In fact, the food and water resources of urban communities offer animals a greater variety of habitats than was available there prior to human habitation.
Cities also alter the local climate. Heat produced by houses, apartment and office buildings, factories, and automobiles makes the city warmer than outlying areas. Suburbs are cooler than the central city core, but even there, heat generated by homes and automobiles makes them significantly warmer than wild places. The warmth of these so-called microclimates improves the survival rate of many urban species.
Urban animals share several common characteristics. First, they are adaptable. As their natural habitat disappeared, they changed their behavior to fit the new conditions of the urban environment. Second, urban species tend to be opportunists and omnivores—that is, they are willing to eat a variety of foods, both animal and plant. In addition, they are intelligent, some extremely so. And finally, urban species have adjusted to the presence of people. They have learned to recognize which kinds of human behavior pose a threat and which do not.
The Rat
Some urban animals live in such close proximity to people that they share food, a characteristic biologists call commensal behavior. The common rat (also called the Norway or brown rat) heads the list of commensal species. From their homes in basements, sewers, and trash piles, they go after anything people eat. Rats rarely starve.
For as long as history has been recorded, rats have lived in cities. Biologists believe these animals originated in the wilds of northern China. They stowed away on ships traveling from Asia to Europe in the Middle Ages and hitchhiked to the Americas with European colonists. Burrowers by nature, rats can gnaw through brick, concrete, wood, and metal, and they can squeeze through small spaces. Female rats breed all year long, except during periods of severely cold weather, producing litters of six in less than a month. In a year's time, a female and her offspring can produce 1,500 rats. Dogs, large cats, and human exterminators kill some of them, but no natural predator has evolved in cities to control the rat population. The best defense is to keep alleys and basements clean.
Starlings, Sparrows, and Pigeons
Like rats, three bird species introduced to America—starlings, house sparrows, and pigeons—soared in number because they encountered no natural predators or parasites and an abundance of resources in their new home. Central-city-core animals outnumber wildlife in the suburban and fringe habitats because of the huge numbers of these three species in the central areas. However, the suburbs and fringe areas support a greater diversity of species.
House sparrows and starlings originated in Eurasia and northern Africa and lived in European cities for centuries before coming to America. The sparrow (also called the English sparrow) arrived in the United States in 1852, when a sparrow fancier released 50 of the birds in a Brooklyn, New York, cemetery. They thrived on the grain used to feed draft horses. When automobiles replaced horses, sparrows dwindled somewhat, but soon the birds switched to trash bins and bird feeders for food, and their numbers once again soared. Researchers estimate the current U.S. sparrow population at more than 140 million.
Starlings got their start in America in 1890 and 1891, when a misguided philanthropist released about 100 in New York's Central Park. Starlings eat almost anything, from seeds and insects to garbage. They like to nest in holes, and they find abundant nesting sites beneath the roofs of buildings and in air vents. They also take over bird houses intended for more desirable species.
Extremely aggressive, starlings drive off native birds and sometimes destroy the other birds' eggs or kill their chicks. Scientists have found that the U.S. starling population has soared to nearly 1 billion. Pigeons are another introduced species that flock all over American cities. Pigeons are descended from rock doves, a Middle Eastern wild species that moved into cities thousands of years ago. European colonists brought domesticated pigeons to America for food, to use as messengers, and to keep as decorative pets. Many subsequently escaped from captivity, and some were released. With their year-round breeding habits, these liberated pigeons quickly soared to millions.
City pigeons have learned that trash baskets afford easy pickings, and they are so tolerant of people that they will eat handheld birdseed, popcorn, and stale bread. Rock doves roost and nest on tall cliffs and rocky ledges, so their domestic descendants are right at home on window ledges, eaves, lofts, and under window air conditioners. They deposit large amounts of droppings on buildings, streets, and sidewalks. In addition to being a nuisance and expensive to clean up, the droppings may also accelerate erosion of stone and concrete in buildings.
The Peregrine Falcon
Since the 1970's, federal and state wildlife agencies have been releasing peregrine falcons in urban areas to help restore the species after it had been decimated by pesticide poisoning. Peregrines naturally nest on cliffs and mountain ledges, so they were preadapted for city living. One of their favorite foods is pigeon. A peregrine will hurtle from its perch on a high-rise ledge or bridge tower at speeds sometimes exceeding 320 kilometers (200 miles) per hour. It kills its prey on the wing, and returns to the nest to feed. In terms of pigeon control, peregrine reintroduction had only modest success because the falcons fiercely defend territories of up to 8 kilometers (5 miles) around their nests. Thus, even the largest cities have space for only a few pairs of falcons—hardly enough to make a serious dent in the local pigeon population. Nevertheless, the program has boosted the peregrine population, and they now swoop around major cities all over North America.
Many bird species native to America have embraced cityscapes as readily as introduced species. One example is the nighthawk. An insect eater, the nighthawk has learned that the city's heat creates rising columns of air that send hordes of insects spiraling upward. Emitting a nasally "peent" that sounds like an electronic pager, it dives and swerves to catch insects on the wing on dark summer nights. The species also has adapted its nesting behavior to city life. Whereas in the wild, nighthawks nest on the ground in open fields, city birds nest on flat rooftops, which provide security from predators.
Bold Squirrels, Clever Raccoons
Probably the most commonly seen animal in cities is the squirrel. Squirrels abound in parks from the central city core to the fringe.They also nest in buildings when they find a suitable niche high off the ground. The gray squirrel is the most numerous species. It is native to the eastern half of the United States from Canada to Florida. Red squirrels and fox squirrels predominate elsewhere, though they may overlap with the gray. Flying squirrels are also common in cities and suburbs, but being nocturnal (active at night), people rarely see them.
Gray squirrels moved into urban communities early in the 1900's, as logging cleared large areas of hardwood forest. These squirrels find everything they need where a few tall trees stand. They build nests of twigs and leaves in forked branches, and in winter they curl up in tree hollows. Trees also provide them with acorns, nuts, and bark to eat. But gray squirrels also help themselves at bird feeders, and whenever they can find them, they eat bird eggs and even chicks.
The main difference between the squirrels' native and adopted habitat is people. Although forest squirrels are extremely shy, those in the city have learned to be quite bold, coming close to people and begging for food. Begging helps urban squirrels survive, but junk-food handouts and fights at bird feeders make their fur scruffy-looking.
Raccoons are among the most prevalent and interesting of the small, furry animals populating the urban landscape. With highly sensitive forepaws that rival the human hand for dexterity, raccoons can open garbage cans with tightly fitting lids and even unlatch doors. In the 1980's, John Hadidian, an urban-wildlife biologist with the National Park Service, spent four years tracking 30 radio-collared raccoons in Washington, D.C. He found that the animals ate anything they got their paws on. About the only thing they would not eat is raw onions.
Hadidian also learned that city raccoons are unusually sociable. Several of the ones he studied lived in the same tree. And the animals clearly did not feel threatened by people. Nearly a fourth of the raccoons established dens in and around houses, though they avoided homes with dogs.
Recent Arrivals to the Urban Scene
Compared with squirrels and raccoons, the beaver is a relative latecomer to populated areas. But the beaver population has been surging in the 1990's, mainly in fringe and suburban habitats. Fairly typical is the situation across central Maine. There, beavers are gnawing down trees and damming streams in residential suburbs and occasionally even in downtown Augusta, the state capital. The beaver population explosion in Maine stems from two causes, according to biologist Gene Dumont of the state's Department of Inland Fisheries and Wildlife. First, from the 1930's onward, many farmers abandoned the land, and their farms reverted to forests crisscrossed by streams—the perfect habitat for beavers. Then, in the 1980's, the demand for beaver pelts in the clothing industry started to decline, pelt prices dropped, and the number of trappers fell by half. By 1996, Maine's beavers numbered in the tens of thousands.
Known as the engineers of the animal kingdom, beavers build dams to create ponds, and within the ponds they erect cone-shaped lodges out of logs, stones, and mud where they live and raise their young. But beavers do not restrict their dam-building to streams in forests. Beavers have found it far easier to plug a drainage culvert 1 meter (3 feet) wide under a road than to build a dam 90 meters (100 yards) wide across a stream. Water backs up behind the plugged drains, flooding the landscape and washing out roads.
Wildlife officials have tried relocating beavers, but the animals return or others move in. Moreover, once caught and released, a beaver learns to avoid traps. A new strategy calls for clearing the debris from a culvert, fencing it off, and building a half-moon-shaped structure of metal posts and fencing upstream from the drain. Once the beavers build their dam against the barrier, officials insert drainage pipes to allow water to flow through the dam to the drain.
The Coyote
Another relative newcomer to the urban habitat is the eastern coyote. It commonly roams the suburbs of cities in the East and the upper Midwest. Scott Smith, a state wildlife biologist, has studied coyotes living in the northern suburbs of New York City. He has found they are not only adaptable to people but are also lazy, eating whatever is easy to get, from garbage and grasshoppers to pet food and even pet cats. They have thrived where farmlands reverted to forest.
The eastern and western coyote are subspecies. In the early 1900's, the western species began to migrate eastward across Canada, eventually dispersing through the Northeastern United States and as far south as Florida. Genetic evidence indicates that eastern coyotes interbred with wolves, evolving into a larger animal than its western counterpart. Easterners average 16 to 18 kilograms (35 to 40 pounds), but they can reach 23 kilograms (50 pounds) or more, whereas westerners average 11 to 14 kilograms (25 to 30 pounds).
Western coyotes became suburbanites earlier than their eastern cousins. They had moved into the suburbs of Denver, Los Angeles, San Diego, and other Western cities by the 1960's, possibly earlier. The westerners are even less wary of people. Residents of the suburbs around Los Angeles, for instance, regularly see coyotes trotting down neighborhood streets, drinking at lawn sprinklers, and eating from dog dishes. Coyotes occasionally attack small dogs, but according to Scott Smith, such confrontations stem from the coyotes' territorial instincts, not because the dog represents food.
Surging Populations of Canada Geese and Deer
Some wildlife species have become urban dwellers mainly through human interference with their natural behavior. Such is the case with flocks of Canada geese that nest in suburban areas of the United States and stay put year round instead of migrating to Canada, as they normally would. This behavior change can be traced to the 1930's. Up to that time, hunters who shot wild geese and sold them to food stores kept large flocks of geese to use as decoys. They clipped the birds' primary flight feathers to prevent them from flying off and tethered them by lakes and ponds to lure migrating birds within shooting range.
But in 1935, the U.S. Congress outlawed live decoys, and within a few years, thousands of semidomesticated geese were turned loose. They joined flocks of captive-bred geese that federal and state game agencies had released on ponds for public enjoyment. By the 1950's, large flocks of nesting geese were spreading throughout the Northern states. Once they select a breeding site, they are faithful to it. Thus, within several generations, the geese lost whatever migratory instinct they still had. Today, young birds in these flocks travel only a few kilometers from their birth nests to set up breeding sites with lifelong mates. Coyotes and foxes sometimes kill nesting geese but not in sufficient numbers to slow their population growth.
Deer are not far behind geese in overrunning American suburbs. White-tailed deer range everywhere in the United States and Canada except parts of the Southwest. Mule deer dominate from the Rocky Mountains to the Pacific Coast. When settlers arrived in North America, the two species had an estimated population of 50 million. Because of land-clearing and intense hunting, white-tails numbered only about 500,000 by 1900, and mule deer even fewer. But by 1996, populations had risen to more than 15 million white-tails and about 6 million mule deer.
The major reason for their resurgence is a lack of natural predators—mainly wolves, which were virtually exterminated in the early 1900's, and a decrease in hunting. In the mid-1990's, several states launched programs to increase deer hunting, but cars probably "harvest" more deer than hunters do. Deer like the forest edge, and suburban environments mimic this habitat. They relish nibbling on fruit trees and many other popular plants in the suburban landscape. And they consider the produce in suburbanites' vegetable gardens gourmet fare. They quickly learn to avoid feeding when dogs and people are around to harass them.
Cougars In the West
The abundance of deer is at least partially responsible for the arrival of cougars in many large Western cities. At least 100 sightings of cougars—also called pumas or mountain lions—occur every year in the Denver metropolitan area, according to Todd Malmsbury of the Colorado Division of Wildlife. Residents of other Colorado cities, including Boulder, Colorado Springs, Fort Collins, and Pueblo, also report seeing cougars. The cities lie along the eastern edge of a string of peaks known as the Front Range of the Rocky Mountains.
Development around all the cities has pushed deeper into the foothills of the Front Range. The big cats rarely attack people, but they often kill pet dogs and cats for food. Even dogs as large and strong as Doberman pinschers and German shepherds are easy prey for cougars.
In the 1940's and 1950's, both cougars and deer were uncommon in the foothills of the Rockies. But since then, Colorado's wildlife management practices have protected the land and animals, turning the area into prime mule deer habitat. And Malmsbury credits the booming deer population for attracting the lions.
Some scientists have additional explanations. For example, wildlife biologist Allen E. Anderson, now retired from Colorado's Division of Wildlife, thinks the cougars around Colorado cities are mostly young animals seeking their own space. During 14 years of research, Anderson found that the cats are extremely territorial, defending home ranges that for males can extend for a radius of more than 160 kilometers (100 miles), slightly less for females. His studies showed that after being weaned and driven off by their mothers, young cats may travel up to 325 kilometers (200 miles) before finding a place to settle where they will not be killed as "trespassers" by resident cougars. Anderson also found that the ideal habitat for cougars has forests, canyons, and gullies—features common to Colorado's Front Range.
Suburban Sprawl Squeezes California's Cougars
In contrast to Colorado's wandering cougars, those sighted in California around Los Angeles, Sacramento, and San Diego appear to be established residents. The increased frequency of cougar sightings may be due to creeping urban sprawl that brings people into established mountain lion habitat in unprecedented numbers. The state also banned cougar hunting in 1972, allowing the population to increase. With no threat from hunting, the cats no longer seem to fear people. They regularly turn up in backyards to prey on pets or other animals.
Suburban Orange County, southeast of Los Angeles, is fairly typical. There, residential developments have crept out from Mission Viejo, San Juan Capistrano, and other towns into the foothills of the Santa Ana Mountains. The canyons, forests, and chaparral (dense growth of thorny shrubs or small trees) of the foothills are home to deer and elk as well as the cougars that prey on them. A study found that this habitat supports over half the lions in the region even though the foothills are included in only about a third of the animals' home ranges.
Wolves and Bears In the East
Cities in the East and Midwest are also getting their share of large predators. The eastern timber wolf, a species that goes out of its way to avoid human contact, has moved into the upper Midwest. Driven nearly to extinction in the region in the early 1900's, the wolves began returning to Minnesota, Wisconsin, and Michigan in the mid-1970's. Since then, the population has ballooned. Minnesota wolves now number about 2,200, nearly double the number of the first census in 1978.
Biologist Michael Doncarlos of Minnesota's Department of Natural Resources said the wolf's protected status under federal and state laws was at least partially responsible for the animal's resurgence. Protection led to an explosion of the wolf population in Minnesota's northern wilderness areas, forcing some wolves southward in search of territory and food. Wolves now occupy the urban fringe and suburban areas only 90 kilometers (56 miles) from Minneapolis and St. Paul, an area of more than 2.5 million people. Doncarlos believes the wolves will continue to expand their range because their prey, white-tail deer, are at record high numbers throughout the Great Lakes region.
The largest animal moving into America's urban habitats is the black bear. Remarkably, people in New Jersey, the nation's most densely populated state, are sighting bears in the Highlands, which border on the state's most crowded section. This region, roughly 64 kilometers (40 miles) from midtown Manhattan in New York City, has evergreen forests, lakes, and swamps mixed with residential communities. Nearly every day, residents of West Milford and other towns in the Highlands report bears wandering through their backyards.
In the early 1970's, New Jersey's annual bear count varied from 10 to 30 animals. By 1996, the count was up to more than 400. State wildlife biologist Patty McConnell believes two major events triggered the rise. First, in the 1960's, the U.S. Army Corps of Engineers bought up thousands of hectares of farmland along the Delaware River for a dam project, but the project was canceled and the land reverted to forest. And second, neighboring Pennsylvania prohibited bear hunting for several years in the late 1970's. The rise in the number of bears forced younger bears to cross the Delaware and seek new territory in New Jersey's reforested areas. By 1996, bear habitat was pushing against lakeside communities, and bears were attracted to easy-to-get food.
Searching For Harmony
Officials are turning to science for ways to control the numbers of undesirable animals in urban habitats. Biologists' major advice is to not leave out anything edible that will attract large animals. People may like to watch deer forage in their backyard, but not the coyotes, bears, or mountain lions that may follow close behind.
On the other hand, some steps are being taken to enhance the urban habitat for desirable species less adaptable to people. Some biologists are collaborating with developers on designs that will preserve woodlands, meadows, and other natural elements of the area. Some communities have left corridors linking large habitats to accommodate seasonal wildlife movements or built tunnels under roads at known crossings to reduce the number of animals killed by vehicles. Most urban dwellers delight in watching animals and birds and applaud such efforts to promote a harmonious relationship between people and wildlife.