Slogan for cesium
Around the world, nature is moving to the cities. “Ecological novelty pervades the urban environment, ” says Michael Perring of the University of Western Australia. Gardens and cemeteries, abandoned industrial areas, transport corridors, and even suburban trash cans are all grist to nature’s mill. Sometimes cities provide specialist habitat. Buildings and bridges in cities from Budapest and Florence to Brussels and New York provide substitute cliff roosting sites for birds of prey such as peregrine falcons (Falco peregrinus). For a decade now, I have enjoyed watching the fastest birds of prey in Europe swooping on city pigeons from their nests in the turrets at Chichester Cathedral on the southern coast of England. They seem to like it as well as their “proper” sea-cliff habitat.
More often, cities are irresistible food sources. Australia’s once rare gray-headed flying foxes found so much food in Melbourne that a colony of thirty thousand of the bats has formed there in the past two decades. Raccoons (Procyon lotor) are joining others who forsake the rural life for city scavenging. They are smart enough to negotiate any American urban obstacle course in search of a meal. They are “able to squeeze into locked garages, open secured garbage cans, unzip tents, and pry up lids on Tupperware, ” wrote one blogger after watching a PBS documentary. Mile for mile, there are five times as many raccoons in American suburbs as in the surrounding countryside.
Oddly, many species find cities safer than the countryside. The coyote (Canis latrans) lived mainly in the southwestern United States until the twentieth century but then headed for the cities. In the absence of hunting, their survival and reproduction rates are higher there. There may now be two thousand coyotes living in the suburbs of Chicago, navigating the city’s highways by night with rarely a mishap. Los Angeles, New York, and Boston also have substantial populations. They will eat rabbits, rats, and even household pets. Ecologists say they are the new top predators on the mean streets and have adapted to their new territories by living more densely, with smaller home patches, and becoming increasingly nocturnal. Once known as the ghosts of the plains, they are now increasingly the ghosts of the cities. Like foxes in the United Kingdom, they are in part fleeing human foes in the countryside. But while British foxes no longer fear showing themselves, coyotes keep to dark places and go out mostly at night, “quietly conquering urban America, ” as the Economist put it. Golden-headed lion tamarins, squirrel-sized monkeys, came out of the disappearing coastal forests of Brazil and found a new home in the suburbs of Rio de Janeiro. That, as James Barilla of the University of South Carolina points out, makes them both endangered and invasive.
Many species that traditionally get on well with humans have become convinced urbanites. The house sparrow (Passer domesticus) seems to have been with us at least since we started farming. Rarely found anywhere remotely wild, it sticks with humans, their landscapes and buildings. The relationship has served the bird well. It is probably the most common bird in the world. Only the chicken comes close. A flock lived for several years inside Heathrow Airport’s old Terminal 2, feeding off crumbs from the snack bars. Sparrows will even join us underground. Yorkshire coal miners at Frickley Colliery found a nest two thousand feet down at the bottom of a shaft in the mid-1970s. The birds stayed for three years.
In recent years, sparrows have been in decline in some of their favorite urban environments, with numbers halving in Britain since the 1970s and similar declines in the United States. Nobody is sure why. Theories range from unleaded gasoline and mobile phones to our urban tidiness. But the fact that, after thousands of years, they seem to be finding us uncongenial is worrying.
There are few such fears for the wild boar (Sus scrofa). It is another old friend that has certainly not lost its love of human habitat. We domesticated it nine thousand years ago. Since then it has ranged the Old World, from Japan to Britain, and Indonesia to the Atlas Mountains of Morocco. It has often been our calling card. The Polynesians took it to Hawaii, the Spanish to Florida, and the English to New England and Australia, where some twenty million now roam free. The United States has some six million of them. The wild boar is not a fussy companion. It will roll around in mud or dig up golf courses. It will sweat it out in Texas or the Borneo rain forest but produce its own steam in the forests of Siberia. It will eat kitchen scraps, mushrooms, snails, turtle eggs, live birds, or rotting carcasses.
Such Homo sapiens– loving species adapt to city dwelling in interesting ways. Gray squirrels get more aggressive and daring. Many birds sing louder and move up the scale, singing higher notes that are less likely to be drowned out by the rumble of city traffic. Pigeons make what appear to be regular planned journeys on the London Underground, saving their wings and energy as they commute to get to food supplies or return to their nests.