Two hundred years ago, only about 3 per cent of the world’s population lived in cities. Today, the figure is rapidly approaching 50 per cent even in previously rural countries, and the human population has increased nearly sevenfold. This phenomenal growth in urban living has transformed large areas of the planet.
It has created a wide range of artificial habitats – both in and out of doors — that animals can use as their homes, as well as vast amounts of waste that form the basis of animal food chains. As a result, there is a wealth of wildlife living with and among us.
For animals that can cope with disturbance, cities and towns can be good places to live. They have plenty of suitable places for sheltering or raising young, from trees and window ledges to underground passageways, and for omnivorous species they provide a constant supply of leftover food. In winter the artificial heat that escapes from buildings offers additional benefit. Even better, cities are relatively safe: cats and dogs aside, they are tree of many of the predators that animals would encounter in their natural homes, animals have adapted to urban expansion with different degrees of success.
Some species are never found in cities, always retreating as the concrete advances. Others, such as migrating birds and insects, are occasional visitors, touching down briefly before moving on. More adaptable animals — raccoons and red foxes. for example — are equally at home in town or country, and treat built—up areas as extensions of their natural habitat.
True urban specialists, such as the ubiquitous feral pigeon and the house sparrow are now so fully adapted to city living that they are rarely seen anywhere else. While feral pigeons can survive in the busiest city centers, many urban animals are found chiefly in parks and gardens — the small-scale versions of their habitats in the wild. These animals vary from one part of the world to another, but they include tree-dwelling mammals, such as squirrels and possums, and a wide range of birds.
The spread of suburbia is normally a threat to _ wildlife, but for these species it can actually be a help because it creates a patchwork of suitable habitats, sometimes with the bonus of food handouts.
In the natural world, many animals inadvertently create habitats for other species when they build their nests. Humans do exactly the same. However, because our “nests” are so extensive and complex, they can host an exceptionally wide range of animal life. Much of it is harmless, but some can cause problems or at least inconvenience.
Most indoor animals are small and nocturnal, which helps them to avoid being noticed by their human hosts. This is especially true of species that share daily living areas and that scavenge leftover food.
Silverfish, for example, emerge after dark to search for flour and other starchy produce, scuttling away if cupboards or drawers are suddenly opened, exposing them to the light. Cockroaches behave in a similar way but they are more of a nuisance because they spread disease. At dawn, nocturnal animals hide away, leaving the day shift to take over, houseflies, for example, are most active during the day because they navigate by sight, in basements and attics, wildlife is less attracted by the cycle of light and dark, and it is less frequently disturbed by human comings and goings.
For wild animals, attics resemble extra-large tree holes, while basements resemble caves. Wasps, birds, and house mice will all nest in attics — if they can get in — and they sometimes share this habitat with roosting bats. Basements and cellars provide a haven for spiders, which can survive for long periods without food and, in many cases, catch their prey in total darkness.
The advent of central heating has been an important factor in the increase in the number of animals that choose to share our homes. For example, cockroaches which were originally found mainly in warm parts of the world, are now widespread in cooler regions. Soft furnishings and carpeting also play a part: as well as helping to keep the home warm, they provide hiding places and nesting material for various animals.
LIFE IN URBAN AREAS
Animals have had millions of years to adapt to earth’s natural habitats, but only a fraction of that time to adjust to life in cities. Despite this, animals are never faraway in built-up places.
Their success is owed mainly to “preadaptation” — characteristics that evolved to suit one way of life, or habitat, but that accidentally turn out to be useful for another.
Thus, some animals thrive in man-made habitats that resemble the ones they would use in nature. Others succeed because they are highly adaptable and can exploit the opportunities that we inadvertently provide.
Some outdoor urban animals live on the same food that they eat in the wild, but for scavenging species — such as raccoons, foxes, and pigeons — the daily fare is often very different to that of their natural homes. These versatile creatures will try any kind of leftover food, however unfamiliar it looks and smells, and this highly opportunistic streak is the secret of their great success.
Modern food packaging can sometimes present problems, but they quickly learn how to tear or peck away at plastic and paper to get at the edible contents within, indoor animals get their food from one of 8 sources: the things we eat, the animals that eat those things, and the fabric of our homes,
The first category contains a wide range of household pests, such as rats, mice, houseflies, and cockroaches: the second category consists chiefly of spiders, but also centipedes and geckos in warm parts of the world. Spiders are almost perfectly adapted to indoor life, and although widely disliked, they make a positive contribution by keeping indoor insect numbers in check. Animals in the third category are the least welcome of these uninvited guests.
They include wood-eaters such as termites and beetles, as well as insects that attack other organic materials, such as wool. In many parts of the world these animals are serious pests.
LIGHT AND WARMTH
In cities, street lamps light up the night sky, while heat from buildings and traffic makes them far warmer than nearby countryside. Artificial lights confuse insect navigation systems and interfere with birds’ biological clocks.
As a result, songbirds sometimes sing late at night, and some species start building nests in winter, convinced by the bright light that it is spring.
Extra warmth is appreciated by a range of animals from butterflies to birds. In some regions, starlings commute into cities on winter afternoons to roost on buildings where they are relatively warm.
For birds and bats, the tops of buildings can make ideal homes. High above the ground and relatively undisturbed by people, animals feed and breed unmolested. Some species nest in attics or under eaves, while others favour the tops of chimneys.
Swifts, swallows, and martins are foremost among rooftop- dwellers and are prime examples of preadaptation at work: they naturally rest on cliffs or in crevices, but the rapid spread of towns and cities has provided alternatives that have enabled them to extend their range to places where they would otherwise be rare.