Species Adapted to Urban Life

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Some species manage to adapt to urbanization even though their habitat is gone. Three different modes of adaptation allow some species to do quite well amid dense human populations. First, structural adaptive traits enable an animal to hide from predators. During London’s industrial revolution of the 1800s, as an example, resident peppered moths darkened from their normal light gray color so they could hide on soot-covered tree bark. This new coloring represented a structural adaptive trait. Second, species inherit physiological adaptive traits, for instance, black bears that invade campgrounds. Their digestion has adapted to table scraps and fast-food leftovers, not at all the food they have evolved to eat! Third, behavioral adaptive traits are changes in an animal’s lifestyle to accommodate humans that have encroached into their environment. Raptors such as hawks, falcons, and ospreys have adapted to building nests on the sides of skyscrapers, under bridges, and atop light poles, and they fledge several new families each season.

In all cases in which species have adapted to urban life, the animals have done so because their genetic makeup enabled them to include one or more of the three adaptive traits: structural, physiological, or behavioral. Almost every animal that has adapted to urban life, furthermore, lives as a generalist rather than a specialist: rats, mice, raccoons, coyotes (now living in New York City’s Central Park!), and many birds such as crows, starlings, house finches, and house sparrows.

Adaptation plays a critical part in species survival because animals have only three ways to respond to a change in their environment: adapt to the new conditions through natural selection, migrate to another area, or go extinct. The species most likely to go extinct are those that either cannot adapt quickly to changes brought by urbanization or cannot migrate to a new, safer place. Even migrating animals sometimes find natural migration routes blocked by human activities and are then left only with urban wildlife protected areas such as preserves.

Aldo Leopold observed as early as 1933 the capacity of animals to adapt to human incursion into their habitat: “Lewis and Clarke found elk, deer, grizzly bear, and mountain sheep on the flat plains of Nebraska, a country very different from the mountain forests with which we now associate these species.” Fortunately for the species noted by these naturalists, the animals had been given enough time over generations to learn how to find food and live at a different altitude than the Great Plains. Urbanization now occurs so fast, perhaps only human-made migration corridors can aid wildlife.