Sharing the Planet: Can Humans and Nature Coexist? - effects of urban growth

USA Today (Society for the Advancement of Education), Jan, 1999 by John Tuxill, Christopher Bright

An equally disturbing trend is population declines in more widespread species, particularly those that migrate seasonally between breeding and wintering grounds. Long-term population declines are tied to a host of contributing hazards. Habitat loss squeezes species on both breeding and wintering grounds, as well as at key stopping points--such as rich tidal estuaries for shorebirds--along their migratory routes. In North America, the loss of almost half of all wetlands has been a major factor behind a 30% drop in the populations of the continent's 10 most abundant duck species.

Exposure to chemical pollution is another hazard many birds face. The greatest risk of pesticide and pollution exposure occurs in developing countries, where many chemicals banned from use in industrial nations continue to be applied or discharged indiscriminately.

The decline of migratory birds is sobering because it is a loss not just of individual species, but of an entire ecological phenomenon. Present-day migrants must negotiate their way across thousands of miles of tattered and frayed ecological landscapes. The fact that many birds continue to make this journey, despite the threats and obstacles, is cause for hope and inspiration. Yet, as long as bird diversity and numbers continue to spiral downward, there can be no rest in the effort to protect and restore breeding grounds, wintering areas, and key refueling sites that all birds--migratory and resident--can not live without.

Mammals' dark future

About 25% of all mammal species are treading a path that, if followed unchecked, is likely to end in their disappearance from Earth. Out of almost 4,400 mammal species, about 11% already are endangered. Another 14% remain vulnerable to extinction, including the Siberian musk deer, whose populations in Russia have fallen 70% during this decade due to increased hunting to feed the booming trade in musk, used in perfumes and traditional Asian medicine. An additional 14% of mammal species tend to have larger population sizes or be relatively widespread, but nonetheless face pressures that have them on the fast track to threatened status in the not-too-distant future.

Among major mammalian groups, nearly half of primate species (lemurs, monkeys, and apes) are threatened with extinction. Also under severe pressure are hoofed mammals (deer, antelope, horses, rhinos, camels, and pigs), with 37% threatened; insectivores (shrews, hedgehogs, and moles), with 36%; and marsupials (opossums, wallabies, and wombats) and cetaceans (whales and porpoises), at 33% each. In slightly better shape are bats and camivores (dogs, cats, weasels, bears, raccoons, hyenas, and mongooses), at 26% apiece. Rodents are the least-threatened mammalian group, at 17%, and the most diverse.

The biggest culprit in the loss of mammalian diversity in the late 20th century is the same as that for birds--habitat loss and degradation. As humankind converts forests, grasslands, riverways, wetlands, and deserts for intensive agriculture, tree plantations, industrial development, and transportation networks, many mammals are relegated to precarious existences in fragmented, remnant habitat patches that are mere ecological shadows of their former selves.