The vast numbers of animals that once covered the earth have rapidly disappeared as the human population has increased. When all the individuals of one kind of organism are gone, the species is extinct. Extinction is irreversible. We call an organism endangered if we think it is headed for extinction as a result of our actions.

Some plants and animals are more likely to become endangered than others: those that people consider dangerous, those that compete with us for resources, or those that have something that we value. An animal can easily become endangered if it lives only in a very specialized habitat or in a small area such as an island, or if it feeds on only one type of food.

From the gathering of exotic birds for the pet and feather trade to the sometimes adverse effects of development and industry, we continually threaten the welfare of birds. Habitat destruction, introduction of exotic plants and animals, contaminants, hunting, gill nets, the pet trade, and human-caused catastrophes such as oil spills, have taken their toll.

People love to keep birds as pets because of their bright colors and songs. The illegal capture and export of many tropical birds for the pet trade has harmed wild populations. Many kinds of birds are easily bred in captivity. Before you buy a pet bird, find out where it came from.

Oil spills kill thousands of seabirds. The birds are poisoned when they swallow oil while trying to clean their feathers. The oil also destroys the water-repelling quality of feathers that keeps the birds warm and dry - many birds become waterlogged and drown.

Our appetite for land to expand our activities has forever changed the face of the planet. When people change the habitat where an animal lives, they take away its food and shelter. Unless the animal can survive with the changes or find another home, it will die.

Large numbers of birds fall pray to domestic cats and other pets. The American Bird Conservatory estimates that over three million birds are killed by cats that roam outside each year. Even after adpting to a new environment, birds still have many other dangers to answer to.

Toxic chemical levels continue to pollute our water, soils, and atmosphere. Most of these contaminants are products of our industrialized society or our efforts to poison agricultural pests. Birds are very sensitive to such toxic materials; their population declines should alert us to environmental problems that may affect our own quality of life.

The pesticide DDT produces DDE which affects an enzyme that controls eggshell formation in birds. Prior to banning the domestic use of DDT in 1972, the eggshells of heavily-contaminated birds such as Brown Pelicans, Ospreys, Peregrine Falcons, and Bald Eagles were so thin that they broke when the adults sat on the eggs to incubate them. DDT continues to be used extensively in other countries.

Bird populations are especially vulnerable on islands, where they have been decimated by cats, rats, and goats brought by people. Many of these isolated island birds show no fear and are easy prey because they evolved in the absence of land enemies.

Throughout the world, many species of birds are in danger of becoming extinct. In North America, the California Condor, Whooping Crane, Eskimo Curlew, and Kirtland's Warbler are represented by only a handful of individuals. Six bird species have gone extinct in North America within the last 150 years: the Passenger Pigeon, Great Auk, Labrador Duck, Carolina Parakeet, Bachman's Warbler, and Ivory-billed Woodpecker. In each case the species was driven to extinction by over hunting, habitat loss, or a combination of these two factors. During the last 300 years, the world has lost at least 80 species of birds. Probably many more went extinct before they were identified.

The most important way to ensure survival of birds and other animals is to protect undisturbed areas of their natural habitat.

Classroom Activities: Bird for Sale Oil Spill