Our planet is teeming with life. Tigers and turtles, bats and bees, gnats and gnus, crabs and crabgrass—the list seems endless. We've named more than 1.5 million species, and suspect that millions more remain undiscovered. Scientists call this mind-boggling variety of life biodiversity. With so many species, it's surprising to realize that so many are in danger of becoming extinct.
Extinct species are plants and animals that once lived on Earth, but no longer live anywhere in the world. Endangered species are most in danger of extinction. Even large populations of animals can be at risk. Passenger pigeons once flew in flocks so large that they darkened America's skies. Over time, habitat destruction and hunting lessened the birds' numbers. The last one died alone in the Cincinnati Zoo in 1914.
Dinosaurs, dodo birds, and passenger pigeons are all extinct. Extinctions have always happened naturally, but in modern times, people have pushed wildlife to
Endangered species are animals and plants that are in danger of becoming extinct. The U.S. Endangered Species Act of 1973 was passed to protect threatened wildlife and habitats so they don't go the way of the dodo.
Why do animals become endangered or extinct? The main reason is loss of habitat. Habitat destruction or fragmentation (the breaking up of natural habitat areas into progressively smaller patches) can make it tough for wildlife to survive. However, as people learn to take better care of plants, animals, and their habitats, endangered and threatened species may begin to make a comeback. In fact, bald eagles, black-footed ferrets, and many other species already have.