What is an endangered species? It is a kind of plant or animal at risk of going extinct. Species become endangered for two main reasons. First, their habitat may disappear. The second way is if their population is too small.

Loss of Habitat

A loss of habitat can happen naturally. For example, nonavian dinosaurs lost their habitat about 65 million years ago. Scientists believe an asteroid hit Earth. It blasted dust into the air. Less sunlight reached plants, so they died. The air grew cooler. These changes killed off the nonavian dinosaurs, experts think.

Today, humans cause a lot of habitat loss. They cut down forests. They turn fields into farms. These changes affect wild species that live there. It may destroy the foods some animals need. There may not be safe places to raise young. Without a healthy habitat, some plants and animals may become endangered.

Loss of Genetic Variation

A population that is too small can also make a species endangered. How? Genetic variation. Genetic variations are small differences within a species. They help a species survive. Say one oak tree needs less water than another oak tree. If there is less rain, the first oak tree is more likely to live. It may give its genetic information to its seeds. Then that oak's seedlings may need less water, too.

The more genetic variation the better. It helps species survive habitat changes. It helps them survive diseases, too.

The Red List

One environmental group keeps a "Red List of Threatened Species." This list has seven levels. It tells which species are in the most trouble. Maybe the population is shrinking fast. Maybe its habitat is disappearing.

Here are the different levels.

Least Concern and Near Threatened

Least concern is one level. Species of least concern have little chance of dying out. This level includes people as well as dogs (Canis familiaris) and cats (Felis catus).

A near threatened species is one that may be in trouble soon. For instance, some violets are near threatened. These flowers grow in Africa and South America. Their forest habitat is disappearing.

Vulnerable, Endangered and Critically Endangered

These three levels include species facing bigger trouble.

Vulnerable Species: Ethiopian Banana Frog

This small frog lives in Africa. Its forest habitat is being cut down.

Critically Endangered Species: Bolivian Chinchilla Rat

This rat lives in South America. Its habitat continues to shrink. The big threat is the loss of its forest habitat.

Extinct in the Wild and Extinct

A species is extinct in the wild when it can no longer live in its natural home. An animal may still live in zoos, though. Or a plant may grow with special care.

Extinct: Cuban Macaw

The Cuban macaw (Ara tricolor) was a tropical parrot. They lived on the island of Cuba. People hunted them and made them pets. The last one died about 150 years ago.

Protecting Endangered Species

Why is it important to know if a species is endangered? If people know, they can take action. They can pass laws to stop hunting. They may stop people from destroying important habitats. Some species have survived because humans helped.

The brown pelican (Pelecanus occidentalis) is a good example. This seabird lives on the coasts of North and South America. In 1970, there were only 10,000 left. It was listed as vulnerable.

People took action. They raised baby pelicans and released them into the wild. They banned chemicals that harmed the birds. The number of brown pelicans climbed. Today, it is safe from extinction.