Generally, an endangered species is an organism in danger of disappearing from the face of the earth if its situation is not improved.
In the United States of America, the Endangered Species Act of 1973 was created to protect endangered species and the habitats on which they depend. This piece of legislation established two degrees of endangerment: immediate risk and threatened. For example, endangered species such as the California condor are at immediate risk of extinction and probably cannot survive without direct human intervention.
Threatened species, such as the gray wolf, are abundant in parts of their range but are declining in overall numbers and are at risk of extinction in the probable future. In addition to these official categories, biologists also recognize rare species, such as the greater prairie chicken, which exist throughout their range but in relatively low numbers.
The World Conservation Union (IUCN) is a nongovernmental organization collecting global information on endangered species. It has established similar categories of endangered species, but refer to them as critically endangered, endangered, and vulnerable.
The main causes of species extinction or endangerment are habitat destruction, commercial exploitation (such as plant collecting, hunting, and trade in animal parts), damage caused by non-native plants and animals introduced into an area, and pollution. Of these causes, direct habitat destruction endangers the most species. Many organisms have already been wiped out. The only certain thing is that we must act quickly. Once endangered species become extinct, they are gone FOREVER.