The American alligator was taken off the endangered species list on June 4, 1987. The only other species of alligator on Earth is the Chinese alligator. (Photo: Thomas & Pat Leeson/Photo Researchers, Inc.)

Since the Pilgrims washed ashore along the Massachusetts coast nearly 400 years ago, more than 500 species have become extinct in the United States.

Three decades ago, Congress passed the Endangered Species Act of 1973 (ESA) to conserve the ecosystems upon which endangered and threatened species depend. Thanks to the ESA, dozens of species are still present today that otherwise might not be. Yet the endangered species list remains crowded. Only a handful of the 389 animals have been removed from the list in the past three decades.

Here are some examples:

AMERICAN ALLIGATOR
Listed as endangered: March 11, 1967
Taken off the list: June 4, 1987

• The only other species of alligator on Earth is the Chinese alligator.
• Adult males typically weigh between 400 to 500 pounds.
• The alligator is the official state reptile of Florida.
• Because they replace worn-down teeth, alligators can go though 2,000 to 3,000 teeth over the course of a lifetime.

Habitat
American alligators live in wetlands, freshwater lakes, ponds, and rivers in the Southeastern United States.

Why was it endangered?
Alligators were hunted for their hides.

How did it make its comeback?
After the American alligator was listed as endangered, the U.S. Fish & Wildlife Service prohibited the trade of alligator hides. Today, the trade of alligator hides and meat is regulated by the states.

New York City is one of the favorite habitats of the American peregrine falcon. (Photo: U.S. Fish and Wildlife Services)

AMERICAN PEREGRINE FALCON
Listed as endangered: June 2, 1970
Taken off the list: August 25, 1999

Peregrine falcons can dive at speeds of more than 200 miles per hour.

Their wingspan is nearly four feet.

New York City is one of their favorite habitats.

Pairs of falcons often return to the same nesting spot year after year.

When peregrine falcons are courting, they put on an impressive aerial acrobatic performance.

Habitat
Peregrine falcons nest on cliffs, bridges, and urban buildings across the U.S.

Why was it endangered?
The peregrine falcon population was threatened by use of the pesticide DDT. A toxic chemical, DDT caused the falcons to lay thin-shelled eggs. As a result, the eggs cracked before chicks could hatch.

How did it make its comeback?
The Environmental Protection Agency made it illegal to use DDT. Peregrine falcons were also bred in captivity, and their chicks were released into the wild.

The population of the Aleutian Canada goose has grown from just 800 birds in the mid-1970s to nearly 40,000 today. (Photo: U.S. Fish and Wildlife Department/AP Wide World )

ALEUTIAN CANADA GOOSE
Listed as endangered: March 11, 1967
Taken off the list: March 20, 2001

The Aleutian Canada goose winters in California.

While adults largely feast on plants, goslings, or young geese, survive on a diet of insects, such as ground beetles.

Adults weigh just four to six pounds.

The population has grown from just 800 birds in the mid-1970s to nearly 40,000 today.

Habitat
These birds nest in the Aleutian Islands, a chain of islands that stretches west from the tip of the Alaskan Peninsula.

Why was it endangered?
Foxes were first introduced onto the islands by people interested in establishing fur trade in the mid-1700s. The foxes preyed on the geese.

How did it make its comeback?
The foxes were removed from the islands.

The brown pelican was taken off the endangered species list in 1985. (Photo: Arthur Morris/Corbis )

BROWN PELICAN (recovered along U.S. Atlantic Coast)
Listed as endangered: October 13, 1970
Taken off the list: February 4, 1985

The wingspan of a brown pelican is more than seven feet.

Brown pelicans survive on a diet of fish.

They can dive from great heights—up to 60 feet—into water to snatch fish.

The pelican's pouch, located under its bill, can carry three times more than its stomach.

Pelicans fly in single-file formation.

Habitat
Brown pelicans live in the coastal areas in the Eastern and Western U.S.

Why was it endangered?
Contamination by pesticides, including DDT and endrin, interfered with their breeding.

How did it make its comeback?
DDT was banned, and the use of endrin was curtailed.

Gray whales spend the summer in Alaska and winter in Baja California. (Photo: George D. Lepp/Corbis )

GRAY WHALE
Listed as endangered: June 2, 1970
Taken off the list: June 16, 1994

Gray whales spend the summer in Alaska and winter in Baja California.

The calves, or babies, weigh 1,100 to 1,500 pounds and measure roughly 15 feet at birth.

Gray whales are covered with orange whale lice and white barnacles.

A gray whale can stay submerged under water for up to 15 minutes.

Habitat
Gray whales migrate up and down the coast of the Pacific Ocean.

Why endangered?
They are hunted for whale bone, blubber, and other body parts.

How did it make its comeback?
Hunting was prohibited in the early 20th century. Over time, the gray whale population has slowly recovered.