Mammals—a group that include humans—are warm-blooded animals with hair and vertebrates, or backbones. Unlike other classes of animals, female mammals produce milk to nourish their young. Almost all mammals give birth to live young (except for the platypus and echidna, which lay eggs).

Scientists have identified more than 5,400 mammal species on Earth, roughly one-fifth of which are known to be threatened or extinct. One of the most threatened order of mammals is the primate, which includes monkeys and apes. The United States has more than 400 mammal species. Of those mammals, nearly a quarter are listed on the U.S. endangered species list for reasons including habitat loss, climate change, pollution, and disease.

Bat Image


Nocturnal, flying mammals that eat fruits and insects

Bats Indiana Bat
Jamaican Fruit-Eating Bat Little Brown Bat
Flying Squirrel


Gnawing mammals with a single pair of incisors

American Beaver Black-Tailed Prairie Dog
Dusky-Footed Woodrat Flying Squirrels
Pocket Gophers Red Squirrel
Red Tree Vole
American Pika


Gnawing mammals with two pairs of incisors

American Pika Snowshoe Hare
Swamp Rabbit
Nine Banded Armadillo

Moles and Armadillos

Burrowing mammals

Moles Nine-Banded Armadillo
Subcribe to National Wildlife Magazine
Subcribe to National Wildlife Magazine

Get Involved

Where We Work

More than one-third of U.S. fish and wildlife species are at risk of extinction in the coming decades. We're on the ground in seven regions across the country, collaborating with 52 state and territory affiliates to reverse the crisis and ensure wildlife thrive.

Learn More
Regional Centers and Affiliates