The area now housing Yellowstone National Park is the only place in the continental United States where American bison have continually lived since prehistoric times.
Female bison give birth to one calf every year, usually in April or May, so visit Yellowstone in the spring if you want baby photos.
(Courtesy Ed Thomes Photography/Flickr)
In Denali National Park, golden eagles outnumber bald eagles by 70 percent.
Golden eagles, which are migratory, can best be seen in Denali National Park mid-March through September, before they head south for the winter.
The northern elephant seal is one of four types of pinnipeds (or "fin-footed" mammals) commonly found in Southern California's Channel Islands National Park.
The five isolated islands that make up the Channel Islands National Park are home to one of the largest gatherings of marine mammals on the planet, with over 50,000 northern elephant seals alone breeding here each year.
Named for Theodore Roosevelt, father of the American national parks system, the Roosevelt elk is the largest of the North American elk subspecies.
President Theodore Roosevelt had a direct hand in creating the Mt. Olympus National Monument in 1909 to protect the elk living on Washington's Olympic Peninsula.
The coyote thrives in both urban and wilderness areas, especially the peak-filled Rocky Mountain National Park, an hour north of Boulder, Colorado.
Smart, resourceful, and adaptable, the coyote has historically been the target of farmers and ranchers who view them as a threat to livestock.
Weighing in at up to 300 pounds, the mountain goat navigates the rocky terrain of Glacier National Park thanks to hooves that are embedded with excellent traction pads and sharp, slip-preventing dewclaws.
With six mountains over 10,000 feet high, Glacier National Park is a perfect habitat for the shaggy, white mountain goat.
The subtropical wetlands that make up Florida's Everglades National Park are the only environment in the world where alligators (above) and crocodiles live together in harmony.
The alligator (above) has a broader snout than the crocodile.
The rare pronghorn is commonly known as the "pronghorn antelope," although it doesn't technically qualify as one.
Labeled endangered in the 1920s, the pronghorn can reach speeds of up to 60 mph, making it the fastest land mammal in North America.
The highly social prairie dog lives in underground colonies, or "towns," that can include as many as 26 family members.
In Texas's Big Bend National Park, the mountain lion is the lord of the manor, a top predator that feasts on deer, javelinas, and other herbivores.
With its striking gold-scale-flecked black body, white chin, bright yellow iris, and blue face, the French angelfish stands out in a crowd in Virgin Islands National Park.
Native to the western Atlantic, Gulf of Mexico, and Caribbean, the French angelfish usually hangs out around shallow reefs.
Smaller and more tolerant of humans than their grizzly cousins, black bears are the official symbol of Great Smoky Mountains National Park.
It's estimated that about 1,500 bears currently live in Great Smoky Mountains National Park; that comes out to about two bears per square mile.