The Don Edwards San Francisco Bay National Wildlife Refuge in California is one of 555 refuges in the country. The salt marshes at the refuge were put to use following the California 1849 gold rush when tens of thousands of acres were turned into commercial salt ponds, but now they provide critical habitat for migratory birds.
Pelicans fly during sunset at the Sonny Bono Salton Sea National Wildlife Refuge near Calipatria, Calif. The site is a major stop on the Pacific Flyway, a north-south route for migratory birds that runs between Alaska and Patagonia.
A mountain goat and kid stand above the tree line in Kodiak National Wildlife Refuge in Kodiak, Alaska. Summer in Kodiak is prime time for researchers, who otherwise cannot access much of the refuge because of ice, snow and rough weather.
A herd of ponies makes its way toward shore during the Chincoteague Wild Pony Swim. The ponies swim from Chincoteague National Wildlife Refuge to Chincoteague Island, Va., to be sold at auction to benefit the Chincoteague Volunteer Fire Company.
Carbon dioxide from deep underground fissures bubbles up through geothermal mudpots, or mud volcanoes, over the southern San Andreas earthquake fault near the Sonny Bono Salton Sea National Wildlife Refuge.
A butterfly shares a blossom with bees at Merritt Island National Wildlife Refuge near Titusville, Fla. The refuge shares a boundary with the John F. Kennedy Space Center.
The Haklau Forest National Wildlife Refuge koa reforestation project on the flank of the Mauna Kea volcano on the Big Island of Hawaii is seen Sept. 23 from above.
A Laysan albatross, also called a gooney bird, incubates its eggs on Midway Island in the Midway Atoll National Wildlife Refuge. Nearly 3 million birds reside here for much of each year.
A young buffalo's breath swirls around it at Sullys Hill National Game Preserve, N.D., as the herd of 38 animals waits to be transported to its new home at Fort Niobrara National Wildlife Refuge in Nebraska.
A federal bird biologist conducts shore bird research inside the Yukon Delta National Wildlife Refuge in southwest Alaska.
An egret flies over the waters of Flint Creek in the Wheeler National Wildlife Refuge in Decatur, Ala. The water reflects the red leaves on trees lining the creek bank.
A herd of musk ox graze in an area of the Arctic National Wildlife Refuge in Alaska. The average height of these hardy animals is about 4 feet at the shoulder.