The entire East Coast is on the Atlantic Flyway for migrating water birds and waterfowl. You can see them all the way from the Maine coast, particularly Monhegan and Machias islands, to the Wellfleet Wildlife Sanctuary on Cape Cod, and on south to Maryland's eastern shore, where Chincoteague National Wildlife Refuge (tel. 757/336-6122; www.fws.gov/northeast/chinco), on the Maryland-Virginia line, is the best bet.
Shorebirds also migrate along the Pacific side of the country, with good viewing anywhere along the Washington and Oregon coasts, but especially in Malheur National Wildlife Refuge in southeastern Oregon.
Once endangered, the bald eagle is now widespread across the country. Dozens make their winter home at Lake Cachuma near Santa Barbara in California. In January they flock to the Skagit River north of Seattle to feast on salmon, and you can even spot them while riding a Washington State ferry through the San Juan Islands. In September, look for them along Alaska's southeastern coast. Alaska also has many other birds not found in the lower 48 states.
In the Arizona desert, Ramsey Canyon Preserve is internationally known as home to 14 species of hummingbird, more than anywhere else in the United States. San Pedro Riparian National Conservation Area is another good spot in Arizona, with more than 300 species.
For tropical species, head to Florida, especially to Everglades National Park.
Hawaii's tropical birds are found nowhere else on earth, including the rare o'o, whose yellow feathers Hawaiians once plucked to make royal capes. Large colonies of seabirds nest at Kilauea National Wildlife Preserve and along the Na Pali Coast on Kauai, and Molokai's Kamakou Preserve is home to the Molokai thrust and Molokai creeper, found nowhere else.
For information about escorted bird-watching trips, contact Field Guides (tel. 800/728-4953 or 512/263-4795; www.fieldguides.com) or Victor Emanual Nature Tours (tel. 800/328-8368 or 512/328-5221; www.ventbird.com). The National Audubon Society (tel. 212/979-3000; www.audubon.org) runs superb bird-watching programs for both aspiring and experienced naturalists.