Caspian Tern

The Caspian tern is named after the Caspian Sea and is the world's largest tern. It has a white head, neck, belly and tail and black cap, legs, and wing tips on the underside. In winter the cap gets streaks of white, which is how the terns I saw looked. The upper wings and back are pale gray and the distinctive bill is long, thick and a loud red/orange with a small black tip. 

The black cap is heavily inundated with white. The black near the end of the bill is very light. 

The cap on the other bird is darker, as is the black near the end of the bill. 

In the U.S., they winter in Florida, along the Gulf Coast of Texas and Louisiana and the Atlantic Coast of Georgia and the Carolinas. They breed in the summer in areas around the Great Lakes and small portions of California, Utah, Idaho, Oregon and Washington. The world's largest breeding colony is 6,000 pairs on an artificial island in the Columbia River between Oregon and Washington. 

I saw these two Caspian terns in Orlando Wetlands Park near Christmas, Florida. They are strikingly beautiful.