Laura Erickson's For the Birds

I’ve seen Common Swifts in Austria during nesting season and in Uganda in winter but have no photos of them. They hold an entry in the Guinness Book of World Records:

Common Swift: Most airborne land bird. The most aerial bird is the common swift (Apus apus), which remains airborne for two to four years, during which time it sleeps, drinks, eats and even mates on the wing. It has been calculated that a young swift completes a non-stop flight of 500,000 km 310,000 miles between fledging and its first landing at a potential nesting site two years later.

Other swifts may also accomplish this exact same feat.