6. Swifts
Swifts are true aerial acrobats, spending up to ten months of the year in continuous flight. To rest during these marathon journeys, they rely on unihemispheric sleep, allowing one half of their brain to nap while the other stays alert for navigation.
Swifts alternate between brief naps and effortless gliding, making sleep mid-air a key survival skill. This incredible adaptation lets them remain airborne longer than any other bird. Reference