Fliers
'fliers' is the definition.
(I know this)
This is all the clue.
(Other definitions for pilots that I've seen before include "They fly aircraft and guide ships into harbour" , "Flies" , "Shepherds" , "Airmen" , "They are licensed to fly aircraft" .)
(Other definitions for birds that I've seen before include "Gulls" , "Egg-laying vertebrates" , "Terns and tits, say" , "Feathered fliers" , "4th" .)