Water birds (5)
I believe the answer is:
geese
'water birds' is the definition.
(goose is a kind of water bird)
This is all the clue.
(Other definitions for geese that I've seen before include "They're seen in a gaggle" , "Birds that fly in a skein" , "Ganders" , "Domesticated birds" , "Large birds of the duck family" .)