Skein fliers (5)
I believe the answer is:
geese
'skein fliers' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for geese that I've seen before include "Stupid people" , "Protectors of city" , "0 Water birds" , "Water birds related to ducks and swans" , "They come in gaggles and skeins" .)