Geese flying east into cover (5)
I believe the answer is:
skein
'geese flying' is the definition.
'east into cover' is the wordplay.
'east' becomes 'e' ('E' can be a synonym of 'east').
'into' is an insertion indicator.
'cover' becomes 'skin' (skin is a kind of cover**).
'e' inserted within 'skin' is 'SKEIN'.
(Other definitions for skein that I've seen before include "Coil of wool - flock of geese" , "Ball of yarn" , "Coiled length of yarn" , "Piece of loose-coiled yarn" , "A number of birds" .)