Small, pale flyer (4)
I believe the answer is:
swan
'flyer' is the definition.
(I know that Swan is a type of flyer)
'small pale' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'pale' becomes 'wan' (wan can mean pale or grey).
's'+'wan'='SWAN'
(Other definitions for swan that I've seen before include "Bird of Cygnus genus" , "Royal bird" , "Large, long-necked bird" , "Mute, whooper or Bewick's bird" , "Graceful bird" .)