Scotsman goes after a number of birds (5)
I believe the answer is:
avian
'of birds' is the definition.
(I've seen this before)
'scotsman goes after a number' is the wordplay.
'scotsman' becomes 'ian'.
'goes after' is a charade indicator (letters next to each other).
'a number' becomes 'av' (I've seen this in other clues).
'ian' after 'av' is 'AVIAN'.
(Other definitions for avian that I've seen before include "To do with birds - like a dangerous flu" , "Lizard with adhesive foot-pads" , "Like a booby" , "Pertaining to or characteristic of birds" , "Like rails, for example" .)