Stratagem used to catch a bird (3)
I believe the answer is:
emu
'a bird' is the definition.
(emu is a type of bird)
'stratagem used to catch' is the wordplay.
'to catch' indicates a hidden word (I've seen 'catches' mean this (the answer is caught in the clue)).
'EMU' is hidden within 'stratagem used'.
(Other definitions for emu that I've seen before include "Aussie runner" , "European project" , "Flightless bird of Australia, like ostrich" , "Ostrich-like bird" , "Large Australian flightless bird" .)