A former soldier collars military leader, giving the bird (6)
I believe the answer is:
avocet
'the bird' is the definition.
(avocet is a kind of bird)
'a former soldier collars military leader' is the wordplay.
'former soldier' becomes 'vet' (short for veteran).
'collars' means one lot of letters goes inside another (to collar can mean to apprehend or capture).
'military leader' becomes 'OC' (abbreviation for Officer Commanding).
'vet' placed around 'oc' is 'vocet'.
'a'+'vocet'='AVOCET'
'giving' acts as a link.
(Other definitions for avocet that I've seen before include "Shorebird - octave (anag)" , "Wading bird with long bill" , "RSPB emblem" , "Flier" , "Long-legged wading bird with upward-curving bill" .)