Birds protecting a corner make a defiant gesture (4,1,5)
I believe the answer is:
cock a snook
'a defiant gesture' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'birds protecting a corner' is the wordplay.
'birds' becomes 'cocks' (cock is a kind of bird).
'protecting' means one lot of letters goes inside another.
'corner' becomes 'nook' (synonyms).
'cocks' going around 'a' is 'cockas'.
'cockas'+'nook'='COCK A SNOOK'
'make' acts as a link.
Can you help me to learn more?
(Other definitions for cock a snook that I've seen before include "Show contempt (with thumb touching nose and fingers spread)" , "Gesture contemptuously" .)