Singer's large chest (4)
I believe the answer is:
lark
'singer's' is the definition.
(lark is a kind of birdanimal)
'large chest' is the wordplay.
'large' becomes 'l'.
'chest' becomes 'ark' (historical term for a chest).
'l'+'ark'='LARK'
(Other definitions for lark that I've seen before include "carefree adventure" , "Bird that sings on the wing" , "what one may get up to?" , "High-flying singer - frolic" , "Game - bird" .)