Continue to protect a bird (4,2,2)
I believe the answer is:
keep at it
'continue' is the definition.
(thesaurus)
'protect a bird' is the wordplay.
'protect' becomes 'keep' (keeping is a kind of protecting).
'bird' becomes 'tit' (tit is a kind of bird).
'keep'+'a'+'tit'='KEEP AT IT'
'to' is the link.
(Other definitions for keep at it that I've seen before include "Persevere" , "Continue" , "carry on" .)