Object when bird is taken in by doctor (5)
I believe the answer is:
demur
'object' is the definition.
(to demur is to object to something)
'bird is taken in by doctor' is the wordplay.
'bird' becomes 'emu' (emu is a type of bird).
'is taken in by' is an insertion indicator (back).
'doctor' becomes 'dr' (abbreviation).
'emu' put inside 'dr' is 'DEMUR'.
'when' is the link.
(Other definitions for demur that I've seen before include "Object gently" , "Hesitate from uncertainty or object" , "Politely disagree" , "Protest mildly, show reluctance" , "Raise objections" .)