Bird’s repeated note (4)
I believe the answer is:
dodo
'bird's' is the definition.
(dodo is a kind of bird)
'repeated note' is the wordplay.
'repeated' says to double the letters.
'note' becomes 'do' (musical note, as in do-re-mi).
'do' doubled is 'DODO'.
(Other definitions for dodo that I've seen before include "Old bird" , "Old fogey" , "Repetitive extinct animal" , "Old-fashioned person" , "Proverbially dead bird" .)