Noisy bird with crest finally replaced by quiet dog (8)
I believe the answer is:
cockapoo
'dog' is the definition.
(I've seen this before)
'noisy bird with crest finally replaced by quiet' is the wordplay.
I cannot quite see how this works, but
'bird' could be 'cock' (cock is a kind of bird) and 'cock' is found in the answer.
'quiet' could be 'p' (music symbol for 'piano', ie soft or quiet) and 'p' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for cockapoo that I've seen is " dog".)