The noisy fellow imitated birds! (4)
I believe the answer is:
flew
'imitated birds' is the definition.
Although both the answer and definition are past participle verbs, I can't understand how one could define the other.
'the noisy fellow' is the wordplay.
'the noisy' becomes 'f'.
'fellow' becomes 'lew' (I can't justify this - if you can you should give a lot more credence to this answer).
'f'+'lew'='FLEW'
Can you help me to learn more?
(Other definitions for flew that I've seen before include "Went quickly" , "bolted" , "Took off" , "Rushed (by air?)" , "Dashed" .)