Person imitating bird like a thrush or robin initially (8)
I believe the answer is:
emulator
'person imitating' is the definition.
I can't judge whether this definition defines the answer.
'bird like a thrush or robin initially' is the wordplay.
'bird' becomes 'emu' (emu is a type of bird).
'like a' becomes 'la' (I can't justify this - if you can you should give a lot more credence to this answer).
'initially' says to take the initial letters.
The initial letters of 'thrush or robin' is 'tor'.
'emu'+'la'+'tor'='EMULATOR'
Can you help me to learn more?
(Other definitions for emulator that I've seen before include "rival" , "One copies the behaviour of another" , "Ape" , "Imitator" .)