The bird flew out one day (5)
I believe the answer is:
raven
'the bird' is the definition.
(raven is a kind of bird)
'flew out one day' is the wordplay.
'flew' becomes 'ran' (I've seen this in another clue).
'out' means to remove the last letter.
'one day' becomes 'ven' (I can't justify this - if you can you should give a lot more credence to this answer).
'ran' with its last letter taken away is 'ra'.
'ra'+'ven'='RAVEN'
Can you help me to learn more?
(Other definitions for raven that I've seen before include "Large black bird" , "Flyer" , "Flier" , "Flighty type" , "Large bird of the crow family" .)