Bird flavour? Without a hesitation! (7)
I believe the answer is:
tanager
'bird' is the definition.
(I know that tanager is a type of oscine)
'flavour? without a hesitation' is the wordplay.
'flavour?' becomes 'tang' ('tang' can be a synonym of 'flavour').
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'tang' placed around 'a' is 'tanag'.
'tanag'+'er'='TANAGER'
(Other definitions for tanager that I've seen before include "A bird" , "American songbird" , "Songbird of the bunting family" , "South American singer" .)