Highly important songbird (8)
I believe the answer is:
cardinal
This could be a double definition.
'highly important' is the first definition.
'cardinal' can be an answer for 'important' (similar in meaning). I'm not sure about the 'highly' bit.
'songbird' is the second definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for cardinal that I've seen before include "Senior Roman Catholic" , "fundamental importance" , "Principal - churchman" , "Prince of the Roman Catholic Church" , "Scarlet; fundamental" .)