Humming birds long ago heading off across border into Peru, finally (7)
I believe the answer is:
odorous
'humming birds long ago heading' is the definition.
I can't tell whether this defines the answer.
'off across border into peru finally' is the wordplay.
'off' becomes 'odos' (I can't justify this - if you can you should believe this answer much more).
'across' indicates putting letters inside.
'finally' indicates one should take the final letters.
The final letters of 'border into peru' are 'rou'.
'odos' enclosing 'rou' is 'ODOROUS'.
Can you help me to learn more?
(Other definitions for odorous that I've seen before include "Scented" , "having a distinct aroma" , "Fragrant" , "Sweet-smelling" , "Smelly" .)