Rustic one bird devours (5)
I believe the answer is:
swain
'rustic' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'one bird devours' is the wordplay.
'one' becomes 'i' (Roman numeral).
'bird' becomes 'swan' (swan is a kind of bird).
'devours' is an insertion indicator (inserted letters are devoured).
'i' put within 'swan' is 'SWAIN'.
Can you help me to learn more?
(Other definitions for swain that I've seen before include "fancier" , "Boyfriend" , "Male admirer" , "Rustic suitor" , "Young man" .)