It doesn't have to be smart to fool the birds (9)
I believe the answer is:
scarecrow
'it doesn't have' is the definition.
The definition suggests a singular noun which matches the answer.
'be smart to fool the birds' is the wordplay.
I cannot quite understand how this works, but
'be' could be 'are' (I've seen this in another clue) and 'are' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?
(Other definitions for scarecrow that I've seen before include "Ragged figure in field" , "Man of straw" , "One in 5d's party" , "crude figure" , "6 [FRIEND OF DOROTHY]" .)