Small bird is to leave pronto (5)
I believe the answer is:
scoot
'to leave pronto' is the definition.
I can't judge whether this definition defines the answer.
'small bird' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'bird' becomes 'coot' (coot is a kind of bird).
's'+'coot'='SCOOT'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for scoot that I've seen before include "Move rapidly" , "Dart off" , "hightail it" , "hurry" , "Leave quickly" .)