Scared small birds (8)
I believe the answer is:
chickens
'birds' is the definition.
(chicken is a kind of bird)
'scared small' is the wordplay.
'scared' becomes 'chicken'.
'small' becomes 's' (abbreviation - e.g. clothes size).
'chicken'+'s'='CHICKENS'
(Other definitions for chickens that I've seen before include "Domestic fowl" , "farmyard animals?" , "Yellow" , "Young fowl" , "Don't count these before they're hatched" .)