Small birds get cold feet (5)
I believe the answer is:
quail
'small' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for quail that I've seen before include "Small bird of the partridge family" , "Game bird - cower" , "Cower before the game-bird?" , "Game bird; flinch" , "See little bird" .)