Very cold poles for birds (8)
I believe the answer is:
bitterns
'birds' is the definition.
(bittern is a kind of bird)
'very cold poles' is the wordplay.
'very cold' becomes 'bitter' (bitter informally can mean very cold).
'poles' becomes 'NS' (north and south poles).
'bitter'+'ns'='BITTERNS'
'for' acts as a link.
(Other definitions for bitterns that I've seen before include "Marsh birds" , "Small herons with loud cries" , "Waders" , "Bert isn't involved with heron-like birds" .)