Head of shockingly pale bird (4)
I believe the answer is:
swan
'bird' is the definition.
(swan is a kind of bird)
'head of shockingly pale' is the wordplay.
'head of' suggests taking the first letters.
'pale' becomes 'wan' ('wan' can be a synonym of 'pale').
The initial letter of 'shockingly' is 's'.
's'+'wan'='SWAN'
(Other definitions for swan that I've seen before include "Large, long-necked bird" , "possibly mute" , "Whooper or trumpeter?" , "black, in 7th" , "Graceful bird" .)