Hastened to protect extremely vulnerable bird (5)
I believe the answer is:
raven
'bird' is the definition.
(raven is a kind of bird)
'hastened to protect extremely vulnerable' is the wordplay.
'hastened' becomes 'ran' (I've seen this before).
'to protect' indicates putting letters inside (inserted letters are protected or taken in).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'vulnerable' with its centre removed is 've'.
'ran' placed around 've' is 'RAVEN'.
(Other definitions for raven that I've seen before include "Crow-like bird" , "Large blue-black bird" , "Bird with hoarse, croaking cry" , "Jet-black" , "Large black bird" .)