Feel remorse for beheading bird (5)
I believe the answer is:
egret
'bird' is the definition.
(egret is a kind of bird)
'feel remorse for beheading' is the wordplay.
'feel remorse for' becomes 'regret' (I've seen this before).
'beheading' means to remove the first letter.
'regret' with its initial letter taken off is 'EGRET'.
(Other definitions for egret that I've seen before include "Type of heron" , "White wading-bird" , "Water-bird, has plume" , "Kind of white heron - greet it" , "flier" .)