Feel sorry for topless bird (5)
I believe the answer is:
egret
'bird' is the definition.
(egret is a kind of bird)
'feel sorry for topless' is the wordplay.
'feel sorry for' becomes 'regret' (I've seen this before).
'topless' means to remove the first letter.
'regret' with its initial letter taken away is 'EGRET'.
(Other definitions for egret that I've seen before include "Long-plumed heron" , "Kind of heron with long white feathers" , "Mainly white heron" , "Bird eating fish" , "Lesser white heron" .)