Bird in sorrow first to be dumped (5)
I believe the answer is:
egret
'bird' is the definition.
(egret is a kind of bird)
'sorrow first to be dumped' is the wordplay.
'sorrow' becomes 'regret' (regret is a kind of sorrow).
'first to be dumped' means to remove the first letter.
'regret' with its initial letter taken away is 'EGRET'.
'in' acts as a link.
(Other definitions for egret that I've seen before include "Type of forty eight Ac" , "White-feathered wading bird" , "Lesser white heron" , "Long-plumed heron" , "Seabird" .)