Bird edges round cake crumb (5)
I believe the answer is:
piece
'crumb' is the definition.
(thesaurus)
'bird edges round cake' is the wordplay.
'bird' becomes 'pie' (sort of bird**).
'edges round' means to remove the middle letters (only the edge letters remain).
'cake' with its middle taken out is 'ce'.
'pie'+'ce'='PIECE'
(Other definitions for piece that I've seen before include "Portion, bit" , "bishop on board, say" , "Section; firearm" , "Bit; item" , "constituent" .)