Bird left in mesh (6)
I believe the answer is:
linnet
'bird' is the definition.
(linnet is a kind of bird)
'left in mesh' is the wordplay.
'left' becomes 'l' (common abbreviation).
'mesh' becomes 'net' ('net' can be a synonym of 'mesh').
'l'+'in'+'net'='LINNET'
(Other definitions for linnet that I've seen before include "House finch" , "Songster" , "Singer" , "Passerine bird" , "Bird in the finch family" .)