Bird hide is to be concealed (6)
I believe the answer is:
siskin
'bird' is the definition.
(siskin is a kind of bird)
'hide is to be concealed' is the wordplay.
'hide' becomes 'skin' ('skin' can be a synonym of 'hide').
'to be concealed' is an insertion indicator.
'skin' placed around 'is' is 'SISKIN'.
(Other definitions for siskin that I've seen before include "Type of bird" , "Yellow-and-black finch" , "Greenish songbird of finch family" , "Greenish songbird related to Goldfinch" , "Small songbird related to the goldfinch" .)