Sticky stuff used internally for bird (5)
I believe the answer is:
goose
'for bird' is the definition.
(goose is a kind of bird)
'sticky stuff used internally' is the wordplay.
'sticky stuff' becomes 'goo' (goo is a sticky substance).
'internally' indicates the central letters.
The centre of 'used' is 'se'.
'goo'+'se'='GOOSE'
(Other definitions for goose that I've seen before include "Bird; foolish person" , "Gander's mate" , "Supposedly foolish bird" , "Bird - tailor's iron" , "Web-footed long-necked bird" .)