Bird, or a form of louse (5)
I believe the answer is:
ousel
'bird' is the definition.
(ousel is a kind of bird)
'a form of louse' is the wordplay.
'a form of' indicates anagramming the letters (another form of the same letters).
'louse' with letters rearranged gives 'OUSEL'.
'or' is the link.
(Other definitions for ousel that I've seen before include "dipper" , "Flyer" , "Bird similar to blackbird" , "it goes flying" , "Louse turned out to be a thrush (5)." .)