Mad about a bird (5)
I believe the answer is:
rabid
'mad' is the definition.
(I've seen this in another clue)
'about a bird' is the wordplay.
'about' indicates an anagram.
'a'+'bird'='abird'
'abird' with letters rearranged gives 'RABID'.
(Other definitions for rabid that I've seen before include "Mad; raging" , "Violent; hydrophobic" , "Ill from a mad dog bite?" , "Raging (having been bitten by a dog?)" , "Extreme, fanatical" .)