Bird at two parties (4)
I believe the answer is:
dodo
'bird' is the definition.
(dodo is a kind of bird)
'at two parties' is the wordplay.
'two parties' means two substitutions for 'party'.
'at' says to put letters next to each other.
'party' becomes 'do' (do can informally mean a party).
'party' becomes 'do' (do can informally mean a party).
'do'+'do' is 'DODO'.
(Other definitions for dodo that I've seen before include "Square" , "silly person" , "Native of Mauritius" , "Old fogey" , "one very dead!" .)