Bird has single cocktail (7)
I believe the answer is:
martini
'cocktail' is the definition.
(martini is a kind of cocktail)
'bird has single' is the wordplay.
'bird' becomes 'martin' (martin is a kind of bird**).
'has' means one lot of letters go next to another.
'single' becomes 'i' (one).
'martin'+'i'='MARTINI'
(Other definitions for martini that I've seen before include "In glass, one's dry" , "Cocktail of gin and dry vermouth" , "Italian drink" , "Type of Italian vermouth" , "James Bond's drink of choice" .)