Island in France that's south of Bird Island (10)
I believe the answer is:
martinique
'island' is the definition.
(Martinique is a Caribbean island)
'island in france that's south of bird' is the wordplay.
'island' becomes 'i'.
'in france that' becomes 'que' ('that' in French).
'south of' is a charade indicator (letters next to each other).
'bird' becomes 'martin' (martin is a kind of bird).
'i'+'que'='ique'
'ique' put after 'martin' is 'MARTINIQUE'.
(Other definitions for martinique that I've seen before include "French Caribbean island" , "French island in the West?Indies" , "Caribbean spot" .)