Common songbird (5)
(Other definitions for robin that I've seen before include "good fellow in the D [DREAM]" , "Famous outlaw" , "Bird; Batman's aide" , "Day was one" , "Bird; man's name" .)
'common songbird' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for wren that I've seen before include "Very small brown songbird with erect tail" , "Member of the former Women's Royal Naval Service" , "Tiny brown songbird with a short upright tail" , "Small bird - great architect" , "Farthing's emblem" .)