Bird in Sun a lot, rolling over (7)
I believe the answer is:
ortolan
'bird' is the definition.
(ortolan is a kind of bird)
'in sun a lot rolling over' is the wordplay.
'in' indicates a hidden word.
'over' says the letters should be written in reverse.
'nalotro' is hidden in the letters of 'sun a lot rolling'.
'nalotro' written backwards gives 'ORTOLAN'.
(Other definitions for ortolan that I've seen before include "Bird" , "Type of bunting eaten as a delicacy" , "Bobolink" , "One flying" , "European bunting" .)