Roosted (7)
'roosted' is the definition.
('perch' can be a synonym of 'roost')
This is the entire clue.
(Another definition for perched that I've seen is " Sat on a branch".)
(Other definitions for nested that I've seen before include "Inhabited an egg-laying place" , "Of bird, settled in to home" , "Fitted inside one another, say set of tables" , "intricate arrangement" , "Settle in comfortably like a bird" .)