perching (8)
I believe the answer is:
roosting
'perching' is the definition.
('roost' can be a synonym of 'perch')
This is the entire clue.
(Other definitions for roosting that I've seen before include "Trying to sleep" , "Perching, as fowl do" , "Sitting like a bird" , "Of birds, settling for sleep" , "in place of sleep?" .)