Perch from river, and ducks, extremely succulent (5)
I believe the answer is:
roost
'perch' is the definition.
('roost' can be a synonym of 'perch')
'river and ducks extremely succulent' is the wordplay.
'river' becomes 'r'.
'and' means one lot of letters go next to another.
'ducks' becomes 'oo' (I've seen this in other clues).
'extremely' means to remove the middle letters.
'succulent' with its centre removed is 'st'.
'r'+'oo'+'st'='ROOST'
'from' acts as a link.
(Other definitions for roost that I've seen before include "Henhouse" , "It's sometimes ruled" , "Place where birds rest" , "Thin paper" , "Place for sleeping birds" .)