Duck occupying river delta perch (3)
I believe the answer is:
rod
'perch' is the definition.
('rod' can be a synonym of 'perch')
'duck occupying river delta' is the wordplay.
'duck' becomes 'o'.
'occupying' indicates putting letters inside.
'river' becomes 'r'.
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'r'+'d'='rd'
'o' inserted inside 'rd' is 'ROD'.
(Other definitions for rod that I've seen before include "Angler's cane" , "that most anglers use" , "Wand - fishing stick" , "Straight, slender stick" , "Angler's equipment" .)