Perch in river and ducks on street (5)
I believe the answer is:
roost
'perch' is the definition.
(roost is a kind of perch)
'river and ducks on street' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'and' means one lot of letters go next to another.
'ducks' becomes 'oo' (duck means zero in cricket).
'on' means one lot of letters go next to another.
'street' becomes 'st' (abbreviation).
'r'+'oo'+'st'='ROOST'
'in' is the link.
(Other definitions for roost that I've seen before include "where fliers land" , "Glowing with joy" , "Bats' settling place" , "Bat's resting place" , "Bird's settling place" .)