Animal and two ducks by river (3)
I believe the answer is:
roo
'animal' is the definition.
(I've seen this before)
'two ducks by river' is the wordplay.
'two ducks' becomes 'oo'.
'by' is a charade indicator (letters next to each other).
'river' becomes 'r' (abbreviation for river).
'oo' after 'r' is 'ROO'.
'and' is the link.
(Other definitions for roo that I've seen before include "large animal" , "Kanga's son (Pooh)" , "Aussie jumper!" , "Kanga's child (Pooh)" , "Kanga's baby (Pooh)" .)