River and loch bird (5)
I believe the answer is:
ousel
'bird' is the definition.
(ousel is a kind of bird)
'river and loch' is the wordplay.
'river' becomes 'ouse' (Yorkshire river).
'and' says to put letters next to each other.
'loch' becomes 'l'.
'ouse'+'l'='OUSEL'
(Other definitions for ousel that I've seen before include "Archaic name for blackbird" , "Strange louse for a blackbird" , "Thrush from Seoul, strangely" , "Louse turned out to be a thrush (5)." , "Ring bird" .)