Bird of prey's new cry of distress south of Devon river (5,3)
I believe the answer is:
tawny owl
'bird of prey's' is the definition.
(tawny owl is a kind of bird of prey)
'new cry of distress south of devon river' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'cry of distress' becomes 'yowl' (I've seen this in another clue).
'south of' means one lot of letters go next to another (in a down clue, some letters go under others).
'devon river' becomes 'taw' (River Taw in Devon).
'n'+'yowl'='nyowl'
'nyowl' after 'taw' is 'TAWNY OWL'.
(Other definitions for tawny owl that I've seen before include "Common hooting bird" , "Bird of prey, Strix aluco" , "Deputy Brownie guider" , "hooter" .)