A bird dog by name (6)
I believe the answer is:
curlew
'a bird' is the definition.
(curlew is a kind of bird)
'dog by name' is the wordplay.
'dog' becomes 'cur' (cur is a kind of dog).
'by' means one lot of letters go next to another.
'name' becomes 'lew' (**).
'cur'+'lew'='CURLEW'
(Other definitions for curlew that I've seen before include "Wading bird with long down-curved beak" , "Flyer" , "Curve-beaked bird" , "Shorebird of the sandpiper family" , "Large wader of the sandpiper family" .)