Bird dog slipping lead (5)
I believe the answer is:
eagle
'bird' is the definition.
(eagle is a type of bird)
'dog slipping lead' is the wordplay.
'dog' becomes 'beagle' (beagle is a kind of dog).
'slipping lead' means to remove the first letter (I've seen 'slips lead' mean this).
'beagle' with its initial letter removed is 'EAGLE'.
(Other definitions for eagle that I've seen before include "Symbolic American bird" , "Bird of prey, may be golden" , "ten-dollar coin" , "good score" , "five buck bit, or more" .)