Bird going underneath black dog (6)
I believe the answer is:
beagle
'dog' is the definition.
(beagle is a kind of dog)
'bird going underneath black' is the wordplay.
I cannot really understand how this works, but
'bird' could be 'eagle' (eagle is a type of bird) and 'eagle' is present in the answer.
'black' could be 'b' (as in pencil classifications) and 'b' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for beagle that I've seen before include "Darwin voyaged in this ship" , "Small short-legged hound" , "Short-haired dog" , "Small, sturdy breed of hound" , "hunting animal with smooth coat" .)