Bird beginning to sing along with a musician (9)
I believe the answer is:
sandpiper
'bird' is the definition.
(sandpiper is a kind of bird)
'beginning to sing along with a musician' is the wordplay.
'beginning to' indicates taking the first letters.
'along with' becomes 'and' (I've seen this in another clue).
'a musician' becomes 'piper' (someone playing the bagpipes).
The first letter of 'sing' is 's'.
's'+'and'+'piper'='SANDPIPER'
(Other definitions for sandpiper that I've seen before include "Small wading bird with a slender bill" , "Ground-dwelling wading bird" , "Coastal wading bird" , "Stint" , "winger" .)