Boast made by head of chorus line (4)
I believe the answer is:
Here is my best explanation:
'boast' is the definition.
(crow is a kind of boast)
'head of chorus line' is the subsidiary indication.
'head of' indicates taking the first letters.
'line' becomes 'row' (row is a kind of line).
The initial letter of 'chorus' is 'c'.
'made by' is the link.
(Other definitions for crow that I've seen before include "Black bird with raucous call", "Bird - birdcall", "'As the - - flies'", "Express gleeful triumph", "Make sound of cock - bird", "Boast, swagger, triumph", "Boast; bird", "Brag; carrion bird", "Native American -- bird" and "Make sounds of pleasure as a baby does - or a bird".)