Bird identified by crows? (7)

I believe the answer is:

rooster

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'bird' is the definition.
(I know that rooster is a type of Gallus gallus)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for rooster that I've seen before include "Crowing bird" , "Adult male chicken" , "Cockerel (mainly US)" , "Farmyard cock" , "Toreros (anag.)" .)

I've seen this clue in The Telegraph.

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