Crossword Genius

A songbird, or a couple of bovines, do we hear? (6)

Ross

I believe the answer is:

bulbul

'a songbird' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

(Other definitions for bulbul that I've seen before include "sweet singer" , "Tropical singer" .)

I've seen this clue in The Times.
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