Hears about birds unable to fly (5)

I believe the answer is:

rheas

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'birds unable to fly' is the definition.
I can't judge whether this definition defines the answer.

'hears about' is the wordplay.
'about' indicates anagramming the letters.
'hears' anagrammed gives 'RHEAS'.

Can you help me to learn more?

(Other definitions for rheas that I've seen before include "these birds won't fly" , "Flightless birds" , "Ostrich-like birds" .)

I've seen this clue in The Telegraph.

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