Flightless birds share a dog's dinner (5)

I believe the answer is:

rheas

I'm a little stuck... Click here to teach me more about this clue!

'flightless birds' is the definition.
(rhea is a kind of flightless bird)

'share a dog's dinner' is the wordplay.
'share' anagrams to 'RHEAS'.
But, I am unsure how this is indicated.

Can you help me to learn more?

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

I've seen this clue in The Times.

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