Supremo, preening, swimming birds (7,8)

I believe the answer is:

emperor penguins

'birds' is the definition.
(emperor penguin is a kind of bird)

'supremo preening swimming' is the wordplay.
'swimming' indicates anagramming the letters.
'supremo'+'preening'='supremopreening'
'supremopreening' is an anagram of 'EMPEROR PENGUINS'.

I've seen this clue in the Sydney Morning Herald.

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