Bird, dog, donkey and polled Hereford? (8)

I believe the answer is:

curassow

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'bird' is the definition.
(I know that curassow is a type of gallinacean)

'dog donkey and polled hereford?' is the wordplay.
'dog' becomes 'cur' (both can mean a despicable person).
'donkey' becomes 'ass' (ass is a term for a donkey).
'and' means one lot of letters go next to another.
'polled hereford?' becomes 'ow' (I can't explain this - if you can you should give a lot more credence to this answer).
'cur'+'ass'+'ow'='CURASSOW'

Can you help me to learn more?

(Another definition for curassow that I've seen is " Game bird".)

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

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