The male of this duck has a dark head with a white cheek patch (9)

I believe the answer is:

goldeneye

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'the male of this duck' is the definition.
'goldeneye' can be an answer for 'duck' (type of duck). I'm not certain of the remainder of the definition.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for goldeneye that I've seen before include "Northern diving duck - 1995 Bond film" , "spy film" .)

I've seen this clue in The Times.

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