Bird to get down suddenly (4)

I believe the answer is:

duck

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'bird' is the definition.
(duck is a kind of bird)

I cannot understand how the rest of the clue works.

(Other definitions for duck that I've seen before include "Quacker?" , "Dear; bird; fabric" , "Bob" , "eg Jemima, Donald" , "Shoveler, for example" .)

I've seen this clue in The Times.

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