Four of the upsetting possibilities for wading bird (4)

I believe the answer is:

ibis

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'wading bird' is the definition.
(ibis is a kind of wading bird)

I don't understand the rest of the clue.

(Other definitions for ibis that I've seen before include "Wading bird with a down-curved bill" , "Wading bird of tropical waters" , "Wading bird sacred to the Egyptians" , "Retreat" , "Wader with a long down-curved bill" .)

I've seen this clue in The Irish Times.

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