Couple under par get the bird! (5)

I believe the answer is:

eagle

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

I can't explain the rest of the clue.

(Other definitions for eagle that I've seen before include "Aglee (anag.)" , "good score" , "A glee-ful bird?" , "Flyer" , "The emblem of the US is bald" .)

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

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