Birds of prey decapitated chickens (4)

I believe the answer is:

owls

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'birds of prey' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for owls that I've seen before include "Wise old birds - quite slow" , "Slow sort of birds" , "Members of Parliament" , "Nocturnal hooters?" , "Nocturnal bird" .)

I've seen this clue in The Guardian.

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