Birds of prey often highly strung (5)

I believe the answer is:

kites

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

I don't understand how the rest of the clue works.

(Other definitions for kites that I've seen before include "aircraft" , "They're flown in the wind at the end of a string" , "Aerial toys; birds" , "Large hawks or flying toys" , "More than one toy" .)

I've seen this clue in The Globe and Mail.

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