Watcher of The Birds, one showing nervousness (8)

I believe the answer is:

twitcher

I believe this is a double definition.

'watcher of the birds' is the first definition.
(birdwatchers are called twitchers)

'one showing nervousness' is the second definition.
(someone who twitches)

(Other definitions for twitcher that I've seen before include "One not still" , "Bird watcher" , "Rare bird spotter" , "Measure; creep" , "Bird-watcher (colloq)" .)

I've seen this clue in The Times.

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