The bird outside, a nutcracker, is perky (6)

I believe the answer is:

jaunty

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'perky' is the definition.
('jaunty' can be a synonym of 'perky')

I cannot understand how the rest of the clue works.

(Other definitions for jaunty that I've seen before include "Cheerfully self-confident" , "Cheerful and self-confident, perhaps with a swagger" , "Sprightly and cheerful" , "Stylish" , "Happy" .)

I've seen this clue in the Evening Standard.

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