Dismal criminal getting bird (7)

I believe the answer is:

greylag

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

'dismal criminal' is the wordplay.
'dismal' becomes 'grey' (I can't explain this - if you can you should give a lot more credence to this answer).
'criminal' becomes 'lag' (slang term for a prisoner).
'grey'+'lag'='GREYLAG'

'getting' is the link.

Can you help me to learn more?

(Other definitions for greylag that I've seen before include "bird?" , "Breed of goose - Lyra egg (anag)" , "Large goose" , "Eurasian goose" , "Wild goose -- eg gyral (anag)" .)

I've seen this clue in The Sunday Times.

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