Birds, in spirit, rejected their food (10)

I believe the answer is:

chickadees

I'm a little stuck... Click here to teach me more about this clue!

'birds' is the definition.
(chickadee is a kind of bird)

'spirit rejected their food' is the wordplay.
I cannot really understand how this works, but
'spirit' could be 'ka' (I've seen this in other clues) and 'ka' is found in the answer.
'food' could be 'e' (E is an example) and 'e' is present in the answer.
This explanation may well be incorrect...

'in' acts as a link.

Can you help me to learn more?

I've seen this clue in The Times and The Sunday Times.

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