Pleased when bird joins a band (4,1,4)

I believe the answer is:

cock a hoop

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'pleased' is the definition.
(I've seen this before)

'bird joins a band' is the wordplay.
'bird joins' becomes 'cock' (I am not sure about this - if you are sure you should believe this answer much more).
'band' becomes 'hoop' (hoop is a kind of band).
'cock'+'a'+'hoop'='COCK-A-HOOP'

'when' acts as a link.

Can you help me to learn more?

(Other definitions for cock a hoop that I've seen before include "top of the world" , "in very high spirits" , "Excited" , "ecstatic" , "in raptures" .)

I've seen this clue in The Daily Express.

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