Popular seabird put in cage? (6)

I believe the answer is:

intern

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'in cage?' is the definition.
'intern' can be an answer for 'cage?' (I've seen this before). I am not sure about the 'in' bit.

'popular seabird' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'seabird' becomes 'tern' (tern is a kind of seabird).
'in'+'tern'='INTERN'

'put' acts as a link.

Can you help me to learn more?

(Other definitions for intern that I've seen before include "(American) hospital doctor" , "Imprison (enemy aliens)" , "Detain in custody" , "Hold in custody" , "Lock up the hospital doctor" .)

I've seen this clue in The Daily Mail.

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