Maternal bird? (4)

I believe the answer is:

tern

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'maternal bird?' is the definition.
'tern' can be an answer for 'bird?' (tern is a kind of bird). I'm unsure of the 'maternal' bit.

'maternal bird?' is the wordplay.
'maternal' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'bird?' becomes 'ern' (ern is a kind of bird).
't'+'ern'='TERN'

Can you help me to learn more?

(Other definitions for tern that I've seen before include "flier" , "Small gull with forked tail" , "Seagull" , "Rent out the bird" , "Gull-like sea bird" .)

I've seen this clue in the Evening Standard.

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