Mother protecting egg? This bird has gone! (3)
I believe the answer is:
moa
'this bird has gone' is the definition.
'moa' can be an answer for 'bird' (extinct flightless bird of New Zealand). I am unsure of the remainder of the definition.
'mother protecting egg?' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'protecting' is an insertion indicator (inserted letters are held or protected).
'egg?' becomes 'o' (an 'o' resembles an egg).
'ma' enclosing 'o' is 'MOA'.
Can you help me to learn more?
(Other definitions for moa that I've seen before include "Early bird" , "Bird that died out" , "Extinct large flightless NZ bird" , "Bird no longer" , "Bird lost" .)