Lament of man about extinct bird (6)
I believe the answer is:
bemoan
'lament' is the definition.
('bemoan' can be a synonym of 'lament')
'man about extinct bird' is the wordplay.
'man' becomes 'ben' (**).
'about' means one lot of letters goes inside another.
'extinct bird' becomes 'moa' (extinct flightless bird of New Zealand).
'ben' placed around 'moa' is 'BEMOAN'.
'of' acts as a link.
(Other definitions for bemoan that I've seen before include "Complain about, lament" , "Lament, grieve" , "Deplore, lament" , "Regret, lament" .)