Pelican that’s no more, unfortunately right after feline enters (8)

'pelican that's no more' is the definition.
(historical term for a pelican)

'unfortunately right after feline enters' is the wordplay.
'unfortunately' becomes 'alas' ('alas' is used to express regret).
'right' becomes 'r' (common abbreviation).
'after' says to put letters next to each other.
'feline' becomes 'cat' (cat is a kind of feline).
'enters' means one lot of letters goes inside another.
'r' after 'cat' is 'catr'.
'alas' enclosing 'catr' is 'ALCATRAS'.