Traveller taking responsibility for vanished bird
I believe the answer is:
passenger pigeon
'vanished bird' is the definition.
'passenger pigeon' can be an answer for 'bird' (passenger pigeon is a kind of bird). I am unsure of the 'vanished' bit.
'traveller taking responsibility' is the wordplay.
'traveller' becomes 'passenger' (passenger is a kind of traveller).
'taking responsibility' becomes 'pigeon' (I can't explain this - if you can you should give a lot more credence to this answer).
'passenger'+'pigeon'='PASSENGER-PIGEON'
'for' is the link.
Can you help me to learn more?
(Other definitions for passenger pigeon that I've seen before include "long-distance flyer" , "Extinct migratory bird" .)