The
extensive white on the underwing and the delicate beak confirm that
this is a Zino's - compare the bill with a Fea's Petrel here
To see this species in daylight one really needs to take a pelagic
trip. The alternative is to visit the breeding colonies at night -
something I did not find time to do myself during my visit to Madeira.
This night time visit is an unforgetable experience according to those
I have spoken to about it.