Shearwater Canary islands. (1 Viewer)

Hi, during my last trip to the canary islands i took a ferry from Gran Canaria to fuerteventura (22.04.15). I saw thousand of cory's shearwater, two gannet and a great skua.
Checking my photos i saw something that seems a different bird.
It don't seems brownish as the cory's but darker and slightly smaller.
It seems to have also a shoulder patch so me and some friend tought to great shearwater.
Unfortunely the head is not visible...
What do you think?

Thank you, bye
Marco Crivellari
Italy

Really tough I think. I'd say Manx's Shearwater.

Too big for Manx
First thought was Great....but it could just as easily be a oddly-lit preening Cory's

I wouldn't rely too much on size, but I'm far from sur of course.

http://www.birdspix.com/wp-content/uploads/2011/10/Manx-Shearwater-with-Corys-6946b.jpg