There is currently (Sept, 2014) a proposal before the IOC to promote Little Shearwater subspecies elegans to full species status as Subantarctic Shearwater, Puffinus elegans.*
Little Shearwater subspecies assimilis has the dark grey of the head finishing above the eye while elegans has the dark grey coming down just below the eye.
The poor light and the angle of view has made the black under the bird's tail seem much more prominent than it should be.
*Gill, F & Donsker, D (Eds). (2014). IOC World Bird List (v 4.3). doi : 10.14344/IOC.ML.4.3.