I've had an email from Jeff Davies in Australia referring to the first of the shearwaters I saw on 27th April.
"It looks like a young Sooty to my eye.
Bill looks longish.
Outer wing long and tapering as opposed to more paddle shaped in Short-tailed which you undeniably had later in the day. Your bird is in a classic Sooty posture showing nice long tapered wings.
Wing tips flex up on downward stroke.
Underprimary area contrasting darker than coverts.Short-tailed under-primaries are reflective and tend to present pale like the coverts often with little or no tonal difference. Your bird shows the distinctive white blaze of a Sooty contrasting with dark primaries. This combined with the outer long and tapered wing shape is diagnostic. Note how the wing tip on the right side is flexed up, this is also diagnostic and very obvious when watching a bird go close by. When the under-primaries are reflective a little as in your ventral image the greater coverts always seem to stay dark and present as a short narrow arc away from the leading edge of wing. Your bird also shows this.
Young Sootys lack the obvious dark grizzled marks in the primary coverts, having streaks more like a Short-tailed that are not as easily seen from a distance."
I took quite a few photos of this bird, and include them all below, cropped but unedited, in the order taken.
The bird was seen early in the morning in low sunlight. It flew directly across the path of the boat, staying low to the sea surface, flight consisting of glides interspersed with bursts of powerful flapping. In the practically calm sea conditions we normally have, I would say that this flight mode is quite typical of Short-tailed Shearwaters we see here.
I'd love to hear more views on this bird from those familiar with both Short-tailed and Sooty Shearwaters. Please email me or make a comment on this post. Thanks