I'm posting this on behalf of a colleague. This dark shearwater was pulled from a burrow in extreme NW Tasmania, Australia (it died and was subsequently frozen and thawed, hence the poor condition in the photos). The legs & bill are whiter, and the bill shorter than those of Flesh-footed Shearwaters.
It wasn't very fat, but not lean either, and weighed about 380g (many Short-tailed Shearwaters collected from the same colony at the same time weighed 480g). My colleague's opinion after she handled the carcass was that the underwing coverts were lighter than Flesh-foots or Short-tails as well (both of which she's had extensive experience). It also seems far too small to be a Sooty.
Thoughts and comments greatly appreciated.
St. John's, Newfoundland