that the Pacific and Indian Ocean subpopulations must have been isolated for a fairly long time, and that no less than three unequivocally distinct subspecies (bailloni, persicus and temptator) occur within the range of Indian Ocean dichrous. On the other hand, the supposed species Mascarene shearwater (P. atrodorsalis) is inseparable morphologically and genetically from bailloni. Clearly, some mechanism blocking gene flow is at work, but what this is exactly remains unknown – though as remarked above, separate breeding seasons seem a reasonable assumption and are tentatively supported by the available field data. In addition, it is entirely mysterious why such a mechanism should apply in the rather limited and ecologically homogeneous north-western Indian Ocean range, but not in the ecologically more diverse and by far larger Pacific range of dichrous. These unresolved problems notwithstanding, this clade – possibly including the preceding one – has been proposed to constitute a separate species, the tropical shearwater or Baillon's shearwater, Puffinus bailloni. Undetermined Bannerman's shearwater, Puffinus lherminieri bannermani Mathews & Iredale, 1915 – breeds on Ogasawara Islands (NW Pacific); ranges throughout the NW Pacific from Japanese waters to the equatorial region. Vagrants recorded from Guam and Rota (Marianas) might be dichrous or bannermani. Puffinus lherminieri gunax Mathews, 1930 – breeds on Banks Islands of Vanuatu (SW Pacific); ranges throughout the SW Pacific between the equatorial region and the Tropic of Capricorn. Might belong in dichrous; vagrants seen off Australia could belong to either taxon. These taxa could not be included in the most recent studies due to lack of material. The case of gunax seems fairly straightforward – as certainly as this can possibly be said in the absence of new data, it belongs to the bailloni clade either as a distinct subspecies, or, more likely, as yet another synonym of dichrous. The case of the more distinct bannermani, the range of which is parapatric to that of the Pacific dichrous, is more complicated. It has for some time been proposed as a distinct species, Bannerman's shearwater (P. bannermani). In the absence of more recent data to investigate this claim, its status continues to be altogether unresolved, though the case for it being at least a distinct subspecies in the bailloni clade seems good. Footnotes References Austin, Jeremy J. (1996): Molecular Phylogenetics of Puffinus Shearwaters: Preliminary Evidence from Mitochondrial Cytochrome b Gene Sequences. Mol. Phylogenet. Evol. 6(1): 77–88. (HTML abstract) Austin, Jeremy J.;