'Atoll' Shearwater - Western Pacific Odyssey
Tony Pym
Atoll Shearwater? Like Angus, I’d never heard of Atoll Shearwater, nor seen this name in print.
As already stated, the Little/Audubon’s Shearwater complex is a minefield and the last chapter certainly not yet written. Consider, the taxonomy and nomenclature of those in the North Atlantic; for example, is boydi a race of Macaronesian (as viewed. presently, by the BOU) or of Audubon’s (per Onley and Scofield) or is it a further species? Added to which the AOU still treat Macaronesian (baroli) as a race of Little Shearwater!
And, why was the secondary name North Atlantic Little Shearwater coined when Macaronesian was already well in use? There isn’t a ‘South Atlantic’ Little Shearwater and now that Little is used only for New Zealand/Australasian birds the name only confuses and muddies the water further.
I remember, about fifteen years back, the entire complex consisted of some twenty forms, under the two species, with about eleven being described from the regions of the Indian and Pacific Oceans. The major paper by Jeremy Austin, Vincent Bretagnolle and Eric Pasquet (The Auk, July 2004) redefined the phylogenetic relationship of the small shearwaters and found three clades and suggested fourteen taxa be recognised (and that a number were no longer valid).
Coming back to the Western Pacific Odyssey I see that Tropical Shearwater was logged on 16/4 and then ‘Atoll’ Shearwater on 23/4, implying those aboard think they are not the same species. Also, Angus’s post, quoting Steve Howell, says that the Pacific form, dichrous, ‘realistically is endemic’. For interest, Austin et al, found dichrous (paraphyletic, with other forms) of the Pacific and bailloni of the Indian Ocean to be lineages of a clade; this now called Tropical Shearwater. Their distribution may be allopatric but the genetic results could be interpreted as long-distance expansion, to mean the species originally dispersed from the Indian Ocean out to the Pacific and then back again.
A major problem with species in the Little/Audubon’s grouping is that plumage features used to identify in the past (notably upperpart colour, undertail colour, leg colour) now conflict with the biological research, let alone the DNA results. On top of that there is moult and ageing to consider in the field also.
I would love to hear the differences between these birds at sea. It raises many questions: Is ‘Atoll’ Shearwater different from Tropical Shearwater of the Pacific? Is ‘Atoll’ Shearwater sufficiently different from Indian Ocean birds? Is another Pacific form being seen, for example polynesiae? Maybe a distinct undescribed form is being seen? Quite possibly the fieldwork is showing differences from the laboratory?
Something to ponder over…..
Tony Pym
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