Proposal (929) to South American Classification Committee

Note from Remsen: Rodrigo Barrios and Alvaro would like to propose adding Pterodroma gouldi to the SACC list based on a reidentified photo from Chile, but we currently treat gouldi as a subspecies of P. macroptera. This is Terry Chesser’s proposal to NACC to split gouldi from macroptera, which passed, and so I am submitting to SACC with his permission.

Treat Pterodroma gouldi as a separate species from P. macroptera

Background:

The Great-winged Petrel Pterodroma macroptera is a relatively large, dark petrel that we currently treat as a single species with two subspecies: the nominate subspecies breeds on islands in the southern Atlantic and Indian oceans, and subspecies gouldi breeds exclusively on islands off the North Island of New Zealand. The latter was described by Hutton in 1869 as Aestrelata gouldi, the type specimen having been collected by Gould off Tasmania. Subspecies gouldi differs from the all-dark nominate form in the contrasting pale gray feathers on its forehead, chin, and throat, which give it the English name Gray-faced Petrel. The new species was merged into P. macroptera by Mathews and Iredale (1913) and was considered a subspecies of macroptera by most twentieth century references (e.g., Peters 1931, 1979; Sibley and Monroe 1990). However, some recent sources (e.g., Onley and Scofield 2007, Howell 2012) have once again split P. gouldi from P. macroptera, based largely on appearance, range, and vocalizations. The species appears on the AOS Checklist based on a small number of records of gouldi off the coast of California (Banks et al. 2004).

New Information:

Wood et al. (2017) conducted a comprehensive study, including analyses of plumage, morphometrics, osteology, mtDNA, vocalizations, parasites, and behavior, of the taxonomic status of the Gray-faced Petrel. The genetic analyses, which were performed using BEAST, provided the surprising result that Great-winged Petrel P. macroptera is sister to White-headed Petrel P. lessonii rather than to Gray-faced Petrel P. gouldi. This was indicated in analyses of partial sequences of CO1 that included nine taxa of Pterodroma:

and in analyses of complete sequences of cytochrome-b that included 24 species of Pterodroma (only the relevant part of the tree is shown):

Other than the sister relationship of lessonii and macroptera, relationships in this part of the tree are poorly resolved, but the phylogeny suggests that taxa other than lessonii (e.g., incerta and magentae) may also be more closely related to macroptera than is gouldi. Although P. lessonii was not included in the networks, mitochondrial differences between gouldi and macroptera were also illustrated using haplotype networks of CO1 (7.A below) and cytochrome-b (7.B):

Differences in vocalizations were also evident in both sonograms and in analyses of individual components of their vocalizations. Sample sizes for macroptera and especially lessonii were somewhat small (n=8 and n=4, respectively), but the analyses of Wood et al. (below in their Table 1) indicated that vocalizations of macroptera and lessonii were much more similar to each other than either was to gouldi.

Information from the scientific literature also revealed differences in life history characteristics between macroptera and gouldi: macroptera lays eggs from mid-May to early June, with hatching in mid-July, whereas gouldi lays from mid-June to late July and hatches in August-September, differences that hold among birds breeding at the same latitudes.

Differences in plumage between the dark macroptera/gouldi and the White-headed Petrel P. lessonii, which has white underparts as well as a white head, are obvious (see below for photos of specimens). However, in at least some morphometric features, gouldi and lessonii were much more similar to each other than to macroptera (see figure below), and the differences in plumage between macroptera and gouldi exceed those between some other species of Pterodroma (Howell 2012).

Ventral and side views of typical specimens of (from left to right) P. macroptera macroptera, P. macroptera gouldi, and P. lessonii, from Wood et al. (2017).

Recommendation:

I recommend that we split Gray-faced Petrel P. gouldi from Great-winged Petrel P. macroptera. Several lines of evidence indicate that these taxa are not as closely related as previously thought, but instead have been considered conspecific largely based on similarities in plumage. As Wood et al. (2017) noted, some of this evidence has shortcomings when taken individually (e.g., only mtDNA was sequenced for the genetic study), but cumulatively the data are reasonably robust.

Despite the plumage similarities, numerous characters separate these species, including genetics, vocalizations, and life history. The genetic analyses, although restricted to mtDNA, indicate that the White-headed Petrel P. lessonii is the sister taxon to P. macroptera and that P. gouldi may or may not be sister to the clade of these two species. Vocalizations are important in mate recognition in petrels (McKown 2008), and Wood et al. (2017) suggested that the observed differences are sufficient to prevent interbreeding if these taxa were sympatric. Moreover, morphological differences exceed those between some other species of Pterodroma, and phenology of breeding differs between the two taxa, even at the same latitudes.

This proposal would remove P. macroptera from the NACC checklist and substitute P. gouldi. The English name Gray-faced Petrel (or Grey-faced Petrel) is in general usage for P. gouldi, and I recommend that we adopt this name.

References:

Banks, R. C., C. Cicero, J. L. Dunn, A. W. Kratter, P. C. Rasmussen, J. V. Remsen, Jr., J. D. Rising, and D. F. Stotz. 2004. Forty-fifth supplement to the American Ornithologists’ Union Check-list of North American Birds. Auk 121: 985-995.

Howell, S. N. G. 2012. Petrels, albatrosses, and storm-petrels of North America: a photographic guide. Princeton Univ. Press, Princeton, NJ.

Mathews G. M., and T. Iredale. 1913. A reference list of the birds of New Zealand: Part 1. Ibis 55: 201–262.

McKown, M. M. 2008. Acoustic communication in colonial seabirds: individual, sexual, and species-specific variation in acoustic signals of Pterodroma petrels. Unpublished Ph.D. thesis, Univ. North Carolina, Chapel Hill.

Onley D., and P. Scofield. 2007. Albatrosses, petrels and shearwaters of the world. London: Christopher Helm.

Sibley, C. G., and B. L. Monroe. 1990. Distribution and taxonomy of birds of the world. Yale Univ. Press, New Haven, CT.

Wood, J. R., H. A. Lawrence, R. P. Scofield, G. A. Taylor, P. O. Lyver, and D. M. Gleeson. 2017. Morphological, behavioural, and genetic evidence supports reinstatement of full species status for the grey-faced petrel, Pterodroma macroptera gouldi (Procellariiformes: Procellariidae). Zoological Journal of the Linnaean Society 179: 201-216.

Terry Chesser, November 2021

Comments from Areta: “YES. All the datasets unambiguously argue in favor of recognizing P. gouldi as a different species from P. macroptera.”

Comments from Lane: “YES. Not a particularly surprising result, and I expect we'll be seeing many more tubenose splits as we get more phylogenetic and field data on them.”

Comments from Pacheco: “YES. The data gathered by Wood et al. (2017) undoubtedly support the proposal. This comprehensive analysis revealed that Pterodroma macroptera is not even a sister species of P. gouldi.”

Comments from Bonaccorso: “YES. Together, the (genetic, morphological, and vocal) evidence is convincing in separating Pterodroma gouldi from P. macroptera. In my view, it also nicely explains the geographic overlap among both species in eastern Australia (if the BOW maps are accurate).”

Comments from Claramunt: “YES.”

Comments from Zimmer: “YES. Differences in vocalizations and phenology of breeding would seem to be much more important to assortative mating (or the lack thereof) than minor plumage differences in this group of birds. The sum of available evidence all points to treating these two taxa as separate species.”

Comments from Remsen: “YES. All data, especially voice, favor species rank and clearly place burden-of-proof on subspecies rank.”

Comments from Robbins: “YES.”

Comments from Stiles: “YES to this split.”