Proposal (659) to South American Classification Committee
Elevate Xiphorhynchus fuscus atlanticus to species rank
Effect on SACC: This proposal, if passed, would split the Lesser woodcreeper Xiphorhynchus fuscus into two species (X. fuscus and X. atlanticus).
Background: The Lesser Woodcreeper Xiphorhynchus fuscus Vieillot (1818) inhabits the Atlantic forest of Brazil, eastern Paraguay and Argentina (Misiones), from sea level up to about 1200 m.a.s.l. There are four subspecies: atlanticus, brevirostris (also known as pintoi), tenuirostris and the nominal subspecies. Subspecies atlanticus is restricted to northeastern Brazil, to regions north to the Rio São Francisco (states Piauí, Ceará, Rio Grande do Norte, Pernambuco, Alagoas and Sergipe). Specifically, it inhabits the rainforests of the coastal range, and of the isolated tops of humid highlands surrounded by dry forests (Caatinga).
According to a mitochondrial and nuclear genetic study, only the subspecies atlanticus is monophyletic (Cabanne et al., 2008). Also, atlanticus is the only subspecies isolated genetically and geographically. Besides, subspecies atlanticus is considered to differ by song, but there is not published a formal study on it (Cabanne in prep). According to this background, atlanticus is considered a full species by some taxonomic authorities, such as the Brazilian list of birds (Comitê Brasileiro de Registros Ornitológicos, 2014).
Cabanne et al 2014 studied body size and plumage color of populations of X. fuscus and found that atlanticus can be differentiated by plumage (Fig. 3 and 5 of cited paper) and body size (Fig. 6 and 8 of cited paper), which is complemented with the previous genetic results showing that the population is genetically isolated (Cabanne et al., 2008). Subspecies atlanticus is the darkest and most brownish population and the only one presenting plain undertail coverts. The other subspecies have striated undertail covers. In relation to body size, X. fuscus atlanticus represents the population with the largest birds. The other populations have a bill 7.5% to 14% smaller than in atlanticus, as well as wing and tail length 5% to 10% smaller and tarsi 2.5% to 9% smaller than the ones found in atlanticus.
I recommend elevating subspecies atlanticus to species rank. Cabanne et al. (2014) concluded that the subspecies could be considered an independent evolutionary lineage and a full species according to the General Lineage Concept, the Biological concept and the phylogenetic species concept. The population is genetically isolated, and diagnosable by plumage and body size characters.
If passed, the English name of the Xiphorhynchus atlanticus could be Northern Lesser Woodcreeper.
Cabanne GS, Trujillo-Arias N, Calderón L, D’Horta F M, Miyaki CY. 2014. Phenotypic evolution of an Atlantic Forest passerine (Xiphorhynchus fuscus): biogeographic and systematic implications. Biological Journal of the Linnean Society, Early view, DOI:10.1111/bij.12362.
Cabanne GS, d'Horta FM, R. Sari EH, Santos FR, and Miyaki CY. 2008. Nuclear and mitochondrial phylogeography of the Atlantic forest endemic Xiphorhynchus fuscus (Aves: Dendrocolaptidae): biogeography and systematics implications. Molecular Phylogenetics and Evolution 49: 760-773.
Comitê Brasileiro de Registros Ornitológicos (2014) Listas das aves do Brasil. 11ª Edição. Available at <http://www.cbro.org.br>. Accessed: November 15, 2014.
Gustavo Sebastián Cabanne (November 2014)
Comments solicited from Curtis Marantz: “My personal experience with Xiphorhynchus fuscus is relatively limited, but I have seen and heard both X. f. atlanticus and at least one and possibly more of the more southerly occurring populations. I have also seen the earlier paper by Cabanne and I have spoken with him about this subspecies, but I have not read the more recent publication. Based on my experience, I would say that the northern birds do look and sound rather different from the southern birds, and my recollection of the paper on genetic differentiation is that Cabanne did a good job of showing the genetic differentiation of this taxon, which may indeed represent a full species based on the Biological Species Concept. However, I cannot now recall just how different the vocalizations of these birds are from the southern populations, and I would suggest that without a quantitative analysis of the vocalizations, it would be premature to elevate X. f. atlanticus to a full species based on the BSC. If such a vocal analysis is in preparation, I recommend holding off on making any decisions about this split until said analysis has been completed. Moreover, vocal variation is marked in other species of Xiphorhynchus, some of which also have larger repertoires than do many suboscines, so any vocal analysis should include at least moderately large numbers of songs from multiple individuals in each population. At present, the genetic and morphological analyses really only indicate, in my opinion, a well-defined and geographically isolated subspecies, so in the absence of work on interbreeding in a zone of contact a vocal analysis would be an important requirement for making a taxonomic change at the species level.”
Comments from Nores: “NO, for now. I agree with Marantz that is rather a well-defined and geographically isolated subspecies. If such a vocal analysis is in preparation, I hope to see the results before making any decisions about this split.”
Comments from Zimmer: “NO. Let me start by saying that I believe Cabanne is correct in his assertion that atlanticus is deserving of recognition as a species distinct from the rest of the fuscus-group under even the BSC. It differs both vocally and morphologically from all other populations of “Lesser Woodcreepers”. I also believe that a comprehensive vocal analysis will reveal a significant split between nominate fuscus and tenuirostris. However, Curtis Marantz is also correct in pointing out that we still haven’t seen any kind of published, comprehensive vocal analysis of this group, and without that, we are left only with genetic distance and consistent, but minor morphological variation involving allopatric populations. Because the prevailing SACC philosophy has been to require peer-reviewed, published analyses before making proposed changes, then, in the absence of such a published analysis, I feel that I have to vote NO, even though I really feel that Cabanne has it right.”
Comments from Remsen: “NO – Kevin’s comments mirror mine exactly. This seems to be a split that needs one more paper to support it.”
Comments from Robbins: “NO for now. However, that tentative decision is not because of the genetic and morphological data, which do support recognition; however, no vocal data are presented. As I’ve made abundantly clear to this committee, I don’t need to see a summary of the vocal data in print, but I do want those data referenced via online sources so that everyone is looking at the same data set. So, I’m fine with the author and the sponsor of this proposal presenting those via online resources.”
Comments from Areta: “NO until the vocal analysis is published. I have been struck by the vocal differences between birds in Misiones (Argentina, southern fuscus) and those at Ilha Grande (Rio de Janeiro, Brazil, apparently northern fuscus) and I have recorded both taxa extensively. Based on genetic data, it seems like the clade brevirostris-tenuirostris, northern fuscus and southern fuscus might all merit full species status together with atlanticus. Until the taxonomy of the complex is solved, I feel uncomfortable splitting just one taxon based only on plumage and genetic data.”
Comments from Cadena: “NO for now. Let's revisit this once vocal analyses have been completed and published on. We have tons of cases of lowland birds showing marked genetic divergence coupled with phenotypic diagnosability across barriers and we do not treat these as separate species unless it can been shown they also differ in traits relevant to species recognition/mating.”
Comments from Stiles: “NO for now, until the vocal data are published.”
Comments from Stotz: “NO. Will need to see the vocal data, but I think likely there are multiple species here.”