Proposal (809) to South American Classification Committee

Recognize Xiphorhynchus atlanticus as a separate species from Xiphorhynchus fuscus

Effect on SACC: This proposal, if passed, would split the Lesser Woodcreeper Xiphorhynchus fuscus into two species, X. fuscus and X. atlanticus.

Background: This is the second proposal to treat Xiphorhynchus atlanticus as a species. The earlier proposal 659 did not pass because, as explicitly stated by the committee members, it was not supported by a vocal analysis. This deficiency has now been corrected.

To recap the earlier proposal, 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, tenuirostris and the nominate. Subspecies atlanticus was described in 1916 by Cory based on one specimen from Serra Baturite, Ceará state, Brazil (Cory, 1916). Later, Zimmer (1947) checked 4 other specimens of this subspecies from Pernambuco state in Brazil (3 males and 1 female). Both Cory (1916) and Zimmer (1947) described differences in color and morphology in agreement with those quantified by Cabanne et al. (2014). The form atlanticus is restricted to northeastern Brazil, north of the Rio São Francisco, in the states of Piauí, Ceará, Rio Grande do Norte, Pernambuco, Alagoas, Sergipe and Paraíba. It inhabits the rain forests of the coastal range and the isolated tops of humid highlands surrounded by dry forests (caatinga). Cabanne et al. 2008 showed that atlanticus is the only subspecies isolated both genetically and geographically. Cabanne et al. (2014) showed that body size and plumage differentiated atlanticus from the other subspecies of X. fuscus.

New information: Garcia et al. (2017) analyzed the songs of X. fuscus. They detected two distinct songs, song I and song II, and three distinct types of song I, types A, B and C. They found that individuals of X. fuscus produce both song I and song II, but only one type of song I. They therefore focused their analyses on song I. All individuals assigned to song I type A were recorded in northeastern Brazil, in the same area as the atlanticus lineage and they concluded that X. fuscus atlanticus can be differentiated by its vocalizations as well as by plumage and body size. The authors did not find sufficient evidence to raise the other subspecies or lineages of X. fuscus to the level of species.

Recommendation: We recommend a YES vote to split X. atlanticus and X. fuscus as two separate species based on the combined genetic, morphological and vocal evidence. While it would be also ideal to have experimental evidence of differential responses to playback, we stress the importance of re-evaluating the status of the form atlanticus. As this form inhabits the most endangered portion of the Atlantic forest, this decision would have important conservation implications and would require a re-evaluation of the conservation status of this population.

Literature cited:

Cabanne, G. S., d’Horta, F. M., Sari, E. H. R., Santos, F. R. and Miyaki, C. Y. 2008. Nuclear and mitochondrial phylogeography of the Atlantic forest endemic Xiphorhynchus fuscus (Aves: Dendrocolaptidae): Biogeography and systematics implications. Molecular Phylogenetics and Evolution 49 (2008) 760–773.

Cabanne, G. S., Trujillo-Arias, N., Calderón, L., D’Horta, F. M., Miyaki, C, Y. 2014. Phenotypic evolution of an Atlantic Forest passerine (Xiphorhynchus fuscus): biogeographic and systematic implications. Biological Journal of the Linnean Society, 113, 1047–1066., DOI:10.1111/bij.12362.

Cory, C. B. 1916. Descriptions of Apparently New South American Birds. Ornithological Series Vol. 1, No. 10. Field Museum of Natural History, Chicago.

García, N. C., Naka, L. N. and Cabanne, G. S. Vocal variation in relation to genetic structure in an Atlantic forest woodcreeper (Xiphorhynchus fuscus): evolutionary and taxonomic implications. J. Ornithology 159: 379–388.

Zimmer, J. T. 1947. New birds from Pernambuco, Brazil. Proceedings of the Biological Society of Washington 60: 99-106.

Gustavo S. Cabanne, Natalia García and Jeremy Minns, November 2018

Note from Remsen: We will need a separate proposal on English names if the split passes.

Comments from Stiles: “YES. the convergence of genetic, morphological and vocal evidence supports species status for atlanticus. However, a couple of things not mentioned in the proposal (possibly mentioned in the García et al. paper) would make the case more complete: is song type 1A the only type given by atlanticus, or does it also give types 1B and1 C - in other words, are types 1B and 1C exclusive to the other taxa? Could the different song types have different functions, particularly with respect to mate selection vs. territoriality?”

Comments from Claramunt: “YES. The new data show that atlanticus has a type 1 song that is different (ascending monotonically in pitch) from type 1 songs of the other forms. Genetically, atlanticus represents a separate mitochondrial linage and possesses unique nuclear variants (BF5 intron), both suggesting absence of gene flow between these two forms (Cabanne et al. 2008). It is also 100% diagnosable from fuscus in plumage (Cabanne et al. 2014). Regarding potential reproductive isolation, the clear-cut differences in loud-song 1 can function as species recognition/discrimination signals that ensure reproductive isolation. This is sufficient evidence to consider atlanticus as a separate species.”

Comments from Zimmer: “YES. The addition of a published vocal analysis, quantifying vocal differences that were pretty obvious to those who know the taxa involved in life, seals the deal for me, particularly when added to the morphological and genetic data, and ecological and biogeographic considerations.”

Comments from Robbins: “YES. The combination of plumage, vocal, and limited molecular data support treating atlanticus as a species.”

Comments from Stotz: “YES. Based on vocal information, I now favor recognition of Xiphorhynchus atlanticus.”

Comments from Pacheco: “YES. Evidence to support this proposal was increased with the recent analysis by Garcia et al. (2018).”