Proposal (495) to South American Classification Committee

Split Willisornis vidua from Willisornis poecilinotus

Effect on South American CL: This proposal would split Willisornis poecilinotus into two species.

Background: Our current relevant SACC Note is as follows:

Pinto (1978) treated lepidonota (with duidae) as a separate species from W. poecilinotus, and Hilty (2003) and Zimmer & Isler (2003) suggested that more than one species was involved; however, see Zimmer (1934d), Willis (1982), and Ridgely & Tudor (1994).  Isler & Whitney (2011) presented evidence that the subspecies vidua merits species rank.  Proposal badly needed.

New Information: Isler and Whitney (2011) concluded that the seven recognized subspecies of Willisornis poecilinotus sorted into two groups (vidua and nigrigula of se. Amazonian Brazil versus the remaining five subspecies) based on diagnostic differences in loudsongs, contact calls, and raspy series, as well as diagnosable plumage characters. Conversely, although the subspecies within each of the two groups were generally readily separable from one another based on plumage characters, within-group vocal differences did not meet the authors’ criteria for diagnosability.

Specifically, loudsongs of vidua and nigrigula were frequency-modulated in an even pattern (such modulation either lacking or erratic in the other populations of Willisornis), creating differences in note shapes as viewed in spectrograms that allowed perfect allocation of loudsongs to the two groups. The differences in sound quality reflected in the spectrograms are also readily apparent in the field to the human ear (Isler and Whitney 2011; KJZ personal observation). Furthermore, vidua and nigrigula share a distinctive contact call (termed a “twitter” by Isler and Whitney) that differs qualitatively and in several quantitative measures from the “psit” contact calls given by the other Willisornis taxa. “Raspy series” vocalizations of vidua and nigrigula also differed consistently from those of the other subspecies.

Based on all of this, Isler and Whitney (2011) recommended that vidua, together with nigrigula, be treated as a single species (vidua has priority) distinct from the remaining 5 Willisornis subspecies. Although vidua and nigrigula differ markedly in plumage characters (male vidua with a whiter throat contrasting with pale-to-medium gray underparts; male nigrigula with a black chin/throat patch; females differ in flank coloration and wing markings) from one another, they form a vocally cohesive group that does not seem to merit further splitting at this time.

Isler and Whitney were also unable to recommend further splitting among the remaining five subspecies of Willisornis, although plumage characters were generally diagnostic, and some vocal characters exhibited only minimal overlap in ranges (but failed to meet their criteria for splitting).

Recommendation: I recommend a YES vote on this proposal. These authors have done their usual thorough job in demonstrating that the proposed species differ unambiguously from one another in multiple vocal characters, easily meeting the rather conservative Isler et al. (1998, 1999) criteria or “vocal yardstick” for splitting. The two groups of Willisornis also differ morphologically from one another, and preliminary molecular data (pers. comm. from J. Bates, cited in Isler and Whitney 2011) suggest that parapatrically distributed populations of W. v. nigrigula and W. p. griseiventris showed 6.8% divergence in two mitochondrial genes on opposite banks of the rio Teles Pires (a headwater tributary of the rio Tapajós).

English name: Isler and Whitney (2011) suggested the English name of “Xingu Scale-backed Antbird” for vidua/nigrigula, while modifying the English name of the remaining populations to “Common Scale-backed Antbird”. The former is derived from the name of the rio Xingú, the major south bank tributary of the Amazon that flows through the center of the range of W. vidua. The latter speaks to the extensive Amazonian/Guianan collective range of the remaining five taxa. As such, I think both names are entirely appropriate. There may be some resistance to the length of these compound names (and I confess to a fairly strong distaste for the modifier “Common” for almost any bird), but I think that realistically, we can’t keep coming up with short, simple names that are also informative. Retention of “Scale-backed Antbird” with different modifiers for the two resultant species conveys information about their relationship to one another.

Literature Cited:

ISLER, M. L., P. R. ISLER, AND B. M. WHITNEY. 1998. Use of vocalizations to establish species limits in antbirds (Passeriformes: Thamnophilidae). Auk 115: 577-590.

ISLER, M. L., P. R. ISLER, AND B. M. WHITNEY. 1999. Species limits in antbirds (Passeriformes: Thamnophilidae): the Myrmotherula surinamensis complex. Auk 116: 83-96.

ISLER, M. L., AND B. M. WHITNEY.  2011.  Species limits in antbirds (Thamnophilidae): the Scale-backed Antbird (Willisornis poecilinotus) complex.  Wilson J. Ornithology 123: 1-14.

Kevin Zimmer, September 2011

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Comments from Stiles: “YES – here too, the evidence favors splitting vidua from poecilinota; the English names proposed seem reasonable as well.”

Comments from Robbins: “YES. I suspect genetic data will reinforce plumage differences and will result in recognition of additional species in this complex.”

Comments from Pacheco: “YES. Um sim baseado num rico e muito bem manejado trabalhado de análise dos repertórios dos táxons.”