Split Willisornis vidua from Willisornis poecilinotus
Proposal (495) to South
American Classification Committee
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.”