Proposals (#261a, 261b) to South American Classification Committee
Proposal 261a. Split Dysithamnus plumbeus and D. leucostictus
Proposal 261b: Split Dysithamnus tucuyensis from D. plumbeus or D. leucostictus
Proposals: These proposals are (i) to recognise a split reflected in almost all recent field guide literature; (ii) for completeness, to consider a split that has recently been proposed; and (iii) to adopt one of two possible names for one of the "new" species that would result. Like the recent Conopias proposal, no formal analysis directly on topic has ever been presented in a scientific journal. However, the first split is strongly supported by morphological, biogeographical and vocal evidence which have been published in various field guides and CDs. The second split is apparently supported by vocal and biogeographical considerations but less published literature exists on the topic and the differences are not as clear-cut as on the first.
Plumbeous Antvireo D. plumbeus is a lowland Atlantic forest species endemic to Brazil, with a small and fragmented range. It is currently assessed as Vulnerable by BirdLife International (2004). This is of note given BirdLife's move towards convergence with SACC.
Nominate White-streaked or White-spotted Antvireo D. [p.] leucostictus is present in cloud forest on the east slope of the Andes from Peru to Colombia.
Greater D. leucostictus and D. plumbeus have disjunct ranges c. 4000 km apart. Any recent contact is unlikely. The possibility that variations in morphology and voice from localities of sound recordings or specimens (discussed below) could vary clinally in the intervening regions can be discarded.
Venezuelan Antvireo D. [l./p.] tucuyensis is present in the coastal cordillera of Venezuela and has recently been assigned species rank in a major field guide on the basis of its voice and plumage (Hilty 2003) following previous suggestions that this might be warranted (Ridgely & Tudor 1994; Zimmer & Isler 2003). The taxon has an apparently disjunct range, with records of D. leucostictus only in the Amazonian-bordering region of the east slope of the Andes north to in Meta, Colombia (recent range extensions set out in Salaman et al. 2002) and no records of any relative in Norte de Santander, Tamá or Merida regions. D. leucostictus is a forest specialist that is not abundant where found and has a narrow elevational range. The apparent gap in records from Meta to Norte de Santander in Colombia may not be a real one given the lack of mist-netting or other studies in that region (and I have heard of an unpublished sight record in Santander). The lack of any records in the Merida mountains may be more significant.
D. plumbeus and greater D. leucostictus are similar in male plumage, though may differ slightly in the extent of white barring on the wings and shade of black/very dark grey on the underparts. The females, however, look nothing like one another. Female D. plumbeus are uniform plain brown with 2 whitish wingbars and a lighter throat. Female D. leucostictus have slate grey underparts with broad white streaking and a chestnut mantle, wings and crown.
The plumage differences between D. plumbeus and greater D. leucostictus have been discussed in at least two publications: Ridgely & Tudor (1994) in Birds of South America: Suboscines and Zimmer & Isler (2003) in Handbook of the Birds of the World. In the latter case, plumages are illustrated.
Turning to D. [l./p.] tucuyensis, males are similar to nominate D. leucostictus. In females, the streaking on the underparts is broader and less contrasty (see plates in Zimmer & Isler 2003 and Hilty 2003).
Loudsongs of the all three taxa have been published in commercially available recordings and have been described and discussed in at least two publications (Ridgely & Tudor 1994 & Zimmer & Isler 2003). A sonogram of D. leucostictus' call is set out in Whitney (1992). Quoting Zimmer & Isler (2003):
"D. plumbeus: short (4 notes, 1.3 s) series of moderately long whistles (notes longer than spaces between notes), second note at higher pitch than first, 3rd and 4th declining in pitch, first and second notes less intense.
"D. leucostictus: short (6 notes, 1.8 s) easily countable series of strong whistles, pitch falling (except sometimes initial note), first and last notes more intense.
"D. [l./p.] tucuyensis: moderately long (13 notes, 2.7 s) barely countable series of strong whistles, pitch and intensity gradually rising to middle notes, then gradually declining."
English Names (to be considered in separate proposal if one or both of the splits accepted:
Two possible English names exist for D. leucostictus. The historic name is "White-spotted Antvireo" (referred to in e.g. Meyer de Schauensee publications, pre-split). However, Ridgely & Tudor (1994) noted that the female's underparts are streaked, not spotted. They suggested "White-streaked" instead. "White-streaked Antvireo" is probably more widely used in works referred to herein. Some exceptions are Sibely & Monroe (1993) and BirdLife International (2004), who each go for "White-spotted". A Google straw poll also showing 225-98 in favour of "streaked". Given that historical stability arguments are of little relevance for a taxon recently recognised as a species, I recommend "White-streaked" as the better name of the two names.
Both Ridgely & Tudor (1994) and Hilty (2003) suggested "Venezuelan Antvireo" for a split D. tucuyensis, thus with only one name, no proposal is raised on this issue.
Ridgely & Tudor (1994) concluded that D. leucostictus and D. plumbeus should be split as a result of their "wide range disjunction, very different elevations, strikingly different female plumages and very different behaviour and songs". Zimmer & Isler (2003) agreed and the split has also been followed by subsequent BirdLife International publications (various), checklists of Northern South America (Rodner et al. 2000) and Colombia (Salaman et al. 2001), Birds of Ecuador (Ridgely & Greenfield 2001) and a recent range extensions article (Salaman et al. 2002) among others. This split is strongly supported and widely followed.
Evidence for the D. tucuyensis split is less strong than that for the D. leucostictus split. Only Hilty (2003) among recent field guide publications recognises this split, with other publications (e.g. Ridgely & Tudor 1994, Zimmer & Isler 2003) merely noting that it requires further investigation. Having observed and heard both taxa in the field, I suspect Hilty is right. The only question is whether this is one of those splits that the SACC decides it would like to see more evidence on before accepting.
Conservation Implications: A split D. leucostictus renders D. plumbeus Vulnerable. This is one of very few taxonomic treatments where BirdLife International (who recognise the split) has not followed SACC. A split D. tucuyensis would require re-evaluation of each of the other two taxa, both of which have rather small ranges and are largely restricted to forest. Without putting a conservation cart before a taxonomy horse, I note merely that these proposals could have important conservation ramifications.
1. Split D. leucostictus: YES, definitely.
2. Split D. tucuyensis: tentatively in favour based on field experience, published sound recordings and descriptions thereof, but committee members may consider that a more detailed study (involving e.g. biometrics, molecular work) may be prudent before making a change. Yes is to accept the split; no to reject it.
All on SACC references site.
Thomas Donegan, January 2007.
Comments from Zimmer: "A qualified "NO". I think there is no question that D. plumbeus is specifically distinct from the other two forms, regardless of the species concept employed. Vocal and morphological differences, combined with a humongous range disjunction all point to plumbeus as being a separate beast, and indeed, that is how Mort Isler and I treated it in HBW Volume 8. Conservation considerations (as suggested by Thomas Donegan) also argue for this change being made sooner rather than later, since plumbeus is clearly a rare and threatened bird. So, I could go along with that split (261a). However, the case for splitting leucostictus and tucuyensis from one another is much less clear-cut, and really does require a thorough, quantitative analysis. Such an analysis is not only under way, but is well-under way (Isler & Isler et al.), and should be completed and submitted for publication soon. I would suggest that we hold off on this proposal until this analysis is completed. In the case of plumbeus, the analysis will confirm what has long been suspected; in the case of leucostictus and tucuyensis, it is really required to be certain of which way to go."
Comments from Remsen: NO. With the formal analysis indicated by Kevin underway, let's wait."
Comments from Stiles: (261a) "YES. The evidence favoring the split of leucostictus from plumbeus is much stronger than that for continuing to lump them, despite the lack of a specific quantitative analysis. A) the huge range disjunction is matched by several other taxa now (if not always) split, like Baryphthengus, B) the vocal evidence is quite convincing - at least they certainly sound diffeent to me, and C) the phenomenon of heterogyny (females much more different than males) occurs in several other thamnophiline genera, notably Cercomacra - in the latter, some of the species involved are sympatric. These two were split by Chapman (1926) on the basis of the different females, but he noted the great similarity othe males, which apparently was the criterion used by Hellmayr to lump them; in this case, I prefer to follow Chapman. I also agree with "White-streaked" as an English name."
Comments from Stiles: 261b. "NO, for now. The differences in female plumages are much less pronounced, the voices are less different (but certainly not alike) - here a more detailed study would be nice."
Comments from Nores: (261a) "YES. Pienso que hay sobradas razones para considerarlos especies distintas. El plumaje de la hembra y el canto son importantes y el gran gap entre los rangos es para mi definitivo. No puedo pensar que una "understory species" pueda tener una subspecies separada 4000 km."
Comments from Nores: (261b) "NO. Aunque el caso es algo parecido al anterior, las diferencias morfológicas y la aislación de los rangos no son tan marcados. De todos modos, sería imprtante ver si las diferencias en los los cantos indicada por Donegan son suficiente para considerarlas especies distintas."
Comments from Cadena: "261a, 261b. NO for now. The relevant data have not been published, but they will be soon. Let's wait for the publication of the analyses described by Kevin."
Comments from Robbins: "NO, for reasons outlined by Kevin, it seems prudent to hold off on making any changes at the moment given that a manuscript is eminent."
Additional comments from Stiles: "As per Daniel's comment - I am willing to change my vote to a temporary "no" if a manuscript on these birds is indeed in the works and could be at least accepted by the time we go to print."
Additional comments from Donegan: "I was unaware
of the forthcoming publication mentioned
by Kevin Zimmer above. However, I do not think that this changes anything as regards proposal "a". Few,
if any, authors other than SACC treat D. leucostictus and D. plumbeus as lumped. As Gary Stiles has pointed
out, the split/lump status of these species has been debated for the best part of 80 years and has been resolved in the last 15 or so with vocal and biogeographical evidence in favour of the split. Giving the SACC current treatment for this/these species some kind of "holy cow" status seems strange when it is by far the exception to all other recent ornithological literature. Further, we have a strong indication that a forthcoming article will "confirm what has long been suspected" on this issue. I am not sure how necessary it is for anyone to "confirm" that this split is a good one, given that the evidence in favour has been published in textbooks and commercially available sound recordings for some years, is very strong and is widely followed. A publication is a publication, whether a book or a journal - and publications in journals, such as Chapman's publication (which was published in a journal series) have included discussion of this issue in favour of a split. Further, Kevin Zimmer, in suggesting a "no" vote here (that others have followed) is going against his own treatment in "Handbook of the Birds of the World" and his own approach in the Conopias proposal. The evidence for this split is stronger than that for the Conopias species, as lack of sampling of certain regions cannot be raised as an objection. Finally, these are two range-restricted species, one of which is threatened. Downgrading one of them to subspecies rank (the effect of a no vote) will cause BirdLife to change their treatment - and could render the threatened Brazilian
taxon and its habitat less of a conservation priority. I fail to see anything positive or sensible that would be achieved here by a "no" vote for proposal A and urge those who have voted to reconsider. On B, however, the proposal to wait for the published research to come out seems reasonable. Proposal B, as noted above, was raised for completeness only (in response to accusations of other proposals being "piecemeal"). If A should be rejected due to *not* involving a piecemeal approach and bundling by committee members of votes with B, this could send out a negative message to persons authoring future proposals."
Comments from Jaramillo: "261a - YES. Ample available, published data,
analysis and opinions exist that all suggest these two should
be divided. It also makes a great deal of biogeographic sense
to me. As far as I can tell, there really is no dissenting opinion
out there to keep these under one species.
261b - NO, let's wait for the analysis."