Treat Herpsilochmus frater as a separate species from Herpsilochmus rufimarginatus

Proposal (870) to South American Classification Committee

Treat Herpsilochmus frater as a separate species from Herpsilochmus rufimarginatus

Part A. Effect on SACC list: If adopted, this proposal would elevate Herpsilochmus frater to species rank as a separate species from Herpsilochmus rufimarginatus (monotypic).

Background: Herpsilochmus rufimarginatus was described by Temminck in 1822 (type locality Rio de Janeiro, Brazil). Subsequently more taxa were described: scapularis (Wied, 1931, Bahia, Brazil), frater (Sclater, 1880, Sarayacu, Ecuador) and exiguus (Nelson, 1912, Cana, Panama). Cory and Hellmayr (1924) assigned them to the same species H. rufimarginatus but considered scapularis junior synonym of nominate. Later, Peters (1951), however, considered scapularis a valid taxon, and this treatment with 4 subspecies was repeated by Zimmer & Isler (2003).

As for distinctiveness of the various taxa, Zimmer & Isler (2003) described some morphological and vocal differences without quantification and suggested that more than one species may be involved.

New information:

Phenotypic differences

1. Marcelo da Silva (2013) investigated in detail the morphology and voice of the 3 Brazilian taxa. His findings are in his Master thesis; unfortunately, no follow-up peer-reviewed paper was published.

The main results are copied here:

a. rufimarginatus is morphologically the most distinctive taxon

c. rufimarginatus is vocally the most distinctive taxon

(‘Erro padrao’ is Standard error, not SD!)

Limited unspecified playback experiments were also carried out, in which playing rufimarginatus loudsong in NE Brazil did not illicit response of that population.

2. Independently, Boesman (2016) made a brief analysis of all 4 taxa (including also exiguus). He used in part different sound parameters, and also concluded that rufimarginatus was vocally clearly standing out vs. the other taxa (with measurements indicating several non-overlapping ranges).

3. In a vivid discussion on xeno-canto (https://www.xeno-canto.org/forum/topic/5265 ), involving Dan Lane, Jeremy Minns and myself, there was a general consensus that rufimarginatus was vocally the most distinct taxon.

4. A comparison of calls has not been performed, but seems to be quite complex at first sight, e.g. taxon frater has at least 4 different call types, one of which is rarely heard (and possibly not even over its entire range) but quite similar (not identical) to the main call of rufimarginatus. A large set of recordings of call notes would thus be required, not only to document the full vocal array for every taxon and evaluate (possibly subtle) differences, but also to determine relative frequency for every call type (without even touching the topic of respective functions…).

5. The vocal group identified as rufimarginatus occurs along the Atlantic side from Paraguay and Argentina in the south to Bahia in the north (the most northerly sound recording presently on XC being just north of Salvador), whereas the population north of the rio Sao Francisco was assumed to be scapularis.

Taxonomic names

1. Marcelo da Silva (2013) zoomed in on the specific case of scapularis. The type locality ‘Bahia’ is unprecise, but in any case, must have been a locality south of the rio Sao Francisco, and (given there is uniformity in morphology and voice with birds further south) in fact had been named earlier rufimarginatus; thus he considered scapularis a junior synonym of rufimarginatus. Da Silva, therefore. suggested to redefine a holotype for the northern population occurring from Alagoas to Rio Grande do Norte, but he did not name this taxon (p. 84).

2. The XC discussion mentioned above also mainly focussed on this topic, reaching a similar conclusion: scapularis is a junior synonym of rufimarginatus.

Discussion:

The taxon rufimarginatus is thus readily identifiable by ear (loudsong), differing significantly in a variety of sound parameters. It is also morphologically the most distinct taxon. For the sake of uniformity, it would have been more transparent if the Isler criteria had been applied for this member of the antbird family, as 3 significant sound parameters are considered a yardstick for species level (Isler 1998). Nevertheless, this slightly different approach also clearly illustrates the vocal distinctiveness of this taxon:

Clinal variation is not an issue here; comparing the most northerly loudsong available on XC (XC482426) with the most southerly of the NE Brazil population (XC80216) shows the same vocal break.

No genetic data are presented, but this is not different from the majority of taxonomic changes in the antbird family during the last two decades, given their voice is innate and very stereotypical, allowing clear-cut assessments based on voice. Geographically isolated by the rio Sao Francisco, nominate rufimarginatus can be considered an allopatric population, and thus there is hardly any chance of contact with other populations. Genetic divergence is to be expected, independent of the reproductive barrier created by vocal difference. Distance to the Amazonian frater population is even larger.

For the sake of completeness: although the population in extreme NE Brazil was clearly less different from frater, da Silva also suggested to elevate this taxon to species rank. This is clearly another topic, not in the least because this would definitely require the description of a new taxon. Meanwhile, the best option is likely to include this population in the taxon frater, awaiting further investigation.

Part B. English name: As for the English name, del Hoyo & Collar (2016) used the names Northern and Southern Rufous-winged Antwren (albeit with incorrect ranges for both species and without solving the issue of scapularis). Given that rufimarginatus occurs further north than they assumed, this North/South distinction is less convincing but still a viable option (and more accurate than calling them eastern/western). Keeping ‘Rufous-winged Antwren’ in the name is very meaningful, as they are the only Herpsilochmus species with rufous in the wing, a genus which otherwise shows very few obvious field characters. Maintaining ‘Rufous-winged Antwren’ for only one of them would only cause confusion (old vs new treatment).

Recommendation:

A. Treat Herpsilochmus frater (including subspecies exiguus) as separate species from Herpsilochmus rufimarginatus (monotypic). (The name scapularis becomes invalid.)

B. English name: Southern Rufous-winged Antwren (H. rufimarginatus) and Northern Rufous-winged Antwren (H. frater) (if a NO vote is given, alternative naming is required)

Literature cited

Boesman, P. (2016). Notes on the vocalizations of Rufous-winged Antwren (Herpsilochmus rufimarginatus). HBW Alive Ornithological Note 50. In: Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. https://static.birdsoftheworld.org/on50_rufous-winged_antwren.pdf

da Silva, M. (2013). Taxonomia e Biogeografia da especie politípica Herpsilochmus rufimarginatus (Temminck, 1822) (Aves:Thamnophilidae). https://repositorio.ufrn.br/jspui/bitstream/123456789/18132/1/MarceloS_DISSERT.pdf

del Hoyo, J., Collar, N.J. (2016). HBW and BirdLife International illustrated checklist of the birds of the world. Volume 2: Passerines. Lynx Edicions, Barcelona.

Isler, M., Isler, P. & Whitney, B. (1998). Use of vocalizations to establish species limits in antbirds (Passeriformes: Thamnophilidae). Auk 115:577-590.

Zimmer, K., Isler, M.L. (2003). Rufous-winged Antwren (Herpsilochmus rufimarginatus). In: del Hoyo, J., Elliott, A., Christie, D.A. (eds.). Handbook of the Birds of the World Vol. 8. Broadbills to Tapaculos. Lynx Edicions, Barcelona.

Peter Boesman, July 2020

Comments from Stiles: “YES on the split. NO on Northern vs. Southern: too much ambiguity here. I'd propose Atlantic vs. Western for rufimarginatus and frater-exiguus, respectively. The distribution of rufimarginatus (as described: it would be nice to have a range map!) seems to be characteristic of the Atlantic-forest species of Brazil, whereas frater-exiguus extends westward through Venezuela and Colombia to the Darien in Panama as well as into Amazonia.”

Comments from Robbins: “YES. After listening to multiple cuts of song of these, I vote yes to recognize frater as a species. It would be nice to have a genetic data set for this clade, but the differences in song of frater vs. nominate are so striking that there is no need to wait for those data.”

Comments from Rafael Lima: “I would like to comment about the English names and provide a map to help with Proposal 870 (Herpsilochmus rufimarginatus complex).

“I made a map using eBird points to illustrate the issue. The birds of the "Amazon Group" are green and the birds of the "Atlantic Group" are red. Note that the birds north of the São Francisco River (Pernambuco Center of Endemism) belong to the "Amazonian Group", so Stiles's suggestion of the English names Atlantic vs. Western is not a good idea. I agree with the names suggested by Boesman.

“The other map I made with the IUCN shapefile (the same one used by HBW Alive). Note that (as Peter has already noticed), when HBW Alive split two taxa (based on Boesman 2016), they made a mistake on the map. Since the catalog of Olivério Pinto (1978), the name "H. r. scapularis" has been attributed simultaneously to the population of Bahia (south of the São Francisco River) and the population of Pernambuco Endemism Center (north of the São Francisco River). This misinformation was followed by the printed HBW volume and is still in Birds of the World. The taxon "scapularis" really caused confusion in the literature, because it was assigned to completely different populations (north and south of the São Francisco River).”

Comments from Areta: “YES. The work by Silva is convincing, and the distribution of vocal types is clear. At first hear, I agree with Dan Lane´s comments that the population from Alagoas-Pernambuco seems to belong to frater and not to a new species, but this will need to be properly published before we can make any decision. For the time being, it seems more reasonable to consider them as part of frater.

“Regarding the common English names, I don´t understand the discussion of Eastern-Western vs. Southern-Northern. Both species have overlapping longitudes and latitudes (as Rafael´s map clearly shows), so from that perspective neither is great (and it would make it complicated in the event of more splits). Also, these are among the most boring possible names! Since vocalizations were key for the split, I would suggest a reference to their songs might be better. Something along the lines of Churring Rufous-winged Antwren (frater) and Piping Rufous-winged Antwren (rufimarginatus). I admit I don´t like these long names in any manner, but if Rufous-winged has to stay, then a reference to a feature of the birds and not to their ranges seems better.”

Comments solicited from Mort Isler: “I recommend a YES vote because of the clear distinctions between songs of frater (including exiguus and "scapularis" north of the R. São Francisco) and rufimarginatus (including "scapularis" south of the R. São Francisco). I say that with the hope that future proposals will be better supported.

“Most bothersome, I could not identify the locations of the recordings of scapularis used in Silva's analysis. I could not find yellow dots representing scapularis on Figure 9, and the only list of recording locations (Appendix 2) puts them in his recommended taxa (including the unsubstantiated proposal for a new species). The introduction provides the range of scapularis as Rio Grande do Norte to Minas Gerais, but based on the vocal data, this could not be the scapularis used in the analysis. I have assumed in making my recommendation that scapularis used in the analysis was limited to locations north of the R. São Francisco. My Portuguese has declined with age, so I apologize if I missed it, but delineations of study populations should include recording locations.

“I appreciate the clarity of Peter Boesman's notes for HBW Alive, and I understand that they were only submitted as supporting data, but they are insufficient for making taxonomic decisions for multiple reasons including small sample size, lack of locational data, and absence of distributional data. I only mention this as a concern that others may think the information sufficient.

“I am sad that a more complete analysis of the H. rufimarginatus complex was not available. Peter expressed the same concern in his proposal regarding the absence of calls of the populations analyzed, and it obviously would have been desirable that the entire complex had been considered.

“I have read the proposals for English names, and I hope that any available molecular phylogenies will be consulted before "Rufous-winged" is used in constructing names. The songs (and possibly the calls) differ to an extent that the assumption that frater and rufimarginatus are sister species should be confirmed.”

Comments from Pacheco: “YES. The vocal repertoire of the populations north of the São Francisco River are those of the frater/Amazonian pattern, whereas to the south of the São Francisco River - including all of Bahia (therefore involving "scapularis") - it is possible to hear something identical to that sung in the typical range of H. rufimarginatus (Rio de Janeiro). Rafael did a good job of clarifying where this correct break is.”

Comments from Claramunt: “YES. The evidence clearly points to species-level taxa.”

Additional comments from Areta: “After reading Mort´s comments, and having myself proposed some preliminary alternatives, I think that keeping Rufous-winged for the nominate, and finding a new name for frater would be desirable. I propose Rusty-winged for frater, and Rufous-winged for rufimarginatus. Seems to be the less disruptive option, as one stays the same and the other one would adopt a new name bearing resemblance to its previous name. Alternatively, if both names must change, I would not use "Rufous-winged" as a common theme.

”A final note: I also agree in that Boesman´s notes are good to have an overview of the situation, but the lack of precise catalogue numbers, geographic data, date of recording, and other missing data, make them insufficient to inform taxonomic decisions per se.”

Comments from Zimmer: “YES. The vocal differences between nominate rufimarginatus and the remaining taxa in the complex are pretty obvious to anyone with comparative field experience, so this one has been begging for attention for some time. Mort Isler and I mentioned (HBW Volume 8, 2003) the likelihood that more than one species was nested within rufimarginatus, but in the absence of a comprehensive analysis encompassing the entire complex, we didn’t want to get out over our skies. I might take this opportunity to second Mort’s comments on this Proposal, and note that we still don’t have a comprehensive analysis for the entire group, nor even one that takes into account the various calls. In spite of this, I think the distinctions between the loudsongs of rufimarginatus relative to frater are great enough, particularly taking into account the biometric differences, that we can at least advance the ball downfield by making this one change, and then hope for a more comprehensive analysis providing resolution regarding taxon-limits in the rest of the group, as well as a molecular-based phylogeny to resolve the relationships of the various taxa not only to one another, but also to other species within Herpsilochmus. In the absence of such analyses, it’s worth noting, as some people have already commented, that populations from NE Brazil north of the rio São Francisco are clearly closer vocally to frater than they are to all populations south of the São Francisco. So, pending a comprehensive analysis of the entire complex, the north of the São Francisco population should, provisionally, be placed with frater, whereas populations from south of the São Francisco should be placed with nominate rufimarginatus. (B) “NO” to the proposed English names of “Northern” and “Southern” modifying the group name of Rufous-winged Antwren. Until the taxon-limits are sorted out for the remainder of the group, we are left with the reality that we could be looking at a two-species treatment (rufimarginatus versus frater + exiguus + “scapularis” north of the São Francisco). If things shake out that way, then, as Nacho notes, both species would have ranges that overlap in latitude and longitude, negating the utility of “Northern/Southern” and “Eastern/Atlantic versus Western”. The quality of the songs is the most obvious difference between rufimarginatus and everything else in the complex, and thus, I find Nacho’s suggestion of “Churring Rufous-winged Antwren” (for frater/exiguous/northern “scapularis”) and “Piping Rufous-winged Antwren” (for rufimarginatus) compelling, despite the length and awkwardness of the names. Of course, as Mort has pointed out, we can’t assume that rufimarginatus is sister to frater (sensu lato) just because they both have rufous in the wings. It could prove more closely related to one of the other Herpsilochmus species found in Eastern or South-Central Brazil, in which case we would ultimately be dropping the group name of “Rufous-winged Antwren” and could just go with “Piping Antwren” and “Churring Antwren”. We could also end up in a scenario wherein the complex proves to be a monophyletic group, but either exiguus or northern “scapularis” is shown to merit splitting from frater. In that case (3 species), names describing the voices would not work so well, and we would probably need to revert to English names descriptive of the range (e.g. “Western Rufous-winged” for exiguus; “Amazonian Rufous-winged” for frater; “Sooretama Rufous-winged” for rufimarginatus). There are lots of moving parts here, and in the absence of knowing how the taxonomic dust will settle, I would suggest retaining the compound group name, and using the modifiers suggested by Nacho (Piping and Churring).”

Comments by Lane: “YES. The voices of these two groups are worlds apart (by Herpsilochmus standards, anyway), and I think a split is warranted. Also, I am glad that the proper names are used here! As Peter says, the case for placing the name scapularis under rufimarginatus here, and using “frater” for birds in NE Brazil, is hashed out in da Silva’s 2013 dissertation, the Xeno-canto forum here <https://www.xeno-canto.org/forum/topic/5265> and in the comments and map by Rafael Lima above. Thus, even though there has been a mistaken tendency for much previous literature (e.g., HBW) to use “scapularis” for NE Brazilian birds, the name belongs to those in Bahia, not to those farther north. Therefore, frater is the oldest name for the population with the song type sung by NE Brazilian birds, and it is thus the correct species name for the daughter species once these two groups of taxa are separated. As for English names, I think a separate proposal will need to be drafted to address them.”

Comments from Jaramillo: “YES – Pretty interesting, I had no idea that this separation existed. Weirdly enough, this was the first antwren I ever witnessed in my life, Misiones, Argentina.

“NO on English names, but I am very keen on a yes to the Churring and Piping. I don’t think there is a need to maintain the “rufous-winged” but I would be fine if this is a prerequisite from other committee members.”

Comments from Schulenberg: “B. NO. The recent Harvey et al. paper in Science (Harvey et many al., 2020, The evolution of a tropical biodiversity hotspot, Science 370: 1343-1348, https:/doi.org/10.1126/science.aaz6970) seems to make clear (Figure 1 - if you can read it) that frater (represented by two samples, from Panama and Amazonas, Brazil) and rufimarginatus (also two samples) are sister species. Note, however, that in Column G, of their supplementary table listing the specimens sampled, they identify a specimen from Minas Gerais as scapularis - apparently their name for what SACC refers to as frater - but by location I assume this is a nominate rufimarginatus. or, to put it another way, since the Minas Gerais sample is sister to their sample of undoubted rufimarginatus from Paraguay, there will be some explaining to do if the Minas specimen is * not * rufimarginatus.

“So. we can put aside concerns that frater and rufimarginatus may not be sister taxa; it seems to be established that they are. That said, as usual I'm going to have a hard time voting for any pair of names in the form of "Xxxx Rufous-winged Antwren"; we just don't need yet more long compound bird names. I'm not thrilled with Piping Antwren and Churring Antwren, not because I object to basing the English name on the songs, but because I'm not sure that these two adjectives best describe the quality of each song (especially in the case of 'Piping'). I don't have better descriptive terms in mind, however, and could accept Piping and Churring if no one comes up with anything better.”

Comments from Bonaccorso: “A. YES. The differences in song and morphology seem to point to two different species. However, I am not entirely comfortable with the lack of genetic data and diagnostic plumage characters.”

Comments from Stiles: “A (the split of frater from rufimarginatus passed, but B (the E-name) did not; I gather that a 6:3 NO margin exists but am not entirely sure just what would be rejected as some did (or did not) favor conserving Rufous-winged as the name for both species, with the modifiers referring to the vocalizations of the loudsongs. I would prefer against using vocalizations, as all did not agree on the best adjectives for these – they are subjective in any case and could cause problems should frater be split in the future. Proposal 904 is a rerun of this one (see below).”