Proposal (786) to South American Classification Committee
Split Slaty Thrush Turdus nigriceps into two species
Background: Turdus nigriceps (Slaty Thrush), as recognized by SACC, is a polytypic species with two disjunct populations. Nominate nigriceps occurs in the Andes, with a curious distribution: it breeds in southern Bolivia and northwestern Argentina, with another very disjunct breeding population in southwestern Ecuador and northwestern Peru; and it is a nonbreeding migrant to the east slope of the Andes from southern Ecuador south to northwestern Bolivia. The other subspecies, subalaris, breeds in southern Brazil, northeastern Argentina, and eastern Paraguay, and is a nonbreeding migrant north to south central Brazil.
The two taxa have a generally similar plumage pattern, but subalaris overall is paler and browner than nigriceps. Compared to male nigriceps, male subalaris has upperparts that are more washed with olivaceous; the crown is concolor with back (crown black in nigriceps); has a prominent white crescent on the upper breast, below the throat (crescent lacking in nigriceps); the center of the belly is more extensively white; and the underwing coverts are white (gray in nigriceps) (Hellmayr 1934, Ridgely and Tudor 1989). Less attention is paid, at least in the recent literature, to differences in the female plumage, but female subalaris apparently also has white crescent on the upper breast, again less apparent in female nigriceps. See, for example
At least as late as Hellmayr (1934), nigriceps and subalaris were recognized as separate species. They were lumped, without comment, by Ripley (1964), and this was followed by Meyer de Schauensee (1966). They were split again by Ridgely and Tudor (1989):
Obviously well isolated geographically, they also differ in plumage and have rather different songs, that of Andean [nigriceps] being more jumbled and musical (not so squeaky).
The songs of the two are further described as a series of rather high, jumbled phrases, some of the notes quite high-pitched in nigriceps, compared to a short series of high pitched notes with an oddly squeaky, bell like quality in subalaris (Ridgely and Tudor 1989, 2009). I am not aware of any further analysis of these songs. Representative examples of songs of both can be heard at Macaulay Library and at xeno-canto (separate pages for nigriceps and for subalaris); examples are
This split has been widely adopted (e.g., Clement 2000, del Hoyo and Collar 2016), but acceptance of the split has not been universal (e.g., Dickinson and Christidis 2014).
New information: There are several recent molecular phylogenies of the genus Turdus that touch on Turdus nigriceps. Voelker et al. (2007) used only mitochondrial DNA, but had a very wide sampling of species of Turdus, although unfortunately they included only nominate nigriceps (a sample from Argentina). They resolved nigriceps as a member of a clade that also included Turdus fulviventris (Chestnut-bellied Thrush), Turdus olivater (Black-hooded Thrush), Turdus fuscater (Great Thrush), Turdus serranus (Glossy-black Thrush), and Turdus chiguanco (Chiguanco Thrush).
Nylander et al. (2008) also had wide sampling of species of Turdus, and used both mitochondrial and nuclear DNA. As with Voelker et al., they included only nominate nigriceps (a sample from Ecuador), and they too place nigriceps in a clade with fulviventris, olivater, fuscater, serranus, and chiguanco (although their topology within this clade is different from that of Voelker et al.).
Cerqueira et al. (2016) used both mtDNA and nuDNA to investigate relationships within the Turdus ignobilis (Black-billed Thrush) complex. They sampled extensively within three of the five subspecies of ignobilis. For data on outgroups, they primarily relied on mtDNA data from Voelker et al. and from O’Neill et al. (2011), but Cerqueira et al. also produced fresh data, for both mtDNA and nuDNA, for nominate nigriceps (two samples from Bolivia) and for two samples of subalaris (two samples from Brazil). In a by now familiar pattern, Cerqueira et al. found that nigriceps belongs to the same clade as fulviventris, olivater, fuscater, serranus, and chiguanco. In contrast, subalaris belongs to a very different clade, clustering in a clade with members of the ignobilis group, and with T. maranonicus (Maranon Thrush), T. lawrencii (Lawrence’s Thrush), T. eremita (Tristan Thrush), and T. amaurochalinus (Creamy-bellied Thrush).
Avendaño et al. (2017) took another look at the ignobilis complex, within which they sampled all taxa assigned to ignobilis. The trees that they published did not include as many species of Turdus as the other studies, but they included both nigriceps and subalaris (for both of which they used data from Cerqueira et al.). Avendaño et al. again recovered subalaris as part of a clade with the ignobilis group, maranonicus, lawrencii, eremita, and amaurochalinus. Nominate nigriceps is well outside this clade (but its affinities are not resolved here, as the trees published by Avendaño et al. include only a few species of Turdus outside of the clade that includes ignobilis).
Analysis: Differences in both plumage and song are highly suggestive that nigriceps and subalaris are different species, as was intuited long ago by Ridgely and Tudor (1989). Those authors assumed, however, that nigriceps and subalaris still were sister taxa, whereas the phylogenetic evidence shows that a polytypic Turdus nigriceps is paraphyletic: not only is it clear that nigriceps and subalaris are separate species, but these two are not at all closely related to each other.
English names: For almost 30 years, these two species have been known as Andean Slaty Thrush (nigriceps) and Eastern Slaty Thrush (subalaris) (Ridgely and Tudor 1989, Sibley and Monroe 1990, Clements 1991, Monroe and Sibley 1993, Clement 2000, Clements 2000, Mazar Barnett and Pearman 2001, Ridgely and Greenfield 2001, Guyra Paraguay 2004, Gill and Wright 2006, Restall et al. 2006, Clements 2007, Ridgely and Tudor 2009, del Hoyo and Collar 2016). These names of course stem from a time when nigriceps and subalaris were assumed to be sister taxa; knowing that this is not the case, and if we were starting from scratch, completely different names for each might be warranted. There is no history of separate names for them, however. Meyer de Schauensee (1966) (or, I assume, Eugene Eisenmann in Meyer de Schauensee) proposed the names Black-capped Thrush for nigriceps, and Slaty-capped Thrush for subalaris, but those are not terrific names, and I am not aware that these ever were adopted by anyone. It is best, then, to retain the names that are in (very) wide use. Note that Slaty Thrush is not hyphenated in this case, as it is not a group name.
Recommendations: I suggest breaking this proposal down into two parts:
Part A): to split Slaty Thrush Turdus nigriceps into two species. My recommendation is Yes.
Part B): to adopt Andean Slaty Thrush as the English name for Turdus nigriceps, and Eastern Slaty Thrush as the English name for Turdus subalaris. My recommendation is Yes.
Avendaño, J.E., E. Arbelaez-Cortés, and C.D. Cadena. 2017. On the importance of geographic and taxonomic sampling in phylogeography: a reevaluation of diversification and species limits in a Neotropical thrush (Aves, Turdidae). Molecular Phylogenetics and Evolution 111: 87–97. https://doi.org/10.1016/j.ympev.2017.03.020
Cerqueira, P.V., M.P.D. Santos, and A. Aleixo. 2016. Phylogeography, inter-specific limits and diversification of Turdus ignobilis (Aves: Turdidae). Molecular Phylogenetics and Evolution 97: 177–186. https://doi.org/10.1016/j.ympev.2016.01.005
Clement. P. 2000. Thrushes. Princeton University Press, Princeton, New Jersey.
Clements, J.F. 1991. Birds of the word: a checklist. Fourth edition. Ibis Publishing Company, Vista, California.
Clements, J.F. 2000. Birds of the word: a checklist. Fifth edition. Ibis Publishing Company, Vista, California.
Clements, J.F. 2007. The Clements Checklist of the birds of the world. Sixth edition. Cornell University Press, Ithaca, New York.
Dickinson, E.C., and L. Christidis. 2014. The Howard & Moore complete checklist of the birds of the world. Fourth edition. Volume 2. Aves Press, Eastbourne, United Kingdom.
Gill, F., and M. Wright. 2006. Birds of the world: recommended English names. Princeton University Press, Princeton, New Jersey.
Guyra Paraguay. 2004. Lista comentada de las aves de Paraguay/Annotated checklist of the birds of Paraguay. Asociación Guyra Paraguay, Asunción.
Mazar Barnett, J., and M. Pearman. 2001. Lista comentada de las aves Argentinas/Annotated checklist of the birds of Argentina. Lynx Edicions, Barcelona.
Meyer de Schauensee, R. 1966. The species of birds of South America and their distribution. Livingston Publishing Company, Narberth, Pennsylvania.
Monroe, B.L., Jr., and C.G. Sibley. 1993. A world checklist of birds. Yale University Press, New Haven, Connecticut.
Nylander, J.A.A., U. Olsson, P. Alström, and I. Sanmartin. 2008. Accounting for phylogenetic uncertainty in biogeography: a Bayesian approach to dispersal-vicariance analysis of the thrushes (Aves: Turdus). Systematic Biology 57: 257-268. https://doi.org/10.1080/10635150802044003
O’Neill, J.P., D.F. Lane, and L.N. Naka. 2011. A cryptic new species of thrush (Turdidae: Turdus) from western Amazonia. Condor 113: 869-880. https://doi.org/10.1525/cond.2011.100244
Restall, R., C. Rodner, and M. Lentino. 2006. Birds of northern South America: an identification guide. Yale University Press, New Haven, Connecticut.
Ridgely, R. S., and P. J. Greenfield. 2001. The birds of Ecuador. Cornell University Press, Ithaca, New York.
Ridgely, R. S., and G. Tudor. 1989. The birds of South America. Volume I. University of Texas Press, Austin, Texas.
Ridgely, R. S., and G. Tudor. 2009. Field guide to the songbirds of South America. The passerines. University of Texas Press, Austin, Texas.
Ripley, S.D. 1964. Subfamily Turdinae, thrushes. Pages 13-227 in E. Mayr and R.A. Paynter, Jr. (editors), Check-list of birds of the world. Volume X. Museum of Comparative Zoology, Cambridge, Massachusetts.
Sibley, C.G., and B.L. Monroe, Jr. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, Connecticut.
Voelker, G., S. Rohwer, R.C.K. Bowie, and D.C. Outlaw. 2007. Molecular systematics of a speciose, cosmopolitan songbird genus: defining the limits of, and relationships among, the Turdus thrushes. Molecular Phylogenetics and Evolution 42: 422-434. https://doi.org/10.1016/j.ympev.2006.07.016
Tom Schulenberg, April 2018
Comments from Robbins: “A. YES, genetic data clearly establish that nominate nigriceps and subalaris are not closely related and subalaris merits recognition as a species.”
Comments from Remsen: “A. YES. Genetic data require recognition of subalaris as a species. Amazing result given phenotypic similarity.
“B. NO. This isn’t a split involving sister taxa; if that were the case, I would vote yes for the proposed names. But the key finding is that these two aren’t particularly closely related. Thus retaining “Slaty Thrush” in their names perpetuates that misconception, even unhyphenated. Yes, they are both slaty in terms of color, but so are other thrushes. Why maintain the connection in the English name? The adoption of Eastern Slaty Thrush by HBW etc. was done under the assumption that the two species were sisters, and so we can only speculate on whether that name would have been adopted had the true relationships been known. The “Eastern” part makes sense only as counterpart to Andean Slaty Thrush. Thus, I don’t think we should worry about stability given that the existing name is based on misinformation. Leaving nigriceps as Slaty Thrush has the advantages of (1) that name staying with the species for which it was intended and (2) avoiding a compound name that in this case does not reflect relationships. That’s the easy part. The hard part is concocting a novel name for subalaris.” Hellmayr (1934), who treated it as a separate species, called it “Behn’s Thrush”, for W. F. G. Behn, who according to Beolens et al. (2014; The Eponym Dictionary of Birds) was “a German explorer who is famed for his crossing of South America. He was the Director of the Zoological Museum of Christian Albrechts University of Kiel (1836-1868). This is the same Behn of Myrmotherula behni, Trogon curucui behni, and Brotogeris chiriri behni. Most people don’t like eponymous English bird names, so this would not likely be a popular choice. “Subalaris” means “under the arms”, so no help there. However, if we put our heads together, I predict we’ll be able to do better than “Eastern Slaty Thrush”, which in my opinion is not only insipid but misleading.”
Comments from Stiles: “A: YES to splitting subalaris from nigriceps, a move clearly mandated by the phylogeny; B. YES to retaining Black-capped for nigriceps; C: NO, for reasons given by Van. A couple of suggestions (I haven’t checked the voluminous English nomenclature of Turdus for synonyms: Plain-capped (to contrast with Black-capped); or Olive-gray, to emphasize the color difference of the dorsum.”
Comments from Jaramillo: “A: YES – straight forward. B YES – they are in usage already, so in terms of name stability and the fact there are no good alternative names that are in use, I think one has to go with this choice.”
Comments from Stotz: “A: YES. B. NO. I don’t have a vote here at this point. I agree that the fact that the two Slaty Thrushes are not closely related undermines Andean and Eastern Slaty Thrush as a reasonable alternative. I also have a problem with leaving nigriceps as Slaty Thrush. 1st it doesn’t follow our “rule” regarding English names, which ideally we would follow. But the real problem is that I think most people think of “Slaty Thrush” as being the widespread eastern migratory form. I think applying it to the much more poorly known Andean form is a mistake. One final comment on this is it seems like a number of committee members prefer keeping the old English name with the nominate form when I split occurs. I can be talked into that, but in general, I think it is a mistake, because you end up with a daughter taxon with both the same English and scientific name as the broader species concept. This makes confusion over what species concept you are using more of an issue than when the old English name and <in prep>
Comments from Pacheco: “YES. Highlighting one of the affirmatives of Tom's proposal (…) “it clear that nigriceps and subalaris are separate species, but these two are not at all closely related to each other.”
Comments from Areta: “YES. Phylogenetic data clearly supports the recognition of two species, as vocalizations and plumage have long suggested. It is interesting that these two are not even sister species.”
Comments from Zimmer: “A. YES. This one was overdue, based on plumage differences, vocal differences, ecological differences, and the fact that the lump was a typical Peters-style fiat without comment. All of this now supported by genetic data. B. NO, for the reasons cited by others. “Slaty Thrush” no longer works as a group name, given that the two species are not sisters.”
Proposal (786B.1) to South American Classification Committee
Establish English names for Turdus nigriceps and Turdus subalaris
Proposal 786B above (Eastern Slaty Thrush and Western Slaty Thrush) did not pass, and because I was one of the NO voters, I’ll take responsibility for another iteration. See comments above for background.
The objection to Eastern Slaty Thrush and Andean Slaty Thrush, despite their long history documented by Tom, is that even without hyphens, these names perpetuate the incorrect notion that the two species are related. These names would in a sense negate finding of Cerqueira et al. (2016) and Avendaño et al. (2017) that these two are not even in the same section of the genus --- see the tree in the main proposal. Turdus nigriceps is sister to a group of largely Andean thrushes that are slaty blackish to black (T. fuscater, T. serranus, T. chiguanco), whereas subalaris is sister to a group of lowland thrushes that are more brownish (T. ignobilis etc.). (Check online photos and the specimen photos below of Turdus nigriceps to see how much darker it is than T. subalaris; thus, fits fairly nicely in the blacker Andean group.)
Reversing my initial comments (above), retaining Slaty Thrush for one of the daughters IS unacceptable in this case in my opinion – it’s a good example of why the guideline of creating new names for daughters is the best practice because who would remember which is which? Doug thinks of subalaris when he sees Slaty Thrush, but I’m the opposite – for me, and probably others working with Andean birds, “Slaty Thrush” has always been nigriceps. Furthermore, “Slaty” is not a very good name for subalaris: see the photos – it’s really not much grayer than a lot of Turdus, in contrast to the obviously slaty nigriceps. In fact, I now wonder why they were considered conspecific in the first place; Hellmayr certainly had it right, but Ripley (Peters) botched this badly.
As you all know, I’m a major proponent of stability in English names because “improving” them defeats their purpose. The exception, in my view, is when they are misleading. At face value, Andean Slaty and Eastern Slaty aren’t descriptively misleading; however, they were clearly intended to connote a sister relationship, even before the Cerqueira et al. (2016) and Avendaño et al. (2017) data falsified this. Thus, to perpetuate those names is actively misleading. Stability in this case, in my opinion, needs to be disrupted. In this case, stability = liability in my opinion.
So, I recommend going with the Meyer de Schauensee names mentioned by Tom, even though they were never used by anyone else: Black-capped Thrush for nigriceps, and Slaty-capped Thrush for subalaris. They are not diagnostic, but at least not inaccurate. Black-capped is a translation of the scientific name, aiding remembering which one is which, and Slaty-capped maintains a slim connection to Slaty. A potential objection to both of them being “Something-capped” might still imply a relationship, being the only South American “-capped” thrushes, so if someone has a better idea for subalaris, I’m receptive. I assume Hellmayr’s “Behn’s Thrush” (see comments above) is not a popular choice.
Van Remsen, June 2018
Comments from Stotz: “YES. I think this is the best option we have. At least they are not completely new names, and don’t give the misimpression of a close relationship between the two species.”
Comments from Josh Beck: “Narosky & Yzurieta's "Birds of Argentina and Uruguay" guide is the only reference I know that doesn't use Andean and Eastern Slaty Thrush but rather uses Black-capped Thrush for nigriceps and Slaty Thrush for subalaris. I don't have any strong opinions on the names proposed, but if there is a strong dislike for Slaty-capped Thrush an alternative that occurs might be Mata Thrush or Atlantic Thrush or another more clever biogeographic reference, as this is the only Turdus that is essentially endemic to the Atlantic Rainforest.”
Comments from Jaramillo: “YES -- go with the “-capped” names, I don’t think they suggest relationship in this case.”
Comments from Schulenberg: “NO. Neither name is inaccurate, but at the same time neither gets to the heart of what each species looks like. And both names are pretty blah; one blah name I could handle, two similar blah names is not appealing. And I might have trouble remembering which blah name refers to which species. Dan Lane says that in his experience, nigriceps typically is in alder thickets, and so he suggested to me that Alder Thrush would be an appropriate name for that species. I could live with Alder Thrush (nigriceps) and Slaty-capped Thrush, if anyone else would go along. I'm not worried about coining novel names in this case; as far as I am aware, no one ever has used the names (coined by Eisenmann?) in Meyer de Schauensee, so these effectively are new names anyway. Even better, of course would be a novel name for subalaris that, like Alder, reflects its biology.”
Comments from Stiles: “Black-capped is fine with me, and I'll go with Slaty-capped if that gets a majority, but I really don't like this name much - mainly because the bird is not really "capped" at all - its upperparts appear uniform slaty gray. Is there a Slaty-backed Thrush anywhere else?”
Comments from Zimmer: “NO to “Black-capped” and “Slaty-capped” as English names for nigriceps and subalaris. I don't either of these names is particularly descriptive (neither nigriceps nor subalaris looks particularly "capped"), and by going with something-capped for both species, I think that implies sister-status in the same way that "something Slaty Thrush" (with or without the hyphen) does.
“I could go with “Alder Thrush” for nigriceps, or something like “Cinereous Thrush” or “Saturnine Thrush”, since it is distinctly darker and grayer than subalaris. For subalaris, I would propose a novel name based on what I think is its most distinctive character — its voice. This bird has a unique, jangling quality to the song that is not matched by any bird that I can think of (and very different from the vocal quality of nigriceps). A quick look at an online dictionary shows the verb form of “jangle” defined as: make or cause to make a ringing metallic sound, typically a discordant one “a bell jangled loudly”. The noun form is described as a “ringing metallic sound”. These definitions fit the jangling, discordant, bell-like songs of subalaris perfectly. So, I would propose calling it “Jangle Thrush”, "Jangling Thrush", or, the slightly less descriptive “Chiming Thrush”, as a name that is both novel, memorable, and descriptive.”
Comments from Mark Pearman: “I agree that these species do not look at all capped in the field and would avoid those names, It's the whole of the head that contrasts in nigriceps yet this can be difficult to see when you are often looking up at them high in the canopy.
“Yes, nigriceps occurs in alder woodlands, but it is far more common and even abundant in the mixed yungas forest below that i.e. c. 600 to 1500 m. So, while not being exclusive to alder woodland, in some areas, Glossy-black Thrush T. serranus is more common than nigriceps in that habitat, and again I would avoid the name Alder Thrush.
“It is true that these thrushes have very distinctive songs. To my ear nigriceps delivers a jangling series, whereas subalaris sounds more like chiming. This is subjective and different people are likely to have a different interpretation.
“Finally, and although the species are not closely related, I have no problem at all with the names Andean Slaty Thrush and Eastern Slaty Thrush. Firstly they have been around for many years and are in common usage. Secondly, they are informative and tell you where the birds are found and that (the males) are slaty.”
“I recommend sticking with Andean Slaty Thrush T. nigriceps and Eastern Slaty Thrush T. subalaris.”
Comments from Dan Lane: “For subalaris, some possibilities could be Mata Atlantica Thrush, Clanging Thrush, Chiming Thrush.”
Additional comments from Stiles: “The Slaty Thrush split was accepted 11-0, no problem. However, the E-names are sufficiently bogged down that no clear consensus seems to be emerging. So, a couple of fresh suggestions that hopefully won't simply muddy the waters further. Going through the extensive index or E-names for "thrush" in HBW vol. 10, I found (to my surprise) that there is no "Black-headed" Thrush! So, given the objections to the "capped" names and a fairly general dislike for E. and W. Slaty Thrushes, I would suggest Black-headed Thrush for nigriceps - it is a more direct translation of the Latin name, and also more accurately descriptive. For subalaris, several people have suggested something recalling its voice, but the suggestions have been a bit contradictory: "jangling" has been proposed for subalaris, but Mark P. applies it to nigriceps! R&T's description of the song of subalaris is "squeaky, bell-like" but I have a hard time uniting "squeaky" with "jangling", and "chiming" to me implies a more ringing, pure tone. However, another name given in HBW for subalaris is "Blacksmith" Thrush. I suspect that this may derive from a common name given by Pinto as used in Brazil: "ferreiro". Also somewhat in line here: a synonym of subalaris given by Hellmayr was "metallophonus". All this brought out of deep recall an experience of mine around 1971 in a tiny hamlet in Costa Rica, when I spent a night in a room near to a blacksmith's forge.. he was working late, and I remember dozing off to the accompaniment of his hammer going "clink..clink..clink". So, how about "Clinking Thrush"?? (Try this on with those familiar with this species..)”
Final comments from Remsen: “This proposal is officially stale-mated. Even expanding the vote to include Mark Pearman and Steve Hilty will not help because it is clear that Mark, from his comments above, would vote NO. So, I am asking one or more of the NO voters (Tom, Doug, Kevin; or Mark P.) to try a new proposal. Note that because this split does not involve true phylogenetic parent-daughter split, one of the pseudo-daughters, presumably nigriceps, could retain “Slaty Thrush”.
Comments from Stiles: “Regarding E-names, I suggested Black-headed Thrush for nigriceps (but could live with Slaty Thrush if this looks like achieving a majority –after all, it is the “slatier” of the two). If the people who prefer a voice-related name for subalaris can get together on this, I’ll go along. Not much to recommend regarding conspicuous field marks in its almost spectacularly blah plumage.. However, looking through my Smithe color swatches, the closest I come is –Drab! So I’ll toss Drab Thrush or Drab-gray Thrush into the hat for selection of an E-name!”