Proposal (405) to South American Classification Committee


Proposal 405A: Split Dysithamnus plumbeus and D. leucostictus (II)

Proposal 405B: Split Dysithamnus tucuyensis from D. plumbeus or D. leucostictus (II)

Proposal 405C: Adopt "White-streaked Antvireo" as English name for D. leucostictus (II)


These proposals were originally rejected as Proposals 261A-B on the basis that a soon-to-be-published paper was to address certain issues of relevance.  I refer to the original proposal set, which describes morphological and vocal differences between the taxa subject of this proposal. 

Subsequent to Proposals 261A-B, the split of D. plumbeus and D. leucostictus was further supported by a published study of sound recordings and statistical analysis of vocal variables, which concluded that the vocal differences between D. plumbeus and D. leucostictus are similar to or exceed vocal differences between some sympatric antbird species (Isler et al. 2008).  However, the split standard of three diagnosably different vocal variables in songs was (narrowly) missed as between D. leucostictus and D. tucuyensis.

Proposal 405A is effectively mandated for acceptance unless anyone wishes to doubt the methodology, results or approach of Isler et al. (2008), which one or two committee members have done on occasion on other proposals.  A "YES" vote is recommended on Proposal 405A (as it was on Proposal 261A).

Proposal 405B is a borderline proposal (as was stated to be the case for Proposal 261B).  Isler et al. (2008) "found it difficult to come to a recommendation as to whether tucuyensis and leucostictus should be considered distinct species" and concluded "although the data suggested that the vocalizations of tucuyensis and leucostictus may have diverged to a point comparable to that of sympatric species-pairs of thamnophilid antbirds, the results of the analysis were not conclusive."  In Proposal 261B, I stated my view on the split as: "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", which is a pretty similar conclusion.

Differences in song did not overlap for various characters studied by Isler et al. (2008) but were not fully diagnosable according to the statistical tests employed.  Calls were also different but Isler et al. (2008) concluded that the sample size and certain anomalous calls within the sample raised questions over splitting tucuyensis.  In Proposal 329 for Scytalopus diamantinensis, published diagnostic differences in call (together with certain differences in voice which whilst statistically significant appeared not to satisfy widely used tests of diagnosability) were considered sufficient to recognise a population at species rank and examples of sympatric antbirds with distinct calls but not songs are also known.  It is arguable that the differences in this instance are similar - and that the c. 750 km range disjunction between tucuyensis and leucosticta is significant.  One could consider reasons for going either way on this possible split depending on species concepts deployed and the extent of one's deference to historical treatments.  D. tucuyensis is certainly a distinctive phylogenetic species and on its own evolutionary course distinct from that of D. leucosticta.  Although Isler et al. (2008) were reluctant to recommend a change to status quo treatments, Part B of the proposal at least bears thought.

As for English names, Proposal 405C is recommended for acceptance in order to bring the SACC in line to prevailing English name usage by other authorities that accept this split and also due to "White-spotted Antvireo" being a misnomer, for the reasons set out in Proposal 261.

Asides: Being both a frequent user of the SACC list and author of proposals (which are usually rejected …), I have a couple of observations on this proposal and the previous proposal that may provide food for thought.

First, the original proposal on these taxa bears reflection in the context of Mark Robbins' proposal on "unpublished" vocalisation data (399).  It is of note that field guide taxonomic treatments and a non-peer reviewed SACC proposal, all based on subjective analyses, came to a similar conclusion as Isler et al. (2008)'s statistical analysis.

Secondly, it is worth considering whether the "status quo prevails" approach of SACC is justifiable in all instances, particularly where the SACC list is anomalous among modern peer publications in supporting a Peters lump and especially where threatened species are involved.  Rejection of Proposal 261A on the basis that it represented some form of "change" to the status quo was a surprising outcome.  The SACC's affirmation of what (even pre-Isler et al. 2008), was a little-recognised lump could have had negative conservation implications for D. plumbeus, a threatened species.  For example, BirdLife/IUCN considered adopting the lump as a result of the SACC's decision (but thankfully, decided against such an approach).  What of other threatened species that are split by many authors with subjective morphological and vocal support but that are lumped by SACC and which SACC (if past behaviour is an indication of future performance) would doubtless reject (e.g. Ortalis columbiana)?  I wonder if the quorum rules should better be reversed in such instances, or perhaps if committee members should consider more carefully whether their "NO" vote really maintains a status quo?  Frequent "NO" voting may give a favourable impression to other taxonomists that a committee member is a hardcore stickler for detail and scientific rigour.  However, this may not be a constructive approach in certain instances in light of the biodiversity crisis and the importance of taxonomic decisions to conservation decision-making.  This comment is limited to instances such as D. plumbeus/leucostictus in which the proposition that the SACC list represents a "status quo" has no or little support and affirmation of the SACC treatment would lump a threatened species into a widespread species of lower threat category.  Isler et al. (2008) said that distinctive subspecies should have protection as well, which is true, but unfortunately we all live in the real world where only species are considered relevant by governments and NGOs.  Obviously, conservation should not generally be a consideration relevant to taxonomy but perhaps it ought to be relevant to the processes by which votes of a taxonomic committee are conducted.

These are intended to be constructive comments from an onlooker.  I am not seeking to criticise individuals nor intending to tell you how to run your committee.

Recommendation: To accept Proposals 405A and 405C ("YES").  To pause and consider 405B.  Rejection pending further data and analysis of additional sound recordings was the recommended approach for 405B in Isler et al. (2008).


All on SACC references site.


Thomas Donegan, August 2009



Comments from Stotz:

405A: “YES. I voted for the previous proposal to split these two taxa (261A) and now with the Isler’s paper out, there seems to be no reason not to make this split.  These are very different birds.  I have to say that I would be surprised personally if these taxa turn out to be sisters when genetic studies are done.”

405B: “NO.  The data supporting splitting tucuyensis from leucostictus just seems insufficient currently.

405C: “Yes This is the appropriated English name for leucostictus.”

Comments from Stiles: “YES to A and C, now that we have both morphological and vocal evidence favoring this split.  NO, at least for now, on B. Given that Isler et al. also recommended caution, and that these two are present in similar life zones on adjacent mountain ranges, I feel that a conservative approach is best on this one.”

Comments from Nores:

“A: YES.  Repito lo que puse en la propuesta #261 “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 popr 4000 km de rain forest. Ahora agrego: con lo expresado en el paper de Isler et al. (2008) no veo razones para no separar las especies. Estas difieren, además del color, en seis características vocales:  “number of notes, duration, change of pace, change of note length, peak frequency, and change of peak frequency.”

“B.  NO. Aunque el caso es algo parecido al anterior, las diferencias morfológicas y la aislación de los rangos son mucho menos marcados. Además, Isler et al. (2008) mencionan que no encontraron diferencias estadísticamente significativas en la vocalizaciones entre tucuyensis and leucostictus y recomiendan tener caución.”

Comments from Zimmer:


“Proposal #405B: Split Dysithamnus plumbeus and D. leucostictus.  I vote YES.  I don’t think there was ever any doubt about this one, at least not among those who have field experience with both plumbeus and leucostictus.  As Doug stated, it would almost be surprising if these two even turn out to be sister species when the molecular dust settles.  However, I feel that I must respond to some of the issues raised in this proposal.  I don’t agree that the earlier committee rejection of Proposal 261 was based on a “status quo prevails” philosophy.  Rather, because we knew that a formal analysis was already in preparation (Isler et al), it made sense to wait for actual data, particularly since part of Proposal 261 also dealt with the potential splitting of tucuyensis from leucostictus, which was far from straightforward.  The recognition of plumbeus as specifically distinct could certainly have positive conservation implications for this threatened bird, and I think all of us are aware that endangered species receive more conservation attention than endangered subspecies.  For that reason, I agree that it is particularly important that our taxonomy reflects the true species-level biodiversity that is present in South America, so that distinctive taxa are not allowed to slip into extinction for want of attention.  However, I don’t think conservation considerations should drive taxonomic decisions.  To be stampeded into recognizing every threatened or potentially threatened population as a distinct species, regardless of the existence of supporting evidence, would merely place us in the same realm of politically compromised scientists as the ones used by the last US administration to try to cook the science (in the opposite direction) on everything from California Gnatcatchers to Snowy Plovers and Spotted Owls.  If our taxonomic decisions are not based on the best science available, then the credibility of all of our decisions are tainted, and it only exposes threatened species to attack the next time the political pendulum swings back to favoring the folks that want to de-list everything to facilitate development.  We are not doing these endangered populations any long-term favors by getting ahead of the evidence on elevating them to species-status, only to have shoddy science used as the justification for governmental agencies not taking our taxonomic recommendations seriously.


“All of this having been said, the evidence for separate-species status for D. plumbeus versus the leucostictus/tucuyensis group is (happily) unambiguous and based on solid, published analysis.



“Proposal #405B:  Split D. tucuyensis from D. plumbeus or D. leucostictus.  This one is not so clear-cut.  My gut feeling is that the two taxa are probably good species, and that, if nothing else, given their respective distributions, they are on separate evolutionary trajectories.  However, the only published analysis has failed to make a clear case for splitting.  In the interest of keeping our taxonomic decisions evidence-based, I vote NO for now.  I’m guessing that as additional archived vocal samples become available, distinctions between leucostictus and tucuyensis (particularly in calls) will pass statistical rigor.


“Proposal #405C:  Adopt “White-streaked Antvireo” as English name for D. leucostictus.  I vote YES.”


Comments from Pacheco:

“Proposal (#405A): Split Dysithamnus plumbeus and D. leucostictus (II): YES. Os dados disponíveis corroboram com evidente clareza a proposta.


Proposal (#405B): Split Dysithamnus tucuyensis from D. plumbeus or D. leucostictus (II): NO. Enquanto os dados necessários para avaliação da proposta não estiverem disponíveis.”