Proposal (572) to South American Classification Committee


Merge Upucerthia validirostris and U. jelskii into a single species


Background: The Buff-breasted Earthcreeper (Upucerthia validirostris) is endemic to western Argentina, and the Plain-breasted Earthcreeper (U. jelskii, including subspecies saturata in the north and pallida in the south), ranges from northern Peru to northwestern Argentina. They have been considered subspecies, as components of a superspecies, and as different species.


Current SACC note reads:


 Although Upucerthia jelskii is considered separate species from U. validirostris in most recent classifications (e.g., Meyer de Schauensee 1970, Ridgely & Tudor 1994), evidence for their treatment as such is weak (Remsen 2003), and perhaps a return to earlier classifications that treated them as conspecific (e.g., Cory & Hellmayr 1925, Peters 1951) is warranted. They form a superspecies (Sibley & Monroe 1990). A report of sympatry in southern Bolivia (Cabot 1990) is based on a misidentification (Remsen 2003). Genetic data (Chesser et al. 2007, Fjeldså et al. 2007) confirm that they are sister taxa but weakly differentiated (Derryberry et al. 2011).  Areta & Pearman (2009, 2013) found no differences in their voices.  Areta & Pearman (2013) proposed that they be treated as conspecific.  SACC proposal badly needed.”


New information: Areta & Pearman (2013) argued for the merging of U. validirostris and U. jelskii as follows in the abstract. “From north to south, a morphocline, involving an increase of rustiness of the plumage and of ~15% in bill length, 10% in wing length, and 20% in tail length, links jelskii to validirostris. The cline linking jelskii and pallida is gradual, over ~1800 km; that between pallida and validirostris is steep, over ~80 km. The northernmost record of validirostris is from the northern Calchaquies Valley, Salta, northwestern Argentina, a valley surrounded by mountains of up to ~6300 m above sea level through which the lowest pass is at over 4900 m, forming a barrier between validirostris and the southernmost record of pallida to the north. The song, continuous song, duet, and call of validirostris are structurally indistinguishable from those of jelskii/pallida and from the single available recorded song of saturata. In all playback experiments, validirostris answered by approaching and vocalizing to voices of validirostris and jelskii/pallida and vice versa. Treatment of validirostris as a single species is warranted, and three subspecies can be tentatively recognized: southern validirostris (large, rufescent birds with buff bellies restricted to Argentina), central and northern jelskii (small, pale birds ranging from northwestern Argentina to central Peru), and northern saturata (small, dark, and brownish birds in northern central Peru).”


Further detail on the importance of playback experiments for our recommended taxonomic treatment is pasted from our paper (Areta & Pearman 2013: 138; emphasis added): “In the valleys of Putre, northern Chile, and their environs, U. albigula coexists with U. validirostris pallida without any sign of intergradation (Johnson et al. 1967, Areta and Pearman 2009) and exemplifies species-level differentiation in partly syntopic species. At higher elevations and in drier, flat, or broken areas in the same mountains, only U. validirostris pallida is found, whereas only U. albigula is known to frequent Polylepis groves. The voices of these two species differ markedly, and in six reciprocal playback experiments that we conducted in October 2011 in Putre, each ignored the vocalizations of the other species and responded strongly to its own, suggesting that there is neither interspecific territoriality nor species-level recognition between them. Two parapatric species, U. saturatior in the Patagonian forests and U. dumetaria in open steppe habitats, likewise ignore each other’s vocalizations. In our previous work (Areta and Pearman 2009), we were unable to test the response of saturatior to vocalizations of dumetaria while showing that dumetaria ignores the vocalizations of saturatior. We are now able to confirm that saturatior ignores the vocalizations of dumetaria while strongly responding to its own on the basis of three “sandwich” playback experiments at Paso del Arco, Neuquén, Argentina, in December 2011.


Allopatry has traditionally been considered an impediment to the solid evaluation of the species status of such geographically separate populations (Mayr 1963, Remsen 2005). The spatial array of species-level taxa in Upucerthia coupled with their divergence in vocalizations and resulting behavioral data allow us to shed new light on this reasoning. Despite extensive geographic variation in plumage and size, both U. dumetaria and U. validirostris respond to playback of very distant populations within their wide distributions. The strong response of Upucerthia earthcreepers to vocalizations of distant populations with similar song and their lack of response to vocalizations of nearby, parapatric, or even syntopic populations with dissimilar songs argue strongly that the taxonomic status of allopatric populations can be adequately evaluated with playback experiments. Moreover, in the case of populations separated on isolated mountains, the same situation of allopatry would impede their assignment to the same species under the traditional view, but our studies suggest that this problem can be easily avoided with the aid of playback experiments. In this sense, playback experiments in Upucerthia earthcreepers constitute adequate simulations of syntopy of allopatric populations and of populations isolated by distance.”


Recommendation: We recommend a YES vote to this proposal, which would merge Upucerthia jelksii into U. validirostris, which has nomenclatorial priority.



 Areta, J.I. & M. Pearman. 2013. Species limits and clinal variation in a widespread high Andean Furnariid: the Buff-breasted Earthcreeper (Upucerthia validirostris). Condor 115:131-143.


Nacho Areta & Mark Pearman, March 2013





Comments from Remsen: “YES. The evidence is overwhelming.  Outstanding work by Nacho and Mark.”


Comments from Stiles: “YES. A very good combination of broad-scale morphological data plus careful, well-controlled playback experiments – truly a model study in this respect.”


Comments from Pacheco:  “YES.  Reasons to consider the two taxa as part of a single biological species are well presented and well thought-out by Nacho and Mark.”


Comments from Frank Rheindt: Areta & Pearman (2013) propose the lumping of Upucerthia validirostris and U. jelskii under the BSC based on their conclusion that there is no vocal differentiation, and that there is a morphological cline between them. They do not discuss recent molecular work (Derryberry et al. 2011) in great detail.


“I find Areta & Pearman’s (2013) work to be one of the strongest biometric papers published about furnariids in recent years because it is based on an impressive sample size and range. Even so, I disagree with their conclusions. I do not think Areta & Pearman’s (2013) work is sufficient to lump these two forms. In fact, I think their biometric analysis may be in partial disagreement with a lump.


“Here are the reasons for my assessment:


“Vocal analysis:

Areta & Pearman’s vocal analysis was not based on rigorous statistical comparisons. It was merely a superficial inspection of sonograms and personal acoustic sound impressions. I do not wish to belittle such qualitative inspections (in fact, I have been guilty of publishing similar non-statistical vocal inspections in previous work on Zimmerius). However, we know from a large number of studies (e.g. dozens of papers by the Islers, Whitney etc.) that closely-related but well-differentiated suboscines can have extremely similar vocalizations that differ only in a couple of parameters and can only be detected by measuring vocal traits across large datasets. I don’t think Areta & Pearman’s superficial inspection would have been able to pick up vocal differences such as those between various members of the Warbling-Antbird complex or the Herpsilochmus complex. Looking at their Fig. 4, it is entirely plausible that an analysis of more recordings would show significant differences between U. jelskii and U. validirostris in frequency range (which seems to be consistently smaller in U. validirostris) and other traits.



Areta & Pearman consider their playback experiments (n=44) one of the strongest indications of conspecificity. However, Tobias & Seddon’s (2009, Evolution) playback experiments between warbling antbirds show that response to conspecific and non-conspecific song can be equally strong in suboscines. Considering that U. jelskii and U. validirostris are probably much more closely related to each other (Derryberry et al. 2011) than the two warbling antbirds analyzed by Tobias & Seddon (2009), the strong reaction to non-conspecific playback should not come as a surprise.



Areta & Pearman’s biometric analyses show there is a steep cline over 80km between pallida (a subspecies of jelskii) and validirostris, while there is a shallow cline over 1800km between pallida and jelskii. While the interpretation of this pattern is a matter of dispute, I would think most proponents of the BSC (including Ernst Mayr himself) would have interpreted this result as an indication for two species, not one species. Consider that the 80km cline may in fact be much narrower if Areta & Pearman had additional samples from the intervening areas. This sort of steep cline between two well-differentiated forms sounds like a narrow hybrid zone to me.

People argue whether forms that meet at narrow hybrid zones are two biological species or one (and there is always subjectivity in what is ‘narrow’ and what is not). Ernst Mayr (the ‘father’ of the BSC) was very explicit in his acceptance of most such forms as two different species (see e.g. Mayr 1970, p. 56; Mayr 1999). For him, as for many other proponents of the BSC these days, narrow hybrid zones that persist over time indicate that there may be a resistance on part of the two forms to fuse into one reproductive entity (which would have led to the widening of the cline over time).


“We don’t know how new this steep cline between validirostris and pallida is, and whether it is expanding, stable or contracting. Only additional vocal and genetic work on the validirostris – pallida cline will show the nature of the reproductive interactions between these two forms. Until such time, the status quo should be maintained.”


Response from Areta and Pearman: “We were surprised by Rheindt’s comments on our recent paper on the taxonomy of Upucerthia validirostris which seem to have missed many important facts in our comparative studies and which stem from inadequate comparisons with phylogenetically distant taxa. We detail our thoughts below.


“Rheindt wrote that “playback experiments between warbling antbirds show that response to conspecific and non-conspecific song can be equally strong in suboscines”. The comparison is misleading on three counts. First, it compares the results obtained with Thamnophilids (and with emphasis on a very special situation of two species which differ in habitat use in a scenario of partial sympatry) to those of Furnariids. Second, it misses the fact that in Upucerthia (the proper group to compare with) we have shown that different species pairs with narrowly parapatric distributions, which differ in habitat preferences, and have completely different vocalizations ignore playback of each other. Third, it is unacceptable to jump to a conclusion at the ‘suboscine’ level based on a few examples. For a long time Suboscines were believed not to learn their vocalizations based on detailed studies in a few tyrant flycatchers by Don Kroodsma. Later on, Kroodsma showed that bellbirds learn their vocalizations demonstrating that the “non-learning Suboscine” concept was an unjustified overgeneralization. In this rather similar case, Rheindt wishes to extrapolate what happens in one peculiar example in one family of Suboscines to all Suboscines in order to reject our findings. We think this weak theoretical basis renders his arguments invalid.


“Likewise, his proposed need of ‘rigorous statistical comparisons’ based on a framework that was developed for the vocally very different Thamnophilids is misleading. In Furnariids such as Cinclodes, Upucerthia and Syndactyla, in which vocal variation between consecutive vocal bouts of the same individual is large, it is very difficult to make any meaningful comparison in statistical terms, as it is virtually impossible to find homologous points in their vocalizations for such comparisons. Our examination was neither ‘mere’ nor ‘superficial’ as stated by Rheindt. It was a comparison which took into consideration the fact that vocalizations are very hard to compare quantitatively in this group and thus it focused on the shape of notes. Once again, this method of comparison yielded consistent results: vocal variation between species was noticeable and obvious (and concordant with lack of playback responses) and variation within a species was minor and shape was consistent (and concordant with strong playback responses, so strong that there was no need for any statistical analysis to uncover this pattern). Can vocal measurements help us uncover some more interesting details in this group? We think they may, but this would need rigorously controlled recordings and sampling of the same individuals repeatedly. We have already mentioned the possibility that vocal variation is clinal in the group as well, but with such large amounts of variation in the frequency and temporal domains, this remains difficult to test.


“Clinal variation has been reported in Upucerthia dumetaria and in Upucerthia validirostris (the only two widespread Upucerthia in which such a pattern would be easier to detect). This morphological variation is apparent without any clear indication of vocal differentiation. This does not mean that vocal variation does not exist, but it indicates that despite fairly obvious differences in plumage coloration and measurements, vocalizations can be attributed to clearly delimited vocal groups (i.e., species in our view) which respond to within-group playback experiments but which ignore between-group playback trials. The existence of a morphological leap in a montane bird in concordance with a major geographical barrier such as a mountain is not surprising as has been widely documented in the literature on Andean birds.


“In sum, we do not see anything in Rheindt’s arguments to make us think that validirostris and jelskii/pallida should be considered as different species. Such a treatment would need to accept that they:


a) display by far the smallest genetic distance in the genus,

b) are the morphologically most similar taxa afforded species level rank in the genus with morphological differentiation equivalent to that within the other widespread species in the genus,

c) respond to playback of each other’s voice while other valid species ignore playback of parapatric and/or sympatric and rarely syntopic species, and

d) have morphologically identical notes.


“Finally, Rheindt implies that the lack of discussing the molecular study by Derryberry et al. (2011) in great detail in some way supports his notion that two species are involved. To the contrary, this molecular study demonstrates the tiny molecular gap between the taxa supporting our own conclusions. Moreover, sampling of Upucerthia in this family-level study was not detailed enough to allow us a detailed discussion, an expected consequence given the goals of this broad phylogenetic study.”


Comments from Nores: “YES. The combination of broad-scale morphological data plus playback experiments leave no doubt that treatment of merging the two species into a single species is required. However, their claim: “in the case of populations separated on isolated mountains, the same situation of allopatry would impede their assignment to the same species under the traditional view”, seems to be just the reverse. For example, in many extra-Andean mountains such as Sierras Pampeanas in Argentina and Tepuis in Venezuela, Ecuador and Colombia, there are several populations considered subspecies of Andean species under the traditional view. However, playback experiments or molecular analysis may indicate that they are different species.”


Comments from Jaramillo: “YES – I find this a tough one because as Frank notes, the fast jump (I don’t think it can be termed a cline, although it may be a step cline once more data is gathered from that region) between jelskii and validirostris in NW Argentina is clearly suggestive of a barrier in gene flow. The change in coloration is also abrupt. So we have linear dimensions as well as coloration suggesting that there is a barrier between two different creatures. By the way, I don’t know that the data is there to say there is a cline in jelksii, sample sizes at the higher latitudes are small, and perhaps this should have been done using a multivariate methodology rather than comparing linear measurements but that is a different topic. Thus far I am not convinced.

            “The issue that is more problematic is that there is no similar vocal step/jump between the two. There are complications in analyzing voices of these species as they are extremely variable: number of notes per bout, how closely spaced the notes are, and in my experience even the pitch is rather variable. Some jelskii can be low pitched and reminiscent of albigula in their sound. However if you drill down to the actual notes themselves, they are very simple in shape in validirostris/jelskii, sort of like upside down “U” s. How they deliver these notes is what varies, but the notes themselves are easy to assess, and they are quite different from the individual notes in albigula, saturatior, and dumetaria. In comparison to other species in the genus, indeed there are no obvious differences in the voice of validirostris and jelskii, although I leave the option open that a more systematic look at voice may find some differentiation. Even so, the birds themselves do behave as if they were the same thing based on playback experiments. It is true, positive response to playback is much less informative than negative response, but these two creatures are not allopatric, but their ranges meet and it is difficult to say that song is keeping them apart there. Although something is going on, otherwise we would not have the jump in morphology and coloration. I should note that over the years in Putre, Chile I have had intraspecific response to Upucerthia voices, although I have not made any systematic records of this. But I have been puzzled there when the wrong species has come in to playback (albigula and jelskii are sympatric there) with the caveat that they are tricky to identify visually at times, and maybe that was the problem, although I do not think so.

            “So I vote YES mainly because I find the vocal information hard to reconcile. Maybe we are giving the voice data too much weight, and not enough to the morphology and coloration?. An open question is wouldn’t we expect intermediate birds where these two meet if they are the same species? Is it just low sampling that keeps us from seeing these, or do they not exist and are these actually allopatric populations with the same voice? It would be very important to document if the two groups hybridize, or not, and what happens exactly in that intermediate zone? I am open to there being two very closely related, recently separated species with nearly identical voices. But to be consistent with how we have tended to treat voice in other species, I vote to lump, yet knowing what happens in that contact zone is key to figuring out this conundrum.”