Proposal (855) to South American Classification Committee
Recognize Scytalopus androstictus as a species
A: Accept Scytalopus androstictus as a species.
The delineation and ranking of Scytalopus taxa has undergone considerable change and remains problematic. Zimmer (1939) used only morphology to define taxa. Krabbe and Schulenberg (1997) included vocal data, ranking all forms with distinctive songs as species. This approach was consistent with the limited genetic material available at the time (Arctander and Fjeldså 1993) and has since been corroborated in full (e.g. Cadena et al. 2020). Later, three Brazilian forms, all genetically distinct and with diagnostic calls, but with songs that do not differ appreciably from those of relatives were described and ranked as species, first S. iraiensis (Marsh Tapaculo), whose song principally differs that of southern populations of S. speluncae/notorius (Mouse-colored Tapaculo) in the introductory notes (Bornschein et al. 1998), later S. diamantinensis (Diamantina Tapaculo) (Bornschein et al. 2007) and S. petrophilus (Rock Tapaculo) (Whitney et al. 2010). Note that the latter two species have songs are very similar to, or least overlap in most quantitative traits, with songs of S. pachecoi (Planalto Tapaculo), but both S. diamantinensis and S. petrophilus have diagnostic calls. The recognition by SACC of S. diamantinensis, in particular, generated much discussion (see AOS-SACC Proposals 329 on diamantinensis and 463 on petrophilus), but both were accepted after healthy debate.
Krabbe and Cadena (2010) described a new taxon androstictus and followed (albeit with hesitation) a rigid interpretation of the criteria of Krabbe & Schulenberg (1997) by ranking it as a subspecies of S. opacus because the two have fairly similar songs. Genetically, canus, opacus, and androstictus are each other’s closest relatives and form three distinct branches with pairwise differences in mtDNA exceeding 5%, being about equally distinct from each other. Although canus differs from the others in both morphology, song, and call, the diagnostic features of androstictus that separate it from opacus include only a white wing patch present in 10 out of 12 Ecuadorian males (but lacking in all three males from Peru), a substantially different call, and a song lacking the distinctive introductory notes, which are present in 19 of 23 songs of opacus analyzed (see Fig. 5 in Krabbe and Cadena 2010).
Krabbe et al. (2020) gave weight to four criteria in ranking Scytalopus taxa:
“(1) Populations are found in sympatry or parapatry along elevational gradients without evidence of interbreeding, thus maintaining their integrity because of reproductive isolation (Mayr 1942).
(2) Populations are vocally diagnosable. Contra Krabbe and Schulenberg (1997, 2003), who considered only vocal differences in song, we follow the broader approach by Whitney et al. (2010) by also including diagnostic calls.
(3) Populations are genetically distinct, as inferred by phylogenetic analysis of available genetic data revealing reciprocal monophyly. We expect that populations are more likely to be species if they have maintained DNA sequence divergence from other similar populations, but we apply no operational thresholds for recognizing species.
(4) Populations are morphologically diagnosable. Many universally accepted Scytalopus species fail to fulfill this expectation, but we include it for cases of morphological distinctness.
Here, we rank populations as species if they fulfill at least criterion 1, or the union of criteria 2 and 3, resulting in taxonomic decisions broadly consistent with those already in place for Scytalopus.”
Concerning criterion 1, opacus and androstictus are today separated only by 28 km of ridge immediately west of Loja city, and except for a 1 km stretch at 2400 m elevation at the cold and windy Cajanuma divide, no pass in this ridge is below 2500 m, which is just 400 m below the present lower elevational limit for them. The two almost certainly met during colder periods in the Pleistocene, yet maintained their integrity. As for criterion 2, the two are certainly vocally diagnosable, as they have strikingly different calls. Additionally, the song usually also differs. As for criterion 3, the genetic difference between them is 5.3 % in mtDNA, which is more than between some forms now presumed to live in sympatry (intermedius and macropus) or living in parapatry, replacing each other altitudinally (various members of the very recently evolved [S. femoralis] clade). Some populations of S. atratus, S. bolivianus, and S. parvirostris differ genetically more from each other, but these are expected to be split after further study of their vocalizations (Cadena et al. 2020). Even criterion 4 arguably applies, as 10 out of 12 males (10 out of 15, if Peruvian birds are included) can be distinguished by their white wing spot.
This leaves undecided the ranking of forms with distinctive calls but with little genetic or morphological differentiation, such as the population of S. spillmanni in the W Andes of Colombia (Krabbe et al. 2006). This and many other species of Scytalopus (such as latrans, acutirostris, schulenbergi, parvirostris, atratus, and speluncae/notorius) are still in need of further sampling and study.
To sum up, androstictus fulfils criteria 2 and 3, and arguably also criteria 1 and 4 of Krabbe et al. (2020) and thus should be ranked as a biological species. I therefore recommend that you vote yes to part A of the proposal.
B: Adopt the English name Loja Tapaculo.
The species occurs on the ridges separating the provinces of Loja and Zamora-Chinchipe in Ecuador, and the departments of Piura and Cajamarca in Peru. I suggest the name Loja Tapaculo, whence comes the type. S. opacus also occurs in Loja, but it has a much larger range (north to Colombia). The name Loja Tapaculo indicates a small range. S. opacus could keep the name Paramo Tapaculo.
As for the vernacular name, I also recommend a yes, but better suggestions are welcome.
Arctander, P. and Fjeldså, J. 1994. Andean tapaculos of the genus Scytalopus (Aves, Rhinocryptidae): a study of speciation using DNA sequence data. In: Loeschcke, V., Tomiuk, J., Jain, S.K. (Eds.), Conservation Genetics. Birkhauser Verlag, Basel, Switzerland, pp. 205-225.
Bornschein, M. R., Reinert, B. L., and Pichorim, M. 1998. Descrição, ecologia e conservação de um novo Scytalopus (Rhinocryptidae) do sul do Brasil, com comentários sobre a morfologia da família. Ararajuba 6: 3-36.
Bornschein, M. R., Maurício, G. N., Belmonte-Lopes, R., Mata, H., and Bonatto, S. L. 2007. Diamantina Tapaculo, a new Scytalopus endemic to the Chapada Diamantina, northeastern Brazil (Passeriformes: Rhinocryptidae). Revista Brasileira de Ornitologia 15:151–174.
Cadena D. C., Cuervo, A. M., Céspedes, L. N., Bravo, G. A., Krabbe, N., Schulenberg, T. S., Derryberry, G. E., Luis Silveira, L. F., Derryberry, E. P., Robb T. Brumfield, R. T. & Fjeldså, J. (2020). Systematics, biogeography and diversification of Scytalopus tapaculos (Rhinocryptidae), an enigmatic radiation of Neotropical montane birds. The Auk 137: xxx. https://doi.org/10.1093/auk/ukz077
Krabbe, N. & Schulenberg, T. S. 1997. Species limits and natural history of Scytalopus tapaculos (Rhinocryptidae), with descriptions of the Ecuadorian taxa, including three new species. Pp. 46-88 in Remsen, J. V. [Ed.] Studies in Neotropical ornithology honoring Ted Parker. Ornithological Monographs 48.
Krabbe, N., Florez, P., Suárez, G., Castaño, J., Arango, D. & Duque, A. 2006. The birds of Páramo de Frontino, Western Andes of Colombia. Ornitología Colombiana 4: 37-48.
Krabbe, N. and Cadena, C. D. 2010. A taxonomic revision of the Paramo Tapaculo Scytalopus canus Chapman (Aves: Rhinocryptidae), with description of a new subspecies from Ecuador and Peru. Zootaxa. 2354: 56-66.
Krabbe, N. K., Schulenberg, T. S., Hosner, P. A., Rosenberg, K. V., Davis, T. D., Rosenberg, G. H., Lane, D. F., Andersen, M. J., Robbins, M. B., Cadena, C. D., Valqui, T., Salter, J. F., Spencer, A. J. & and Fjeldså, J. 2020. Untangling cryptic diversity in the High Andes: revision of the Scytalopus [magellanicus] complex (Rhinocryptidae) in Peru reveals three new species. The Auk 137: xxx. https://doi.org/10.1093/auk/ukaa003
Whitney, B.M., Vasconcelos, M.F., Silveira, L.F., Pacheco, J.F. 2010. Scytalopus petrophilus (Rock Tapaculo): a new species from Minas Gerais, Brazil. Revista Brasileira de Ornitologia 18: 73-88.
Zimmer, J.T. 1939. Studies of Peruvian birds. No. XXXII. The genus Scytalopus. American Museum Novitates 1044.
Niels Kaare Krabbe, 23 April 2020
Comments from Robbins: “YES, based on the distinctive calls and the relatively substantial genetic differentiation from closely related taxa.”
Comments from Areta: “YES. The calls of androstictus differ dramatically from those of opacus (and canus). Songs of androstictus differ from opacus not only by the lack of the short trilled introductory notes, but also by their more ticking sound (although this may demand more precise measurements, it sounds more ticking to my ear) and their sometimes clearly ticking ‘introductions’.”
Comments from Bonaccorso: “YES. Differences in genetics and voice are consistent with a new species.”
Comments from Jaramillo: “A. YES – A tad more confusing than the previous ones, but convincing. Both calls, and genetic distance. B. YES – Loja Tapaculo works.”
Comments from Zimmer: “A. YES to recognizing androstictus as a distinct species. The sum of evidence from multiple data sets (vocal, morphological, genetic) supports this recognition. There is substantial precedent in other suboscine species-complexes for calls being better indicators of relatedness than primary songs, so, using that yardstick, the vocal evidence seems rock solid. B. YES to applying the English name of Loja Tapaculo, in recognition of the type locality for the species, a common naming practice in this morphologically conservative group.”
Comments from Stotz: “A. YES. I think the genetic and vocal differences are sufficient to accept androstictus as a distinct species. B. YES. Loja Tapaculo seems like a good choice for an English name.”
Comments from Stiles: “YES: calls and genetics clearly indicate that androstictus should be accorded species rank.”
Comments from Pacheco: “A. YES. Considering the taxonomic decisions already existing for Scytalopus, the arguments used to defend the species ranking for the present taxon seem to me to be consistent.”