Proposal (852) to South American Classification Committee
Recognize Scytalopus
krabbei
Effect
on AOU SACC classification: The addition of a new, Peruvian endemic, member of the Scytalopus
magellanicus complex.
Background: The tapaculo genus Scytalopus
has become the poster child for unrecognized diversity in the Neotropics. In
the early 20th century (e.g., Cory and Hellmayr 1924) only 16
species were recognized, this was reduced to only 9 (10, counting S.
indigoticus, which is now in genus Eleoscytalopus) by Zimmer (1939)
and Peters (1951). Now, nearly a century after Cory and Hellmayr, SACC
recognizes 43 spp., and new species are being described nearly annually. The
tropical Andes seem to be home of the highest species richness within the
genus, with strongly elevational stratification among species—as many as seven
species can share a slope from about 1000 m to treeline (usually around 3500 m);
along a slope, seldom do two closely related species occur, rather, each
elevational replacement is sister to an allopatric form, usually separated by
an intermontane valley. This pattern of allopatric replacements is, as one might
predict, most pronounced among the highest-elevation species, the members of
the S. magellanicus complex. This complex stretches from Colombia to
Tierra del Fuego, and comprises at least 16 well-defined genetic clades (and
probably more, with more sampling). In addition to genetic differentiation,
these clades are defined by vocal differentiation, something that aligns with
the general application among birds of the Biological Species Concept (perhaps
the most conservative of present-day favored species concepts), as has been
applied by recent suboscine work (e.g., Isler et al. 1998). Thus, specialists
studying the family have been churning out descriptions of new taxa with
regularity. The most recent publication to tackle the group is Krabbe et al.
(2020), which described three new species, all endemic to Peru.
Analysis: Of the three new taxa described in Krabbe et
al. (2020), one was actually a bit of a surprise to those who had encountered
it. It had been collected at first on the Cordillera Colán in Amazonas dept.,
Peru, then again at Unchog in Huánuco, Peru, and finally on Cerro Patricia on
the border of Amazonas and San Martín depts., Peru. In each case, the specimens
are easily distinguished by the presence of white feathers on the greater wing
coverts. Nevertheless, in each case, the specimens were cataloged as other
species (mostly S. altirostris), or as unidentified “Scytalopus sp.?”
with the white plumage regarded as a recurring plumage mutation. Cadena et al.
(2020) discovered that two specimens, both identified as S. altirostris, were not closely related to each other; advance
knowledge of this surprising find focused attention on the nature of variation
in all records attributed to that taxon. When vocalizations of “S.
altirostris” were surveyed across its range for the work finally published
in Krabbe et al. (2020), it was clear that there were two distinct voice types.
The accompanying phylogeny placed the white-winged birds on a branch sister to
the rather disjunct S. affinis (of the Cordillera Blanca and nearby C.
Huayuash in Ancash and Lima depts., respectively), whereas S. altirostris
(including the holotype of the taxon) was in a clade containing the S.
magellanicus complex otherwise comprising the taxa from southern Peru to
northern Argentina, and sister to S. frankeae.
Using
ancient DNA sequencing of toe pad samples, all specimens of this new species
showed the characteristic white on the greater wing coverts, meaning that this
character is actually a valid species specific one! This, combined with the
distinctive voice and phylogenetic placement make the species status of this
form unquestionable. The species was named S. krabbei by a subset of the
authors of the main paper to honor Niels Krabbe, who has been one of the
leading authorities of Andean Scytalopus taxonomy. The English name,
White-winged Tapaculo, draws attention to its most obvious field character.
Recommendation: I believe Krabbe et al. (2020)
have made a strong case for the recognition of S. krabbei, and recommend
that SACC include it in its list of Scytalopus. The suggested English
name White-winged Tapaculo highlights an relatively easily-seen field
character, something rare within the genus. I suggest that it also be adopted
by SACC.
Literature
cited:
Cadena,
C.D., A.M. Cuervo, L.N. Céspedes, G.A. Bravo, N.
Krabbe, T.S. Schulenberg, G.E. Derryberry, L.F. Silveira, E.P. Derryberry, R.T.
Brumfield, and J. Fjeldså. 2020. Systematics, biogeography, and diversification
of Scytalopus tapaculos (Rhinocryptidae), an enigmatic radiation of
Neotropical montane birds. Auk 137: xxx. https://doi.org/10.1093/auk/ukz077
Cory,
C. B., and C. E. Hellmayr. 1924. Catalogue of birds of the Americas.,
Part III. Field Museum of Natural History Zoological
Series, Volume XIII, Part 3.
Fjeldså, J., and N. Krabbe. 1990.
Birds of the high Andes. Apollo Books, Svendborg, Denmark.
Isler, M. L., P. R. Isler, and B. M. Whitney.
1998. Use of vocalizations to
establish species limits in antbirds (Passeriformes: Thamnophilidae). Auk 115:
577-59.
Krabbe,
N.K., T.S. Schulenberg, P.A. Hosner, K.V. Rosenberg, T.J. Davis, G.H.
Rosenberg, D.F. LANE, M.J. Andersen, M.B. Robbins, C.D. Cadena, T. Valqui, J.F.
Salter, A.J. Spencer, F. Angulo, and J. Fjeldså. 2020. Untangling cryptic
diversity in the High Andes: Revision of the Scytalopus
[magellanicus]
complex (Rhinocryptidae) in Peru reveals three new species. Auk 137: xxx.
https://doi.org/10.1093/auk/ukaa003
Peters, J. L. 1951. Check-list of birds of
the world. Volume VII. Museum of Comparative Zoology, Cambridge, Massachusetts.
Zimmer, J. T. 1939. Studies of Peruvian
birds. No. XXXII. The genus Scytalopus. American Museum Novitates number 1044.
Daniel
Lane, April 2020
Note on voting from
Remsen: Although I anticipate no problems, let’s formally
break this into “A” for species rank and “B” for adoption of the proposed name.
Comments from
Remsen: “A. YES. All data are consistent with recognizing this
as a new species. B. YES – perfect
name.”
Comments from
Areta: “A. YES.
I recorded this bird last year and had trouble in assigning it to
any know species until the eponymous Niels told me what was going on there.
Amazing! B. Good name, innocuous but accurate.”
Comments
from Robbins:
“A. YES, the combination of that unique white in the wing and voice make this
straightforward.”
Comments
from Bonaccorso:
“A very enthusiastic YES. Thanks, Krabbe et al! At
last a Scytalopus that anybody can tell apart!”
Comments
from Jaramillo:
“A. YES – clear-cut case. B. YES – to White-winged Tapaculo for the English
Name.”
Comments from Zimmer: “ A. YES, all data sets support the recognition of krabbei as a distinct species. B. YES to White-winged Tapaculo as
the proposed English name – so rare to have an appropriately descriptive name
for a Scytalopus!
“As an aside, I was struck by the overview of the S. magellanica complex in the Background
Section of this proposal, specifically, with the observation that “along a
slope, seldom do two closely related species occur, rather, each elevational
replacement is sister to an allopatric form, usually separated by an
intermontane valley.” This appears to be
the opposite of the situation found in species diversification among white-eyes
(genus Zosterops) in East
Africa. Zosterops, like Scytalopus,
is a speciose genus containing both highland and lowland representatives, whose
true species diversity was long underestimated by plumage-based
taxonomies. Among East Africa Zosterops, the most egregious failure of
a plumage-based taxonomy to reflect the species-level relationships and
phylogeny, involved six isolated montane populations that were long treated as
subspecies of one polytypic montane species, Z. poliogaster. The
incorporation of vocal and ecological data sets with recent genetic
investigations has revealed that not only are several of these montane populations
worthy of full-species status, but, that
most of them are more closely related to geographically proximate taxa with
differing habitat and elevation preferences than they are to other “sky island”
montane isolates, even neighboring ones.
They are, therefore, thought to have arisen independently as a result of
niche divergence, as opposed to through vicariant events resulting in the
fragmentation of an ancestral montane population.”
Comments
from Schulenberg:
“YES. I don't
think it's a great name - this bird is not white-winged in the sense of Xipholena
atropurpurea - but I don't have anything better to offer, and I gather no
one else does either.”
Comments from Pacheco: “A. YES. The treatment of S.
krabbei at the species rank seems to me justified for multiple reasons.”