Proposal
(475) to South
American Classification Committee
Recognize
Myrmeciza palliata as a separate
species from Myrmeciza laemosticta
Three species of “Myrmeciza” antbirds are
currently recognized in the laemosticta complex,
namely M. laemosticta, M. nigricauda, and M. berlepschi. These species have had an unstable taxonomy, with
sexes of single species treated in separate taxa, or members classified in
different and often distantly related genera (see Robbins & Ridgely 1991,
Zimmer & Isler 2003). Currently, only
M. laemosticta is polytypic, with two
subspecies: the nominate subspecies from lower Central America (NW Costa Rica
to Darién in E Panama) and palliata
from the Colombian and Venezuelan foothills of inter-Andean valleys (Wetmore
1972, Zimmer & Isler 2003). The taxon palliata
includes synonymized forms bolivari
and venezuelae (Robbins & Ridgely
1991) and has never been considered a separate species.
Observations
and recordings by B. Whitney and A. Cuervo (published in the Colombian Andes
Sound Guide; Alvarez et al. 2007) of the then-unknown loudsong of M. l. palliata from the Magdalena valley
were indicative of their distinctiveness and degree of differentiation with
respect to the loudsongs of M. l.
laemosticta. Chaves et al. (2010) recently evaluated species limits in the laemosticta complex and investigated
whether M. l. palliata merited
elevation to species rank. Specifically, they conducted a quantitative analysis
of vocal variation in male songs and a qualitative assessment of variation in
calls and female songs and calls, coupled with a phylogenetic hypothesis for
the group based on sequences of a mtDNA gene.
Fourteen
vocal traits in a total of 42 individuals of the complex plus M. griseiceps were analyzed
statistically. M. l. palliata is
indeed vocally diagnosable from any other species, and different from M. l. laemosticta in three vocal
characters. A multivariate analysis of songs showed that each taxon differs
significantly from the others: M. l.
palliata is vocally divergent from M.
l. laemosticta and closer to, but distinct from, M. nigricauda. Vocal results were consistent with the ND2 gene
tree, which showed a highly supported clade for the laemosticta complex with the four taxa forming a polytomy (i.e. no
support for a sister relationship between laemosticta
and palliata), and branches
leading to each taxon were relatively long, thus indicating a comparable time
of isolation. Thus, pairwise genetic distances were nearly the same among the
four taxa.
Chaves
et al. concluded that M. l. laemosticta and
M. l palliata should be treated as
distinct species under criteria of diagnosability and (inferred) potential
reproductive isolation. Vocal variation indicates that M. l. palliata merits elevation to species rank following the
standards for allopatric populations in antbirds (Isler et al. 1998), and
genetic variation indicated an independent history of evolutionary isolation
roughly congruent with the divergence among currently recognized species in the
group. I encourage all to read the paper for further details on methods and
results and to examine vocalizations in xeno-canto.
The
English name Magdalena Antbird is recommended for M. palliata (Chaves et al. 2010).
This name was previously used by Cory and Hellmayr (1924) for Formicivora grisea hondae. Meyer de
Schauensee (1950) didn’t follow Cory and Hellmayr’s name for F. g. hondae and used “Honda Ant-Bird”
instead. In both publications, Pale Antcatcher was used for M. laemosticta palliata. The English
names proposed for these subspecies have no tradition of usage (i.e. only used
in these publications) and taxonomic nomenclature rules do not apply for
English names.
Recommendation: I recommend a YES vote to recognize “Myrmeciza” palliata as a separate species from “Myrmeciza” laemosticta and to adopt the
English name Magdalena Antbird for M.
palliata.
Literature
cited
Álvarez, M., V. Caro, O. Laverde & A. M. Cuervo. 2007.
Guía Sonora de las Aves de los Andes Colombianos. Instituto Alexander von
Humboldt & Cornell Laboratory of Ornithology.
Chaves, J. C., A. M. Cuervo, M. J. Miller, & C. D.
Cadena. 2010. Revising species limits in a group of Myrmeciza antbirds reveals a cryptic species within M. laemosticta (Thamnophilidae). The
Condor 112: 718-730. http://www.museum.lsu.edu/cuervo/pubs_files/Chaves_etal.Condor.2010.pdf
Meyer de Schauensee, R. 1950. The birds of the Republic of
Colombia. Caldasia 5 (24): 645-871.
Other
references in the SACC reference list or in the Chaves et al. paper.
Andrés M. Cuervo, December 2010
Comments from Zimmer: “YES. As far as I can tell from listening to vocal samples of palliata (which I don’t know in life) versus those of laemosticta, which I have recorded extensively in Costa Rica and Panama, the two taxa are diagnosably different (vocally) to an extent consistent with species-level recognition in Thamnophilidae. The vocal and genetic analyses of Chaves et al. (2010) would seem to support that conclusion. “Magdalena Antbird” seems appropriate as an English name for palliata.”
Comments from Thomas
Donegan:
“Summary: Chaves et al. (2010) demonstrate clearly that palliata should not be treated as part
of the same species as the Dull-mantled Antbird M. laemosticta. However,
they do not deal adequately with the elephant in the room. Esmeraldas Antbird M. nigricauda (of the West Andes foothills) and palliata (Central
and East Andes foothills) are vocally almost identical, have similar habitat
requirements and elevational ranges on adjacent mountain ranges and were
historically treated as conspecifics.
Andrés Cuervo’s proposal does not discuss whether palliata is a good species with respect to nigricauda nor does it note that the vocal differences fall below
that typically used as a benchmark for species rank in antbirds. Chaves et al. (2010) briefly discuss the
point, but their discussion is inconsistent with the data presented and
unconvincing.
“In January 2003, I made what I understand to be the first known
Colombian recordings of palliata in
Cerro de la Paz, Santander, Colombia (http://www.xeno-canto.org/recording.php?XC=24335)
and then compared sonograms of this with those of M. nigricauda and M.
laemosticta. At one point, I
prepared a short note with a view to publication, but this was not developed
further when I heard that Chaves, Cuervo and Cadena were conducting their own
more detailed study, a few years ago.
Chaves et al. (2010) have spent a lot of time and effort investigating
the situation further and speak to their own history of study in this
group. They should be congratulated for
dealing with the laemosticta / palliata issue in a diligent way. The molecular data is also very
interesting. However, the authors are
not persuasive in concluding that palliata
is a separate species from nigricauda
based on vocal differences. The
reasons for this are set out below.
“Vocal issues
“Isler et al. in their various papers have generally adopted a
“three diagnosable differences” test for loudsongs in assessing species rank
for antbirds. Chaves et al. (2010) do
well to consider whether this test is appropriate for this particular group of antbirds. It has recently been shown that sympatric
species of suboscine groups may show lower levels of diagnosable differences in
loudsong than the traditional benchmark of three differences. Chaves et al. (2010) call for a “2
diagnosable differences” test to be applied for these Myrmeciza based on the differences between nigricauda and berlepschi. Some preliminary results with other Myrmeciza I am currently studying
vocally would also support this more liberal approach, as do studies of
sympatric members of the Warbling-Antbird group. However, despite what is said in Chaves et
al. (2010), it is a big stretch to conclude that palliata and nigricauda meet
even this “two differences” test.
“The authors do not appear to have actually elucidated two differences
in loudsong between palliata and nigricauda. Their Table 1 (p.720) asserts the two
differences to be in “Note shape” and “Note structure”. Those ‘two’ variables appear on their face to
be the same thing. The authors list all
vocal variables that were studied in Appendix 2 (p. 729). The variable “Note structure” is described
but “Note shape” is not mentioned. In
Appendix 3 (p. 730) the authors go on to describe the nature of the differences
shown, and cite differences in both “Note shape” (the same term not defined
elsewhere) and “Change in note structure” (a variable not mentioned in Table 1
for this species pair, but which is defined in Appendix 2). The discussion of the differences between nigricauda and palliata in Appendix 3 refers to supposedly diagnosable differences
referable to “Change in note structure” (although more on that below) but does
not mention overall diagnosable differences in note structure.
“As can be seen from their Figure 2 (p. 721) and other recordings
on xeno-canto, both palliata and nigricauda give inverted chevron shaped
notes and also more “rounded” inverted-chevron-shaped notes. Some of these note shapes are given in a
different order within songs in the sonograms presented in Figure 2 and some of
them are skewed differently. However,
note shape should only be treated as a diagnosable difference if none of the
notes of the two populations are similar.
It is clear that both nigricauda and
palliata are capable of giving notes
of the same shape: they just do so at different points in time in the sonograms
presented. The only difference that the
authors describe is the order in which the notes of particular structure are
delivered – i.e. a difference in “change in note structure”, or, more
accurately “The note structure of certain notes at a particular point in time
or segment within the song”, not actually “Note structure”. This single
vocal difference should not be double-counted.
“Even then, Chaves et al. (2010)’s description of changes in note
structure does not concord with available recordings. The sonograms of these taxa on xeno-canto
show considerable variation in note shape of both M. nigricauda …
http://www.xeno-canto.org/browse.php?query=myrmeciza
nigricauda&pagenumber=&order=taxonomy&view=3
… and
“M. palliata”
http://www.xeno-canto.org/browse.php?query=laemosticta
cnt:colombia&pagenumber=&order=taxonomy&view=3
“Appendix 3 accurately discusses the subjective differences between
the sonograms shown in Figure 2, but it does not take account of individual
variation in these birds. The authors
describe palliata songs as
constituting three segments. Supposedly,
in the first segment, “notes of M.
nigricauda are rounded, those of M.
l. palliata are slurred up–down”.
However, XC3870 of M. nigricauda is
as up-down in the first segment as various palliata
recordings. In the third segment,
the authors claim that “both taxa emit rounded notes (partially modulated in M. nigricauda). However, several recordings of palliata do not show any such “third
segment”: examples are XC10725, XC16311 and XC18154. One of these recordings was cited in the
paper as being part of the sample studied.
The authors also conclude that in recordings of nigricauda, note shapes “change
from rounded to partially modulated to rounded again”. However, sonograms of nigricauda on xeno-canto (none of which the authors studied)
include more variety in note shape, with examples where the third segment
involves a sharp up-down stroke (XC18884), more rounded inverted chevron
(XC30289), or down stroke with a small rising initial tail (XC58961). The methodology (p. 720) asserts that the
authors “examined qualitative characters through a blind inspection and
grouping of printed sonograms followed by an assessment of whether the
groupings matched the populations under study”.
But their definition of the differences in “change in note structure”
between these taxa do not facilitate the blind allocation of available
recordings to particular species. More
detailed and convincing analysis on this issue is warranted. Given that there is a larger sample available
on xeno-canto, it would be better to include these additional recordings in
analyses.
“The authors also mis-describe the results of their multivariate
analysis as regards nigricauda and palliata. They state as follows: “Discriminant function
analysis of songs of the four taxa in the M.
laemosticta complex revealed that each taxon’s group centroid differs
significantly from the others (Wilks’ L = 0.003, df = 36, P < 0.0001). The
analysis classified correctly 100% of individuals to their respective
population designation (Table 3; Fig. 4), demonstrating that M. l. laemosticta, M. l. palliata, M. nigricauda,
and M. berlepschi are all vocally diagnosable with respect to each other
in multivariate space.” (p. 721). This
statement may be correct as regards diagnosis as between most of the species
pairs studied. However, as regards nigricauda and palliata it is highly misleading.
The two taxa do not appear to be diagnosable based on quantitative
measures. The authors cite Table 3 (p.
724) and Figure 4 (p. 724) for the proposition that “100% of individuals”
(including of palliata vs. nigricauda) could be classified correctly.
However, in Figure 3 (p. 723), nigricauda
and palliata overlap for all vocal
variables. Table 3 (p. 724) shows the
weight given to the variables in the analysis; and in Figure 4 (p. 724), palliata and nigricauda cluster together and would not appear diagnosable in the
(x=10-11, y=-12 to -10) part of the range.
The authors cite a Wilks lamda test, but that compares the statistical
significance of differences between centroids, not dealing with
diagnosability. To consider
diagnosability using multivariate analysis, one should demonstrate that recorded
values for the two groups fall either side of a curve or line, depict 95% or
higher ellipsoids on the diagram which should not overlap or carry out other
statistical tests. Figure 4 shows palliata and nigricauda clustering together, so it is doubtful that those sorts
of analyses would show diagnosability.
“Assuming that the authors were inadvertent in asserting that palliata and nigricauda are fully diagnosable in multivariate space, and given
that there are no diagnosable differences in the quantitative variables, we are
considering here only subjective differences in note shape. When comparing those to differences between
sympatric taxa, it should not be only the existence
of a difference that is relevant, but the degree
and nature of the difference. The
authors consider the vocal differences between palliata and nigricauda
to be similar to those between berlepschi
and nigricauda, which are sympatric. However, recordings of berlepschi show more fundamental differences in “note
structure”. M. berlepschi recordings involve down strokes, with only a tiny
rising “tail” in some instances and no significant “change in note
structure”. See Figure 2 (p. 721) and
also other recordings available on xeno-canto:
http://www.xeno-canto.org/browse.php?query=myrmeciza
berlepschi&pagenumber=&order=taxonomy&view=3
“In contrast, both palliata and
nigricauda songs consist of a series
of up-down strokes or “chevrons” of varying shape. As discussed above, perhaps only the “second
segment” shows diagnosable differences in note shape. The degree of those differences is not very
impressive compared with those between nigricauda
and berlepschi and are not
accurately described by Chaves et al. (2010).
“Finally, the authors refer to differences in call. Although this is not analysed in detail,
various examples of sonograms of calls are presented in Figure 5 (p. 724). The authors’ selection of published sonograms
is quite surprising. Similarly
structured calls do not appear to have been presented. Chaves et al. (2010) show the palliata call being a flat rasp, with
that of nigricauda being a very
different up-down stroke. However,
another of my recordings, XC31829 (and also XC10724 by Nick Athanas)
are of calls of palliata and they are
up-down strokes, with much more similar note shape to the sonogram of the call presented
by Chaves et al. (2010) of nigricauda. The calls of nigricauda and palliata sound
rather similar, with the call of nigricauda
perhaps being a little raspier.
“A conservative approach under a comparative BSC approach of the
nature adopted in Remsen (2005), Helbig et al. (2002) and similar papers would
therefore be to lump palliata with nigricauda on the basis of the vocal
data presented.
“Sampling gaps
“The authors have overlooked to study some very interesting and
important specimens. It has never been
suggested that laemosticta, palliata or nigricauda exist in sympatry and Chaves et al. (2010) do not
suggest this either. However, the three
forms occur in very close proximity in the central to northern section of the
West Andes and surrounding region. Some
of them may indeed be sympatric or parapatric.
The authors do not discuss whether or not the taxa intergrade in this
region.
“The closest materials studied by Chaves et al. (2010) for laemosticta are from Panama, palliata from
the northern Central Andes and nigricauda
from the southern-central part of the West Andes. M.
nigricauda is generally not considered to extend further north in range
than the locality sampled by the authors in major texts. However, the literature may not be correct in
this respect. Project Biomap (www.biomap.net) data include a specimen of nigricauda from the Baudó mountains in
Chocó department (ANSP 147226) and another from Remedios, Antioquia in the
northern foothills of the Central
Andes (Colegio San José, Medellín, 0021B).
I have not seen these specimens or any photograph of them, but per
information on Biomap, the Remedios skin’s identification was confirmed by
Tomás Cuadros who noted that it represented a significant range extension.
“Based on these specimens, M.
nigricauda may range further north and east than is generally thought and
could be sympatric or parapatric with M.
(x.) palliata. Or it may not if
these are database or identification errors. The Baudó specimen, whatever it
is, falls in an important sampling gap.
There are now several lower elevation localities in the northern West
Andes foothills and Baudó mountains that are safe to study for sound recording
or other field studies. There is a
specimen of palliata which one of the
authors (Andrés Cuervo), Paul Salaman and myself collected in 1999 from the
northern end of the Central Andes below Anorí (close to Remedios) which is
close to these other localities, and this one was sampled by the authors. Chaves et al. (2010) should have studied the
other specimens mentioned above before concluding that palliata and nigricauda are
two species. If palliata and nigricauda
are sympatric and do not intergrade then they must be split, but the specimens mentioned above must first
be studied to confirm whether or not this is the case.
“Plumage
“Plumage differences are notable in the context of Thamnophilidae,
with differences in the mantle colour and throat pattern of males and wing bars
of females. However, these are not so
great such that the two forms were historically treated as conspecifics,
including as recently as by Hilty & Brown (1986). Certainly, palliata is closer in plumage to laemosticta than it is to nigricauda. It would be nice to see some data on biometrics
before concluding that phenotype supports the split of palliata from nigricauda and
the authors do not justify this split with regard to plumages.
“Molecular data
“One could also treat palliata
as a species because nigricauda would
otherwise be paraphyletic based on the molecular data and applying phylogenetic
species concepts. SACC has accepted some
splits in the past where there is paraphyly but little vocal support (e.g.
Ecuadorian Thrush, although the disjunct distributions were also relevant there). Genetic differences (7%) are pretty
impressive and more or less equal as between laemosticta, nigricauda and palliata. On the other hand, the laemosticta to palliata node
is not very strongly supported (0.73 / 61) and there are “good” species that show
greater intraspecific mtDNA variation than these.
“Conclusion
“Chaves et al. (2010)’s vocal data strongly support moving palliata from laemosticta to nigricauda
but do not support splitting palliata from
nigricauda. At least, it would be
sensible to take the following steps before making this split: (i) studies of
voice, the specimens referred to above, and molecular samples from the “gap” in
the northern West Andes and Baudó; (ii) a more convincing study and accurate
description of the differences (if any) in what I would term “The note
structure of certain notes at a particular point in time or segment within the
song”; (iii) a study of differences in the calls involving comparison of more
appropriate examples, a larger sample and statistical analysis; and (iv) more
information on the strength of molecular support for palliata plus nigricauda not
being monophyletic. Splitting palliata from nigricauda may be warranted (particularly if they are sympatric)
but it may not be. I just don’t
know. In the absence of the information
mentioned above, I would suggest a prudent course of action would be to reject
this proposal for the time being and treat palliata
as a subspecies of nigricauda. M.
nigricauda was described before palliata
(1892 vs. 1917) so the former name has priority, resulting in no change
being necessary to the SACC list.
“These criticisms are presented with a heavy heart – not least
because the last thing that Colombian ornithology needs at the moment is
another argument. However, these are
genuinely held concerns about the methods, discussion and new taxonomy in
Chaves et al. (2010)’s paper. The SACC
ought to be made aware of these concerns.
I would though warmly welcome any observations that the authors or
others may have in response to these comments.”
Comments from Bret Whitney: “I was a formal reviewer of the Chaves et al paper, and accepted it with minor revision, which objected mainly to their too-strict interpretation of the “three-character yardstick” as it was presented in Isler et al. (1998), and it was toned-down for publication. I think Thomas Donegan has also adopted an overly rigid interpretation of the “three-character yardstick”: we clearly stated that, for some groups, especially those for which other data sets provided support for significant divergences, less than three characters might be appropriate. I greatly appreciate Donegan’s criticisms, based in part on appropriate data not used by Chaves et al.; they are generally well-formulated and reasonable, and I find the bit about the geographic proximity of the three forms to be a sticking point, worth a focused trip to record and collect some specimens in an apparent, or at least potential, contact zone. That said, the Islers have formulated an objective and convincing test for the diagnosability of male loudsongs (albeit from a somewhat different sample than that employed by Chaves et al.), and on that basis I am willing to accept that, until further field collecting can be conducted, and a larger sample of vocalizations analyzed, the best course forward is the split of palliata and nigricauda. At present, I consider that decision an advancement in our understanding of the taxonomy of this poorly known complex, but it is always subject to revision should further collecting and analysis point to a different arrangement. To Donegan’s “heavy heart”, I suggest that ornithologists knowingly sharing a focused interest in the same groups of birds, and especially those gathering complementary data, make an effort to collaborate to produce the best publication, or set of publications possible. Then it’s left to the rest of us, who know a lot less about most of these individual situations, to try to make the best of the best.”
Additional comments from Andrés Cuervo,
Daniel Cadena, Juan Camilo Chaves and Matt Miller: “We welcome the
comments offered by Thomas Donegan on our Myrmeciza
laemosticta paper in which he questioned our recommendation of elevating M. l. palliata to species rank (a
hypothesis people started to think about ever since Bret Whitney obtained the
first recordings of songs of palliata
in Colombia in 1992) by pointing out that this taxon could be rather treated as
a subspecies of M. nigricauda based
on song similarity.
“To reach the conclusion that
the divergent taxa nigricauda and palliata are nothing else but
populations of the same biological species, one would have to ignore complementary evidence in
current existence and propel vocal similarity as the sole basis for that
interpretation. As Donegan points out, multiple lines of evidence should be
considered including better sampling in areas of potential geographic
contact and examining more vocal data than what we had at hand by mid 2008. We
believe this would be very worthwhile. Potential intergradation, which would
eventually support a lump between nigricauda
and palliata, when based on
inexistent data is mere speculation at this
point. Thus, we cannot comment on this more other than to say that
complementary studies and new specimens and recordings would be desirable. For
the purpose of evaluating this proposal we are left with the available vocal
and molecular data. We assume that the important baseline taxonomic and
distributional work by Robbins and Ridgely (1991) is being taken into
consideration as well.
“Regarding Donegan’s specific
criticisms, we accept up front that the qualitative differentiation between the
samples of palliata and nigricauda studied by Chaves et al.
could be subtler than we surmised and that we could have done a better job at
characterizing it verbally. However, an independent assessment by Mort and
Phyllis Isler led to the conclusion that songs of these taxa can indeed be
diagnosed qualitatively. The Islers went a step further to suggest that female
songs are also likely diagnostic. We did not emphasize the latter finding in
the paper much owing to what we thought was a reduced sample size.
“The multivariate statistical
analysis (and the genetic analysis, for that matter) should be taken as a
complement to the “yardstick” approach based on individual diagnostic features.
This analysis specifically seeks to derive composite variables that summarize
vocal variation and tests whether predefined groups can be discriminated by
variation in the data. These results are summarized in the paper’s Fig. 4 and
do reflect that quantitative vocal differentiation exists between palliata and nigricauda, although there is marginal overlap. However, the
decision of whether taxa are vocally diagnosable should not be based solely on
a cursory examination of this graph (which does not show other dimensions of
the discriminant function). More telling is the fact that nearly all recordings
were correctly classified by our discriminant function to their respective
taxon. Note we say nearly all because following Donegan’s criticism we have
reanalyzed our data and have to admit we found a mistake: the truth is that all
nigricauda recordings but one were
assigned to nigricauda (the other was
assigned to palliata), and all palliata recordings but one were assigned to palliata (the other was assigned to nigricauda). We thank Donegan for
leading us to realize a mistake crept in to our paper and we stand corrected.
Regardless, the results of the DFA suggesting differentiation are complementary
to the gold-standard methodology to establish species limits in antbirds (M.
Isler, P. Isler, B. Whitney), which is based on diagnosability in individual
traits (the issue discussed in the paragraph above). In any event, we expect
that as more recordings become available and more vocal types are compared, we
will get a more robust idea of the magnitude of vocal differentiation and its
biological implications and we do encourage further work on this system.
“Donegan states that we
should have studied a number of museum study skins listed in the Project Biomap
database before concluding that palliata merited species rank, but we note that: (1) most of the relevant
specimens (e.g. from the Baudó mountains) were indeed examined in a careful
review of the complex by Robbins and Ridgely (1991) – except one male from
Mutatá, NW Antioquia (J. Haffer specimen at ICN) that is inseparable from palliata specimens,
(2) the Biomap’s record from Remedios, NE Dept. Antioquia, turned out to be a
misidentified specimen (we have determined it is not even a Myrmeciza of this group but a male Cercomacra tyrannina), and (3)
independent of the inclusion or not of an analysis using specimens in our
study, the results from the vocal and genetic analysis are verifiable and we
think that the conclusions are sound.
“In sum, we suggest that even
if every point raised by Donegan was correct, then the information available
taken as a whole indicates that palliata
and nigricauda are differentiated
lineages that have been evolving independently to the extent that the inferred
potential reproductive isolation is likely. Direct tests of
such a hypothesis obviously require additional fieldwork, but the current data
are consistent with reproductive isolation of the two taxa, not the reverse. A
separate proposal (or better, a new, more comprehensive study) based on current
or new information for merging palliata
with nigricauda could be presented
elsewhere or to the consideration of this committee following formal analyses.
Consequently, we think that the most conservative hypothesis of species limits
in this group at this point is to maintain palliata
as a separate species from any other taxa of this complex.”
Additional comments solicited from Mort and Phyllis Isler: “In response to Thomas
Donegan’s thoughtful comments and the Acting Chair’s request to consider his
comments, we undertook an independent review of the vocal characteristics of Myrmeciza laemosticta palliata
(henceforth palliata) and M. nigricauda (henceforth nigricauda).
“Procedure: Mort examined spectrograms and extracted a
typical loudsong or multiple loudsongs if there was obvious variation,
including what appeared to be male and female songs, from every available
recording of palliata (n =10) and
every available recording of nigricauda
from Colombia and a random sample of nigricauda
recordings from Ecuador (n = 11, locations available on request). Recordings were allocated to taxa on the
basis of recordists’ identifications and geography. 39 loudsongs in all were extracted. Each was printed on a page with no
identifying data that were hand written on the backside of the page.
“The unidentified loudsongs
were given to Phyllis who had not yet read the Chaves et al. 2010 paper and had
no idea of the results. She was asked to
sort them into groups on the basis of qualitative characteristics and to
identify the distinctive characters that she used.
“Phyllis sorted the 39
loudsongs into two primary groups and five subsets. After she finished, we turned the pages over
to check the taxon. The two primary groups corresponded to palliata and nigricauda,
i.e., every loudsong was sorted correctly to taxon (100 percent). The loudsongs of nigricauda were further sorted into two subsets, the smaller of
which (n = 3) was later identified as a female loudsong, identified as such in
one recording. The loudsongs of palliata were sorted into three
subsets. Again a small (n = 5) subset
was identified as the female loudsong.
The other two subsets of palliata
differed only in the presence or absence of a high-pitched terminal note.
“Phyllis stated that she
used two characters to distinguish the two primary groups: (1) differences in
note shape and (2) differences in the sequence of change of note shape. With regard to the latter, she pointed out
that in one group the note change was gradual and subtle whereas in the other
group the note shape change was abrupt and substantial. The sequential placement of different types
of notes is independent of their presence or absence, and in our 1988 and
sequential papers, we have treated them as such. Although Phyllis’ description of change in
note shape differed somewhat from that of the paper, the independent “blind”
test supported the finding of the paper of a difference in two distinct qualitative
characters between palliata and nigricauda.
“Moreover, based on our
brief review, it appears that other vocal distinctions between palliata and nigricauda will be found in future studies. Principally, despite the small samples, it
seems certain that female loudsongs differ diagnostically from male loudsongs
and that female loudsongs differ between the two populations at least as much
as males, and probably more. The authors
describe differences in female loudsongs, but conclude that sample sizes are
too small to include them as characters in the diagnosis. We understand this conservative position, but
we would have given them more weight in the analysis as a second type of
vocalization because of the apparent consistency of the female loudsongs that
we see in our (slightly larger) samples.
Unfortunately, female loudsongs illustrated in the paper (Fig. 6 which
does not identify sources) do not seem to typify (represent central tendencies)
female loudsongs in our inventory that appear to differ somewhat more
dramatically between the two taxa.
Because female loudsongs were not included in the analysis, in our
opinion the statement in the paper that evidence is provided that two
characters may be sufficient to support species status is not supported by this
study. (By the way, we treat the three
diagnostic vocal character yardstick as a “point of reference, not a
requirement” [Isler et al. 1998], and in principle we would not object to a
strong case for two character finding.)
“Finally, beyond note shape
characteristics, we observed visually that pallida and nigricauda loudsongs appear to differ in note frequency, in
particular the frequency of the highest point in the note (peak
frequency). Consequently, we measured
peak frequencies of the initial note and the middle (central in time) note of
samples of palliata (n = 10) and nigricauda (n = 11). Peaks of palliata
notes started lower and increased, whereas peaks of nigricauda notes started higher and typically decreased in the
central notes of the vocalization. The
peak frequency of initial palliata
notes was 4157–4958 Hz (mean 4157 ± 235)
and of nigricauda 5041–5809 Hz (mean 5372 ± 271), although there is a
recording in our collection identified as Myrmotherula
schisticolor by the recordist but which appears to be nigricauda in which the peak of the first note is 4507 Hz. We also
computed the difference in peaks between the initial and middle notes. Peaks of palliata
notes increased from 184–635 Hz (mean
+442 ± 140), whereas those of nigricauda
decreased from 33–317 Hz (mean -202 ±
116) excluding an example in which the first note was lower pitched than the
second note and therefore slightly lower pitched (33 Hz) than the middle
note. We do not present these
preliminary data as a formal diagnosis, but they provide support to the conclusion
that male loudsongs of the two populations are distinct.
“Thomas Donegan also raises
issues regarding the multivariate analysis, differences in calls, geographic
distribution, plumage distinctions, and the molecular analysis presented in the
paper. The authors have responded to
most of these comments, and all agree that additional studies of the complex
would be useful.
“In summary, we recommend
that the committee accept the authors’ recommendation that Myrmeciza palliata be considered specifically distinct on the basis
of vocal differences between it and the other three species in the
complex. We conclude that two distinct
qualitative characters distinguish male loudsongs and may be supported by
differences in quantitative frequency measurements. Furthermore, differences in
female loudsongs, unevaluated in the paper, appear certain to provide
additional evidence that palliata and
nigricauda have evolved to species
status under the Biological Species Concept.”
Additional comments from Thomas Donegan: “The Islers have done
considerable work on my point (ii) above: (study of qualitative vocal
differences). There are apparently
diagnosable differences in the second section of the song as per my comments
above; and the Islers have now also come up with a further “change in note
structure” difference that Chaves et al. (2010) did not elucidate. Based on that study, the nigricauda / palliata split is supported. Bret Whitney nicely summarises the reasons
for doing this.
“It is pleasing that the authors have looked into
some of the records at range extremities.
When I heard of the Isler study last week, I also decided to look
further into these issues, obtaining a photo of the “nigricauda” specimen at Colegio San Jose supposedly identified by
Cuádros (new catalogue number CSJ-a 2219).
It is indeed of a male Cercomacra parkeri/tyrannina,
probably the latter based on elevation.
The curator is now correcting their database and labels. As noted in my earlier comments, the
specimens needed to be checked before coming to any conclusions! Separately, Reserva Natural de Aves “Las
Tangaras” in the northern West Andes may be an ideal candidate locality for
future studies, as it lies between known localities for nigricauda and palliata in
the northern West Andes. There are no
records of these birds there to date in the few studies that have taken place,
only M. berlepschi in lower elevation
forest below the reserve. That locality
deserves further study for these birds.
“One response to Bret Whitney’s comments: the
discussion set out above was not based on a rigid interpretation of the “three
characters” yardstick, but on the authors only describing a single difference
and not describing it in a manner consistent with the sample. The Islers have now come up with two
better-defined diagnosable qualitative differences in loudsong, which are
consistent with available recordings.
The Chaves et al. “two differences” yardstick is consistent with studies
of Hypocnemis (Isler et al. 2007) -
assuming the observed differences in call stand up to analysis. Moreover, it may be supported once a
forthcoming publication on some other Myrmeciza
including Myrmeciza goeldii /
melanoceps is out. In a study of
these and related species, including analysis of over 140 loudsongs for each of
goeldii and melanoceps and tens of other vocalisations, there would appear to
be only a single diagnosable difference in loudsong – also in “the note
structure of certain notes at a particular point in time or segment”. This pair is also apparently allopatric
lowland Myrmeciza species with
broadly similar calls. As a disclaimer,
the paper is still being finalised, there are strong bare-skin as well as
plumage differences and they are in a different section of the paraphyletic Myrmeciza tree. But this would otherwise seem a very analogous
situation to M. nigricauda / palliata in
a more closely related group than Hypocnemis
and one that will give support to Chaves et al.’ proposals in light of the
Isler study.
“I would thank the authors and others for
considering my concerns in such a detailed, sensible and collegiate manner, and
would now support this proposal, if not entirely for the reasons set out in the
Chaves et al., paper, then for the reasons set out in this discussion. The authors and Islers should also be
encouraged to produce a short note for Condor
making a few corrections and discussing some of the additional points in
this exchange of communications. This
proposal may have taken up a lot of space on the SACC website, but hopefully it
makes for interesting reading and everyone involved in this discussion now
seems to be in agreement.
“[Thanks to Danny Zurc (Museo de Ciencias
Naturales de La Salle, un proyecto cultural del Instituto Tecnologico
Metropolitano) for the photograph of the CSJ specimens; and Alonso Quevedo and
Trevor Ellery for information on birds at Las Tangaras.]”
Comments from Stiles: “YES, especially given the additional
information provided by the Islers that resolved Donegan’s (reasonable) doubts
regarding vocalizations. Perhaps
unfortunate that Chaves et al. did not discuss plumage characters, because
males of palliata and nigricauda differ strongly, females more
subtly but consistently, adding another set of characters favoring species
status.”
Comments from Pacheco: “YES. Após é a análise adicional dos Islers, a partir das
construtivas colocações de Donegan.”
Comments
from Robbins:
“YES. The process that has
occurred during the evaluation of this proposal is precisely how we want the
Committee to function. All parties should be congratulated not only in the new
insights that were brought to bear on this perplexing problem, but also in the
manner in which it was presented.”
Comments from Nores: “YES. Song differences (Xeno-canto) are noticeable. Moreover, the molecular analysis by Chavez et al. (2010) clearly shows a highly supported clade for the laemosticta complex with the four taxa forming a polytomy.”
Comments from Pérez-Emán: “YES. As indicated by Mark, the evaluation of
this proposal is a clear example of a constructive peer-reviewed process
leading to a stronger documentation of the evidence supporting species status
in this group. As Donegan pointed out, a short note including some of the
issues raised here and providing the new evidence seems to be warranted.”