Proposal (964) to South
American Classification Committee
Note from Remsen: This is a proposal submitted to and rejected
unanimously by NACC. Although the
comments are not yet public, all voters agreed with the synopsis in the
proposal, i.e. almost certainly more than one species is involved, data are
insufficient for resolving the boundaries in this complex group.
Treat Xiphorhynchus aequatorialis
as a separate species from Spotted Woodcreeper X. erythropygius
Description of the problem:
Xiphorhynchus erythropygius is an uncommon
species of upper tropical and lower montane zones from central Mexico (San Luis
Potosí) south through Central America and the Chocoan forests as far south as
southern Ecuador (Marantz et al. 2020). Although its distribution is largely
contiguous, there are multiple breaks in lowland zones. One of these is in
Nicaragua and divides the species into a northern (erythropygius) group and southern (aequatorialis) group, with the species absent from most of the
southern half of Nicaragua (Vallely and Dyer 2018, Marantz et al. 2020). The
northern group is composed of erythropygius
("Sclater, PL", 1860) from north of the Isthmus of Tehuantepec
and parvus Griscom, 1937 to the south
of the isthmus. The southern group is composed of punctigula (Ridgway, 1889) from Nicaragua to central Panama, insolitus Ridgway, 1909, from central
Panama to central Colombia (including the Magdalena Valley), and aequatorialis (von Berlepsch &
Taczanowski, 1884) from central Colombia to southwestern Ecuador. Olive-backed
Woodcreeper (Xiphorhynchus triangularis) of the Andes is part of
this complex, and some authors have considered all taxa to be part of triangularis (see below). Hilty and
Brown (1986) noted that triangularis
is an upper elevation (above 1,500 meters) replacement of aequatorialis on the west slope of the Andes in Colombia.
Taxonomic history:
Ridgway (1911) considered erythropygius monotypic but noted that Berlepsch and Stolzmann
(1896) considered erythropygius to be
a subspecies of triangularis. Ridgway
(1911) split punctigula (with insolitus as a subspecies) as
Spotted-throated Woodhewer, with the following comment: “Somewhat like X. erythropygius,
but color of pileum, back, and under parts greenish or ocherous olive instead
of olive-brown, back without streaks or with very narrow ones on anterior
portion only, and throat spotted rather than barred with dusky.” He gave the
range of punctigula/insolitus as Nicaragua (San Rafael del
Norte) to northwestern Colombia (Río Truando). Berlepsch & Taczanowski
(1884) described aequatorialis as a
subspecies of erythropygius, but aequatorialis was overlooked by Ridgway
(1911) who considered punctigula as
the name for the southern group, although aequatorialis
has priority.
Cory and Hellmayr (1925), perhaps following
Berlepsch and Stolzmann (1896), considered all taxa in the complex to be part
of X. triangularis, with the
following English names for the relevant taxa: Pacific Wood-Hewer for aequatorialis, Truando Wood-Hewer for insolitus (presumably based on the Río
Truando in northern Colombia), Spotted-throated Wood-Hewer for punctigula, and Spotted Wood-Hewer for erythropygius. Cory and Hellmayr’s
comments on the reasoning for lumping all these taxa are worth reproducing here
in full, as they constitute (as far as we can tell) the most comprehensive
comments on plumage variation in the complex, with taxa arranged from
south-to-north:
“Xiphorhynchus triangularis aequatorialis (Berlepsch and
Taczanowski): Differs from X. t.
triangularis in more brownish (less olivaceous) upper parts; plain
(unspotted) crown, with only a few narrow buff streaks on forehead; the much
deeper chestnut rufous of wings and tail spreading also over the lower back;
much deeper buff throat, with the olive markings restricted to small, rounded
apical spots; larger spots on breast and abdomen; uniform horn brown maxilla,
etc.
“Xiphorhynchus triangularis insolitus
appears to have been based on intergrades between aequatorialis and punctigula.
The specimen listed above, obtained by A. Schott on Lt. N. Michler's Expedition
to the lower Atrato [northwestern Colombia], has the back decidedly browner
than the majority in the series of the two forms, though it is very nearly
matched by a female from Bulun, Prov. Esmeraldas, Ecuador, and an unsexed
individual from Chiriqui [Panama]. Markings of throat and spotting on
underparts are exactly as in punctigula.
On the other hand, two skins from Calovevora, Veragua [Panama] hence not far
from the type locality of insolitus
and in the same general region I am quite unable to distinguish from Costa
Rican specimens of punctigula, which,
moreover, is sometimes hard to separate from aequatorialis. Individual variation in these birds is much greater
than generally admitted.
[Regarding a
specimen from San Rafael del Norte in northern Nicaragua] In the amount of
spotting above, this bird is exactly intermediate between punctigula and erythropygia,
but resembles the former in olivaceous coloration and restricted rufous
uropygial area.
“Xiphorhynchus triangularis punctigula. Birds
from Veragua (Calovevora) and Chiriqui [Panama] are identical with those from
Costa Rica. X. t. punctigula is
exceedingly close to X. t. aequatorialis,
but generally distinguishable by brighter olivaceous under parts with smaller
buff spots, more heavily spotted throat, somewhat lighter rufous rump and
wings, etc. Single specimens are, however, not always separable. Through
individual variation, it also intergrades with X. t. erythropygius, of Guatemala. There is notably a specimen from
Chiriqui (at Tring), which combines the greenish olive coloration of punctigula with the heavy spotting, both
above and below, of erythropygia.
Similar examples are no doubt responsible for Panama records of the last named
race.”
In a departure from his typical pattern of
lumping taxa without comment, Peters (1951) split the Choco/Middle American
taxa from X. triangularis (although again without comment), a treatment
maintained by Eisenmann (1955), Wetmore (1972), AOU (1983), and most current
authors.
Multiple authors (e.g., Eisenmann 1955, AOU
1983) noted that the aequatorialis
group is sometimes recognized as a separate species from erythropygius, a treatment formalized by HBW-BirdLife: "[aequatorialis] Hitherto considered
conspecific with X. erythropygius,
but differs in its much less obvious, less teardrop-shaped (and often minimal)
pale streaking on mantle and back (2); darker chestnut tail (1); slightly less
dense pale spotting on underparts (1); higher maximum frequency of whistles in
song after first whistle (2), and overslurred vs downslurred whistles in song
after first whistle (2) (Boesman 2016)."
AOU (1983) account: populations from eastern
Nicaragua southward, occurring commonly in lowland habitats, are sometimes
recognized as a species, X. aequatorialis
(Berlepsch and Taczanowski, 1884) [SPOT-THROATED WOODCREEPER], distinct from X. erythropygius. The widespread South
American species, X. triangularis
(Lafresnaye, 1842), and X. erythropygius
are regarded as conspecific by some authors; they constitute a superspecies.
New information:
Although many studies have sampled Xiphorhynchus erythropygius for
phylogenetic work, most included only a single sample, so are not of use here.
The sole study we have been able to find that included multiple taxa is Weir
(2009), who sampled three individuals and sequenced the mitochondrial locus
cytochrome-b. Samples from El Copé, Panama, and Darién, Panama (both insolitus under current taxonomy), were
sisters, whereas one from the western slope of the Andes (=aequatorialis) was sister to those two. However, no genetic
distances were reported, and the northern erythropygius
group was not sampled. Two samples in Harvey et al. (2020) were both of erythropygius (sensu stricto), whereas two samples in Aleixo (2002) were both of aequatorialis. Multiple studies found erythropygius/aequatorialis as sister to
X. triangularis.
Below are photos of most taxa in the group, from
the collections at the Louisiana State University Museum of Natural Science
(LSUMNS). The two samples of insolitus
are from Darién, Panama, so east of the canal zone.
The specimens at LSUMNS show a confusing
patchwork of plumage variation that do not readily align with current species
limits. The one taxon in the complex not represented in the LSUMNS collections
is the Venezuelan X. t. hylodromus
(see photo in Macaulay Library: https://macaulaylibrary.org/asset/205397931).
The plumage character that most readily
distinguishes X. triangularis from X. erythropygius (as currently defined)
is the scalloped vs spotted throat. However, nominate triangularis (with hylodromus
based on the Macaulay photo above) shares the extensive and broad streaking on
the belly shown by all taxa in X.
erythropygius, and is quite distinct in this regard from the two southern
taxa in X. triangularis (intermedius and bangsi), which show sparse streaks on the belly. Within X. erythropygius, the two northern taxa
(Spotted group) show extensive dorsal
streaking not shown by other taxa, whereas the three southern taxa (Berlepsch’s group) show less crown spotting than
either the Spotted group or X. triangularis, although one specimen
of aequatorialis seems to show some
crown spotting (Figure 1, right hand specimen).
Vocal variation
To our knowledge the only quantitative analysis
of vocal variation within the X.
erythropygius / X. triangularis complex
comes from Boesman (2016), who described vocal variation within X. erythropygius. There is considerable
variation among recognized subspecies across the two currently recognized
species. We are not aware of any rigorous playback studies on this group.
Between the currently recognized subspecies
within X. erythropygius, there are
some slight differences across the putative split in question, but they are
overall quite similar. Both groups
Figure 1: Dorsal view of LSUMNS specimens of X. erythropygius and X. triangularis.
Figure 2: Ventral view of LSUMNS specimens of X. erythropygius and X. triangularis.
Figure 3: Lateral view of LSUMNS specimens of X. erythropygius and X. triangularis.
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emit a similar series of 2-4 whistles each of
approximately 0.5–1.0 s in length. However, the erythropygius / parvus group
has little to no frequency modulation in these whistles and is slightly lower
in pitch, starting at ~2.5 kHz and descending to ~1.5 kHz. Among the
Berlepsch’s group of punctigula / insolitus / aequatorialis, the nearest
neighbor X. e. punctigula in Costa
Rica has a similar structure in the series of whistles to the erythropygius / parvus group, but the first punctigula
note has considerably more frequency modulation and higher pitch overall,
starting at ~3.5 kHz and descending to ~2.5 kHz. The songs of X. e. aequatorialis are the most
distinct among these in having much more frequency modulation in each of the
notes, giving them much more of a ‘quavering’ tone compared to the pure
‘whistled’ tone of those in Costa Rica or north of Nicaragua. The quavering
tone seems to extend to the west of the Canal Zone in Panama, but then becomes
decidedly more clear east of the Canal Zone. The type locality of insolitus is in Coclé, Panama, so insolitus would be of the northern vocal
type. Please note that these observations are qualitative and may not stand up
to a more rigorous quantitative analysis of larger sample sizes for vocal
variation within the group.
Boesman (2016) divided X. erythropygius into two vocal groups, a northern one (comprised
of erythropygius and parvus) and a southern one (comprised of
punctigula, insolitus, and aequatorialis),
and his results largely agree with what we describe above. Additionally, he
described the erythropygius group as
having downslurred notes, whereas the aequatorialis
group has overslurred notes. This difference is quite subtle to our ears, and
the strong frequency modulation of aequatorialis
(not present in punctigula and insolitus) and lower pitch of the erythropygius group seem like more
distinct characters. Boesman (2016) stated that the quavering songs change
gradually from north to south, but it seems to us that there may be a clear
break between pure-toned and quavering songs near the canal zone of Panama.
However, some examples even from the northern group seem to have a quavering
tone to some songs.
Macaulay Library holdings for erythropygius / parvus songs from N of Nicaragua:
https://search.macaulaylibrary.org/catalog?taxonCode=spowoo2&mediaType=audio&view=list
https://search.macaulaylibrary.org/catalog?taxonCode=spowoo1&mediaType=audio®ionCode=MX
Macaulay Library holdings for punctigula / insolitus / aequatorialis song from S of Nicaragua:
https://search.macaulaylibrary.org/catalog?taxonCode=spowoo3&mediaType=audio&tag=song&view=list
An example of the quavering song immediately
east of the canal zone in Panama: https://xeno-canto.org/253672
But songs of birds immediately west of the canal
zone in Panama are whistled like those from Costa Rica:
However, some recordings of parvus are somewhat quavering, but otherwise match typical parvus songs in pattern and lower pitch:
https://macaulaylibrary.org/asset/527388
Because X.
triangularis has been considered part of the same species, we have here
provided some recordings from the nearest populations in Colombia. However,
there are not many recordings of the song of this species, and recordings from
farther south in the Andes sound quite different from those in the north. The
short descending whinny of these northern birds is quite different from the
songs of any of the taxa currently considered part of X. erythropygius.
Schulenberg et al. (2007) described the song of
the northern Peruvian populations of X.
triangularis as a “mellow, decelerating, descending series of musical
whistled notes: “whi’we-we-we-we we we
wur”, which agrees with the recordings linked to above, but they noted that
the southern Peruvian (Pasco south) X. t.
bangsi has an additional song, a wiry insistent rising-falling series of
nasal whines: “WHEEEW
who-WHI-WHI-whi-whi-whi” suggesting some vocal variation within X. triangularis. An example of that
latter song is here: https://xeno-canto.org/746087 All song recordings available online from south of the Marañón Valley
seem to match this latter nasal song type.
Very few examples of hylodromus are available online, all in Macaulay, and it is not
clear if these refer to natural songs:
https://media.ebird.org/catalog?taxonCode=olbwoo1&mediaType=audio®ionCode=VE
Effect on AOS-CLC area:
Splitting X.
aequatorialis from X. erythropygius would
result in one additional species for the AOS area. Splitting X. aequatorialis and X. punctigula from X. erythropygius would result in two additional species for the AOS
area.
Recommendation:
We recommend a NO on any splits in this group at this time.
Although we suspect that multiple species may be
involved within what is currently treated as X. erythropygius, it is not clear where best to split taxa as the
different data types are not concordant in their clustering. Vocal data suggest
three song groups within X. erythropygius,
a low-pitched group with clear whistles (erythropygius
/ parvus), a higher-pitched group
with clear whistles (punctigula / insolitus west of the canal zone) and a
quavering song group (aequatorialis
east of the canal zone). The vocal aspect of the BirdLife split is based on
song pitch and downslurred vs overslurred notes but minimized the
diagnosability of the distinctive quavering songs of aequatorialis. However, quantitative analyses are likely necessary
to ascertain whether there is a gradual change in clear-noted to quavering
songs as suggested by Boesman (2016). The differences between the songs of
these groups do not seem as drastic as the differences between X. erythropygius and X. triangularis, and the songs of the
southern X. triangularis (bangsi) seem more distinct than do the
three groups within X. erythropygius.
Plumage data support the distinctiveness of the erythropygius / parvus group based on their extensive mantle and crown streaking.
However, the two southern groups (punctigula
and aequatorialis) show ventral
streaking similar to the northern taxa in X.
triangularis, although they differ from X.
triangularis in throat pattern. We are unable to find consistent plumage
differences between punctigula/insolitus and aequatorialis (which agrees with comments by Cory and Hellmayr
1925, see above) despite apparent differences in song.
This complex is an excellent candidate for
future work. Quantitative analysis of song, plumage, and genetic variation (the
latter of which is lacking) would go a long way towards resolving species
limits in the group.
If any of these splits gain traction, an English
name proposal should be drafted to address the new names. Cory and Hellmayr
(1925) provided some options to work with, which adapted for modern conventions
would be:
• Spot-throated
Woodcreeper for punctigula (which
would include insolitus).
• Spotted Woodcreeper for erythropygius
(although this has now been used for X.
erythropygius s.l., so a new name may be necessary)
• Pacific
Woodcreeper for aequatorialis s.s.
AOU (1983, 1998) used Spot-throated Woodcreeper
for the aequatorialis group (when
separated from X. erythropygius,
although we note that both groups have spotted throats). Clements/eBird gives
Berlepsch’s Woodcreeper as the English name for this group.
Please vote on the following:
1)
Elevate aequatorialis
(with punctigula and insolitus) to species rank (BirdLife
treatment)
2)
Elevate both punctigula
(with insolitus) and aequatorialis to species rank
Literature Cited:
Aleixo, A. 2002. Molecular systematics and the role of the
“várzea”–“terra-firme” ecotone in the diversification of Xiphorhynchus woodcreepers (Aves: Dendrocolaptidae). The Auk
119(3): 621-640. https://doi.org/10.1093/auk/119.3.621
AOU. 1983. Check-list of North American Birds. The species of birds of
North America from the Arctic through Panama, including the West Indies and
Hawaiian islands. 6th edition. American Ornithologists’ Union.
AOU. 1998. Check-list of North American Birds. The species of birds of
North America from the Arctic through Panama, including the West Indies and
Hawaiian islands. 7th edition. American Ornithologists’ Union.
Berlepsch, G. H. von, and L. Taczanowski. 1884. Liste des Oiseaux
recueillis par MM. Stolzmann et Siemiradski dans l’Ecuadeur occidental.
Proceedings of the Zoological Society of London 536-577.
Berlepsch, G. H. von, and J. Stolzmann. 1896. On the ornithological
researches of M. Jean Kalinowski in central Peru. Proceedings of the Zoological
Society of London 322-388.
Boesman, P. 2016. Notes on the vocalizations of Spotted Woodcreeper (Xiphorhynchus erythropygius). HBW Alive
Ornithological Note 82. In: Handbook of the Birds of the World Alive. Lynx
Edicions, Barcelona. (retrieved from http://www.hbw.com/node/931976).
Cory, C. B. and Hellmayr, C. E. 1925. Catalogue of birds of the
Americas, part IV. Field Museum of Natural History Zoological Series Vol. XIII.
Chicago, USA.
Eisenmann, E. 1955. The species of Middle American birds. Transactions
of the Linnaean Society of New York. Vol. VII.
Harvey, M.G., A. Aleixo, C.C. Ribas, and R.T. Brumfield. 2017. Habitat
association predicts genetic diversity and population divergence in Amazonian
birds. American Naturalist 190: 631-648.
Hilty, S. L., and W. L. Brown. 1986. A Guide to the Birds of Colombia.
Princeton University Press.
Marantz, C. A., J. del Hoyo, N. Collar, A. Aleixo, L. R. Bevier, G. M.
Kirwan, and M. A. Patten. 2020. Spotted Woodcreeper (Xiphorhynchus erythropygius), version 1.0. In Birds of the World
(S. M. Billerman, B. K. Keeney, P. G. Rodewald, and T. S. Schulenberg,
Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.
https://doi.org/10.2173/bow.spowoo1.01
Peters, J. L. 1951. Check-list of birds of the world. Vol. VII. Museum
of Comparative Zoology at Harvard College.
Ridgway, R. 1911. The birds of North and Middle America. Part V.
Bulletin of the United States National Museum. No. 50.
Schulenberg, T. S., D. F. Stotz, D. F. Lane, J. P. O’Neill, and T. A.
Parker III. 2007. Birds of Peru, revised and updated edition. Princeton
University Press.
Vallely, A. C. and D. Dyer. 2018. Birds of Central America. Princeton
University Press.
Weir, J. 2009. Implications of genetic differentiation in Neotropical
montane forest birds. Annals of the Missouri Botanical Garden 96(3): 410-433. https://doi.org/10.3417/2008011
Wetmore, A. 1972. The Birds of the Republic of Panamá. Part
3.-Passeriformes: Dendrocolaptidae (Woodcreepers) to Oxyruncidae (Sharpbills).
Smithsonian miscellaneous collections, v. 150.
Oscar Johnson and Nicholas A. Mason, February
2023
Note
from Remsen on voting: Although I didn’t put this in the proposal title, note
that there are two parts, which require separate votes:
964.1.
Elevate aequatorialis (with punctigula and insolitus) to species rank (BLI treatment)
964.2. Elevate both punctigula (with insolitus)
and aequatorialis to species rank
Note
from Remsen on English names: if this passes, a separate proposal would be
needed; see discussion of possibilities above.
Comments
from Remsen:
“I’m not voting on this one – I have asked Jorge to take my slot. What I said on the NACC version was ‘No for all the reasons given
in the proposal (which is outstanding).
As noted in the proposal, this is a complex situation that requires a
rigorous, formal, published study to change species limits, and it seems clear
that changes are needed, even from the largely anecdotal information presented
so far.’
Comments from Areta: “NO, following the rationale in the
excellent proposal. After hearing to several vocalizations, I could not find
any clearly diagnostic feature of each taxon. There seems to be a lot of
geographic variation, and some vocalizations sound quite intermediate. Until
someone performs a more rigorous vocal study, I prefer to keep these as one
species. Xiphorhynchus triangularis
is also in need of a taxonomic review, of course.”
Comments
solicited from Curtis Marantz (voting for Pacheco): “NO. I am in agreement with the
recommendation to recognize no splits at this time. I should begin by noting that this is a
mostly highland complex for which I have very little field experience, and as
such, I am not in as good a position as I am with the lowland taxa to comment
on the variation that I see or hear in the photos and recordings, or in past
treatments of the group. It has also been a very long time now since I last
looked at any of this, because even though they have contacted me regarding
some of the HBW accounts, this was not one of them, so I have had no input
whatsoever on anything in the newer HBW account beyond what I wrote back in 2001,
and to be honest, I cannot even recall now if I wrote the taxonomic section for
this entry (though I think I did write this one).
“This said, the plumage variation is rather complex and
confusing. Moreover, I am not sure how
important things like the extent of spotting or the tone of olive or brown in
the plumage is for species-level differences.
These seem more like subspecies-level differences to me. I feel better about discrete differences,
such as those shown between the Central American and Amazonian populations of
the Barred Woodcreepers, and especially so when they correspond to very
striking vocal differences. I suppose
the first thing one would want is a detailed analysis based on many specimens
of each taxon to see how consistent these plumage differences really are.
“With regard to the vocal differences, my recommendation would be
that a much larger sample is required, not only to examine individual and
regional variation in the song of the species, but also to examine the
repertoire more carefully to ensure that you are not comparing songs with
calls. Even within the sets of recordings from smaller areas, I am hearing
sufficient variation to conclude that both songs and calls are included in
these samples, but I do not know these birds sufficiently well to determine
which sounds are homologous. In the Xiphorhynchus guttatus complex,
which I know best, there are several different calls and extensive variation in
the songs, some if it motivational and not regional. From listening to the
various recordings linked, it becomes immediately apparent that the recordings
from the Macaulay Library show a break between the clear and quavering songs to
be well south of where the species-groups are divided, with recordings from
Costa Rica and those from Ecuador having rather different songs despite both
being treated under the category Spotted Woodcreeper (Berlepsch's). I also found some recordings in which the
initial element was quavered but the others were clear, which may suggest to me
that there is a motivational aspect to the quavered elements.
“So, in the end, I do agree that there are interesting patterns
evident, and possibly even more than one species involved, but as with many
such cases in woodcreepers, I feel that it is premature, given the information
available, to make any taxonomic decisions. Then again, I am also one who tends
to be of the opinion that taxonomy should remain as stable as possible unless
there is a really compelling reason to make a change. If not, the result is
that others will conclude that the bodies making these decisions do not really
have a solid grasp on what they are doing and are just trying to jump on the
newest suggestions based on incomplete data.”
Comments
from Robbins:
“I vote NO for elevating any of the taxa currently in
Xiphorhynchus erythropygius to species level for the reasons that
Oscar and Nick have detailed in their thorough proposal. It appears that there
is considerable variability in all character states mentioned and genetic data
are lacking across the entire complex. Yes, likely more than one species
involved in the complex, but clarifying what taxonomic changes need to be made
will require much more data.”
Comments from Lane: “NO. As a believer in the concept of subspecies, I see the
variation demonstrated within X. erythropygius here as in line with my
expectations of furnariid subspecific variation.
As an aside, I would point out
that the proposal made the comment that within X. triangularis "All song recordings available online
from south of the Marañón Valley seem to match this latter nasal song type."
This is not true, as illustrated by https://macaulaylibrary.org/asset/531434and https://macaulaylibrary.org/asset/534618. The
wiry song described in Schulenberg et al. seems to be genuinely limited to more
southerly Peruvian and Bolivian populations; central Peru seems poorly sampled
for voice of this species. Nevertheless, the well-sampled San Martín area
population lacks this wiry song, seeming more aligned with the north of the
Marañon voice type. This taxonomic issue is best saved for some future
proposal, however.”
Comments
from Stiles:
“NO, on current evidence in which genetics, plumages and perhaps vocalizations
appear not to concur.”
Comments
from Jorge Pérez-Emán (voting for Remsen): “This proposal aims to treat the
subspecies Xiphorhynchus erythropygius
aequatorialis as a separate species (aequatorialis)
from X. erythropygius. It also
elaborates on the potential for an additional species (punctigula), the relationship of these taxa with X. triangularis, and the geographical
differentiation of triangularis (just
briefly). The evidence put into the proposal is thorough and provide a good
picture of geographical variation both in plumage patterns and vocalizations.
Based on such information, it is clear we don´t have enough data to understand
species limits in this complex, so my short answer will be NO and NO to both
parts of the proposal (two or three species, when considering punctigula also as a different species).
I elaborate a bit more below, and provide additional complementary information
on molecular data, thanks to Brant Faircloth who extracted mitochondrial
sequences from UCEs data from the suboscines project (from Harvey et al. 2020)
to provide molecular data of the northern erythropygius
group.
“1.
Differences in plumage coloration and size are minor among recognized
subspecies. However, on top of that and as clearly indicated in the proposal,
the large amount of individual variation shown by X. erythropygius specimens compromise any pattern of geographical
variation previously used to define taxon limits. Such awareness for individual
variation is not new and was emphasized by previous researchers (Cory and
Hellmayr 1925, Griscom 1937), some even indicating the potential effects of
foxing in museum specimens and age in such variation (Wetmore 1972, Griscom
1937). Even with a short series, pictures of LSUMNS specimens taken by Oscar
and Nick reveal plumage differences between two specimens of aequatorialis (differences that suggest
even potential diagnostic patterns are variable). Additionally, Cory and
Hellmayr (1925, and also Griscom 1937) highlighted different aspects of this
variation suggesting the presence of intermediates between punctigula and parvus
(specimens from San Rafael del Norte, Nicaragua, and Chiriqui, Panama). In
fact, I am not quite sure when the San Rafael del Norte specimen was
transferred to punctigula, but
Griscom (1937) already included there. The same pattern was highlighted by
these authors (as noticed in the proposal) for aequatorialis and insolitus
in Colombia, where limits of distribution are unclear and some localities were
considered as dubious (about what taxon was present) by M. de Schauensee (1950,
lower Cauca Valley, La Frijolera).
“2.
Variation in vocalizations seems to better differentiate some groups but is not
clear cut. Analyses from Boesman (2016) and this proposal found a major break
between the northern and southern group (erythropygius/parvus vs. punctigula/insolitus/aequatorialis, respectively), though
diagnostic vocal characters differed between both analyses. However, the most
different vocalization corresponded to aequatorialis
compared to other taxa and there is individual variation that makes difficult
to understand differences between punctigula
and insolitus or even between these
taxa and the northern group taxa (as highlighted in this proposal). A pattern
of variation worth mentioning is the suggested break of vocalization
similarities at the Canal zone, with birds east of it similar to aequatorialis and birds west of it more
similar to punctigula and the
northern group. This pattern suggests insolitus
vocalizations group with different taxa depending on location relative to the
Canal zone. With much variation and no certainty about the cause of these
differences (as pointed out by Curtis), deciding how to group these taxa is
difficult. The proposal also makes clear that patterns presented are
qualitative and require formal analysis with larger data. Unfortunately,
Boesman (2016) does not indicate sample size for his analysis, making difficult
to evaluate how consistent are the reported differences.
“3.
I gathered all available molecular information (both from GenBank and Brant
Faircloth) to complement this proposal with some hints on genetic variation,
doing a quick phylogenetic analysis and some molecular pairwise comparisons.
Previous phylogenetic information showed triangularis
to be the sister taxon of erythropygius
(Derryberry et al. 2011; Harvey et al. 2020), a relationship that holds
here with increasing taxon representation for each species (Figure 1).
Figure 1. Maximum Likelihood hypothesis of
phylogenetic relationships of Xiphorhynchus
erythropygius species complex. In the left figure is the hypothesis based
on both ND2 and cytochrome b genes, while the right figure shows only the
relationships within X. erythropygius
based on just cytochrome b gene. Color boxes highlight relationships within
(and between) both X. erythropygius
and X. triangularis. Sequences
obtained either from GenBank (identified by their code starting with AY, GU or
FJ) or from the UCEs data of the suboscine phylogeny (Harvey et al. 2020, mitochondrial genes
courtesy of Brant Faircloth). Numbers at nodes represent bootstrap data
obtained from 1000 pseudoreplicates of the fast algorithm of RAxML. Localities: HI_MX = Hidalgo, Mexico; LI_CR = Limón, Costa Rica; CH_PA =
Chiriquí, Panama; BT_PA = Bocas del Toro, Panama; CO_PA = Coclé, Panama; PA_PA
= Panama, Panama; DA_PA = Darién, Panama; SPt_TT = Saint Patrick, Trinidad and
Tobago; ES_EC = Esmeraldas, Ecuador; PI_EC = Pichincha, Ecuador; EO_EC = El
Oro, Ecuador; CA_PE = Cajamarca, Perú; LO_PE = Loreto, Perú; PA_PE = Pasco,
Perú; LP_BO = La Paz, Bolivia; SC_BO = Santa Cruz, Bolivia.
“Molecular
data allow for a complementary view of geographical variation from a different
character set. An important add-on to previous analyses is the availability of
one sample of erythropygius from
Hidalgo, Mexico (erythropygius).
Haplotypes from this specimen are sister to the rest of haplotypes (punctigula, insolitus, aequatorialis;
parvus not included) with large
genetic divergence between them (around 5% in ND2, and 4% in Cytb). Such
genetic divergence and sister relationship is in agreement with suggestions
that this taxon is a candidate for a separate species (or aequatorialis, including the southern group, being a separate
species). Variation within the aequatorialis
group is somehow complex. The most complete available molecular data is for the
cytochrome b gene, and it shows a non-monophyletic aequatorialis with high support and some structure suggesting
western Panama and Costa Rican taxa conforming a group that separates from
another one that includes both east and west Canal zone populations (Darien and
Coclé, Figure 1). Whether the Coclé specimen is insolitus is unclear as it comes from the Pacific slope of Coclé
(El Copé National Park), perhaps less than 30km to one of the closest
localities associated to punctigula (Chitra,
Panama; Wetmore 1972). These sequences are very similar (about 0.3% divergent)
and differed a bit when compared to western Panama/Costa Rica sequences (about
0.6%), but still very similar. Sequences from aequatorialis diverge in average 1.4% from these punctigula/insolitus but are more similar to the Darien one (1.2%) than the
ones from the west Canal zone (1.6%; including the Coclé sequence). However,
these are very similar numbers which might not mean much based on the small
sample size.
“4.
Even when we could be tempted to make some conclusions from the plumage,
vocalizations and molecular patterns at hand, geographical differentiation and
species/taxon limits are difficult to understand as geographical sampling is
far from being representative and different characters vary differently with
geography as pointed in the proposal. There are unclear geographical breaks
based on plumage variation (with some intermediates found throughout Central
America and northern Colombia, based on the literature) and vocal data suggest
a complex differentiation in Panama (breaking potential insolitus in two potential groups, west and east of the Canal zone)
with the largest variation associated to aequatorialis.
Molecular data show a large differentiation of erythropygius compared to the southern group, which does not
differentiate much genetically. However, data from specimens collected west and
east of the Canal zone (Darien and Coclé) group together, contrasting with
vocalization data. It is worth to highlight the fact that the area from Colón
to Veraguas (east and west Canal zone) have been identified as a potential
suture zone in which morphology and molecular data are not congruent between
each other (McLaughlin et al. 2020 Cotinga 42:77-81; McLaughlin et al. 2023,
bioRxiv). This could explain the lack of correlation among all sets of
characters in this area and make it hard to understand, with current data, the
relationships between punctigula, insolitus and even aequatorialis. If we add the lack of data for the region of
potential contact between insolitus
and aequatorialis or punctigula and parvus (and between the northern group subspecies), we realize we
are far from reaching a conclusion regarding species/taxon limits in this
complex.
“5.
To expand on the discussion of X.
triangularis, plumage variation seems to be larger between triangularis (and hylodromus) and intermedius/bangsi. In the proposal, Oscar and Nick
did not have access to skins of hylodromus.
I am including two pictures (taken by Miguel Lentino from Colección Ornitológica
Phelps) in which you can see the large similarity between both taxa. Wetmore
(1939, Smith. Misc. Coll. 98) described hylodromus
as “brighter olive brown above; expose
surfaces of secondaries darker, less reddish brown; under surface lighter, more
greenish olive, more abundantly spotted, the spot lighter colored; throat
decidedly lighter, with the dark marginal lines on the feathers reduced in
width (underlining mine).” Many of these differences are really tenuous
and with a series such as the one in the picture (Figure 2), showing large
individual variation throughout the distribution of the species in Venezuela, a
reevaluation of geographical differentiation is needed to recognize (or not)
the presence of two subspecies. The major difference is on the throat, lighter
in hylodromus, part of the effect
given by the reduction of dark marginal lines on the feathers (Figure 2, right
picture). Regarding distribution of these taxa in Venezuela, and perhaps a
consequence of the tenuous differences between them, Hilty (2003) indicated hylodromus has a distribution along the
northern Cordillera of Venezuela extending to the northeastern Andean
Cordillera (Lara and Trujillo). However, these specimens were suggested to be
either intermediate in plumage coloration between both taxa (Phelps and Phelps,
ms.) or should be better placed in triangularis
(M. Lentino, pers. comm.). Unfortunately, Hilty (2003) did not provide any
criteria to understand how he assigned localities to these taxa.
Figure
2. Pictures of Xiphorhynchus triangularis
triangularis and X. t. hylodromus
from Venezuela (pictures taken by Miguel Lentino from Colección Ornitológica
Phelps). On the left, ventral view of a short series of specimens showing the
large similarity between these taxa. The major difference between them is the
lighter throat in hylodromus shown in
the right picture.
“Molecular
data and phylogenetic analyses (Figure 1) also suggest a major break
potentially associated to the Huancabamba Dry Valley or Marañon river.
Sequences were available from Cajamarca, Peru and Zamora-Chinchipe, Ecuador
(not shown in the figure), north of Marañon river (both triangularis, diverging by just 0.2%), and, south of the Marañon,
from Pasco, Peru (intermedius) and La
Paz, Bolivia (bangsi), also very
similar genetically (0.3-0.4%). These data show that there might be a large
break between triangularis and both intermedius/bangsi but the geographical range of triangularis is largely unsampled. On the other hand, sequences of intermedius and bangsi are very similar (suggesting either current gene flow or
recent divergence) compared to vocalizations that appear to be largely
different (based on southern records (potentially bangsi) of Tom Schulenberg. However, the geographical distribution
of these vocal differences and the real nature of it (i.e., larger vocal
diversity, frequency of each vocalization in the repertoire) is unclear as Dan
Lane recordings from San Martin, Peru, suggest a similar vocalization of this
population (intermedius) to triangularis and we don´t know where, if
any, is the break between these type of vocalizations.
“In
summary, the proposal clearly indicates that even when phenotypic
differentiation of X. erythropygius
suggest more than one species within this group, the complexities of this
variation, the lack of correlation among characters, and the lack of formal
analyses, sample sizes and geographical representation, do not allow to make
any definitive conclusions at this point. The same goes for X. triangularis, included in the
proposal as historically considered to form a species or species complex with X. erythropygius.”
Comments
from Zimmer:
“NO. As laid out nicely in this proposal, we simply don’t have enough
information in my opinion to make sense out of the observed variation. Sample sizes and geographic breadth of
genetic data seems insufficient to do much with, and plumage variation, while
notable at the extremes, seems to not be concordant with currently recognized
taxa, and intra-taxon variation looks, in some cases, to exceed or equal
between-taxon variation. Vocal
distinctions are much more impressive to me, as I would expect to be the case
with tree-hugging, forest-interior inhabiting, suboscines of a group in which
plumage seems to be evolutionarily conservative, and in which minor
distinctions are unlikely to be used by the birds themselves for sorting one
another out. As Curtis pointed out in
his comments, it is especially important that any quantitative vocal analysis
compares homologous vocalizations from one taxon to the next, and in the linked
audio recordings, I’m seeing some instances where the vocalizations being
compared are not clearly homologs. This
was particularly the case with the referenced recordings of X. triangularis
hylodromus from Venezuela, all of which I would label as calls and not
songs. It has been some years since my
last field exposure to members of the erythropygius-triangularis
complex, but my recollection is that the two currently recognized species
(Spotted and Olive-backed) always struck me as vocally distinct (at least in
their songs), and that vocal differences from one place to another in Spotted
Woodcreepers were a matter of degree, not of kind. I also remember individual Spotted
Woodcreepers giving altered songs in response to playback, and those
alterations involved differences in number of notes, pace, and degree of
frequency modulation, the latter altering the quality of the vocal elements –
something I’m certain would have been visible in spectrograms. It is my experience that woodcreepers, in
general, tend to give all kinds of twisted, qualitatively different
vocalizations in response to playback (as is also the case with the various Sclerurus
species of Leaftossers), and therefore, any attempts at quantitative vocal
analyses need to be of spontaneously vocalizing birds and homologous
vocalizations. All of that being said, I
will say that my personal experience with Spotted Woodcreepers is mostly from
Mexico to c Panama (west of the Canal Zone), and it is those birds whose voices
I would describe as differing in only subtle ways from one another. I was struck by how consistently different
all of the songs of aequatorialis that I listened to from the sound
archives (mostly from Ecuador) sounded from the relatively pure, unmodulated
whistles of birds from w Panama, Costa Rica, and points north and west from
there. Nothing from those northern
populations sound anything, to my ears, like the tremulous, quavering songs of aequatorialis,
nor do the tracings from the spectrograms look anything alike. So, I think there’s definitely some
significant vocal differences between songs of triangularis versus the erythropygius
group and the aequatorialis group, and between the erythropygius
group and the aequatorialis group.
But, at this point, that’s a qualitative judgement on my part, and one
that still hasn’t been rigorously quantified with geographically broad samples
of homologous, spontaneously given vocalizations across the various taxa. Until we have that, I would favor sticking
with the status quo. Also, although I
clearly think it is premature at this point to be talking about English names
for any splits, I do want to point out that the suggested (in the Proposal) English
name of “Spot-throated Woodcreeper” for X. punctigula/insolitus is
already taken by Certhiasomus stictolaemus!”
Comments
from Jaramillo:
“NO. This is a highly complex situation that requires
much more rigorous data to sort it out. Looking at that line up of specimens is
eye-opening … that is a good amount of variation morphologically there. That
alone makes me think something more than one species is present, but which
ones, why, based on what data independent of morphology? I don't think we are
close on this one yet to understanding what is going on.”
Comments from Claramunt: “NO. First I have to
disagree with previous comments: plumage variation is suggestive of
species-level differences, in my opinion. At least the LSU series shows three
clearly diagnostic groups, easily distinguishable, that would match the
proposed three-species classification. Those differences are not minor in the
context of Xiphorhynchus woodcreepers that tend to be very conservative
in plumage patterns. But of course, the situation may be more complex and a
detailed study of geographic variation (including also songs and DNA) is
clearly necessary here before making decisions about species limits.”