Proposal (1058) to South
American Classification Committee
Treat the
spodionota subspecies group as a separate species from Silvicultrix
frontalis.
Effect
on SACC:
This would split an existing species on the SACC list into two species.
Introduction: SACC has been asked
to do this proposal because the IOC list treats them as two species, citing
Moreno et al. (1998) for support.
However, they are treated as conspecific by Clements, Howard-Moore, and
HBW-BLI lists. I did not have this issue
on our proposal “do list” because it is based largely on Moreno et al.’s
comparative genetic distance using mtDNA sequence data (350 BP ND2).
Our
current SACC note reads:
120. García-Moreno et al. (1998)
suggested that the plumage and genetic differences between the frontalis
and spodionota subspecies groups warranted species-level recognition for
each.
Background: Silvicultrix (ex-Ochthoeca)
frontalis has traditionally been treated as a single species that occurs
in the humid Andes from n. Colombia to c. Bolivia, e.g., from Cory &
Hellmayr (1927) through Meter de Schauensee (1970) and Fjeldså & Krabbe
(1990) to AviList (2025), with 3-5 subspecies:
• albidiadema:
Eastern Andes of Colombia
• frontalis:
Central Andes of Colombia south to western Andes in n. Ecuador, but see next:
{• orientalis}:
Eastern Andes from n. Ecuador to c. Peru (subsumed by Traylor [1985] into nominate
frontalis)
• spodionota:
Eastern Andes in c. Peru (Junín to n. Cuzco) but see next:
{• boliviana}:
curiously patchy and taxonomically “impossible” range, interrupted by spodionota:
Andes from c. Peru south to c. Bolivia; see Traylor (1985) for full details on
this taxonomic conundrum, but briefly, recognizing boliviana splits it
into two allopatric and evidently phenotypically indistinguishable populations,
but treating this as a synonym of spodionota makes the latter split into
3 populations with a leapfrog pattern of phenotypic variation, the central one
diagnosably different from the populations to north and south; then, there is
also the unnamed Cordillera Vilcabamba population, which according to Traylor
is the most distinctive of all with most individuals without wingbars … like
the frontalis group. Broadly
defined spodionota would thus be just as uncomfortable as recognizing
disjunct populations of boliviana as the same taxon in that it would
have four diagnosable populations, each possibly a PSC species. This one will be exceptionally interesting to
study genetically.
Traylor
(1985) provided rationale for their treatment as conspecific pending study of
the contact zone in central Peru.
Below
is John Fitzpatrick’s plate from Traylor (1985 – the original is much better
than reproduced here). I have blacked
out Silvicultrix pulchella to reduced noise, but I have left in the
taxon jelskii of the western Andes of extreme s. Ecuador and nw. Peru;
currently treated as a separate species, it has been treated as a subspecies of
both S. frontalis and S. pulchella. Harvey et al. (2020) showed that it is sister
to S. pulchella, not S. frontalis/spodionota.
New information: Obviously not very new but García-Moreno et al. (1998) in a study of
the phylogeny of chat-tyrants used 320 bp on mtDNA (ND2) to produce the
following phylogenetic hypothesis:
This was 1998, so cut them a lot of slack on the
weak genetic sampling – this was top-of-the-line stuff back then. They showed that frontalis and spodionota
groups were sister taxa with modest support.
García-Moreno et al. (1998) argued for their treatment as separate
species based on comparisons of relative genetic distance, including alluding
to broader comparisons of many taxa of Andean forest birds.
As noted by Traylor (1985) and García-Moreno et
al. (1998), the putative contact zone between the northern frontalis
group and the southern spodionota group is somewhere in that 150 km long
region of Dpto. La Libertad from which there are almost no bird samples and in
which there are no known biogeographic boundaries (See recent SACC Pionus
proposal). Knowing what happens at the contact zone would presumably provide an
immediate “answer” to taxon rank in this case, i.e. abrupt turnover with little
sign of gene flow or a hybrid swarm. For
now, it’s anyone’s guess. The main
phenotypic difference is the absence (frontalis) or presence (spodionota)
of rufous wingbars.
Here is the rationale presented by García-Moreno
et al. (1998):
“Traylor (1985) identified a gap of 150 km
between the southernmost frontalis in La Libertad and the northernmost spodionota
a little north of the Huallaga Gap in Huánuco, and decided to treat them as a
single species until information was obtained about how they interact in a zone
of sympatry. This segment of the Cordillera Central remains poorly explored,
thus the taxa are recognized currently as subspecies. However, the genetic
differences between them (0.059, including 4 tv) is of a level comparable to that
of fully recognized species(e.g., S. diadema and S. jelskii:
0.063, O. leucophrys and O. oenanthoides:0.042; Table 1).
Although we do not think that species status can be diagnosed solely on the
grounds of a quantity of molecular or morphological divergence, we believe that
the mtDNA divergence together with biogeographic separation and plumage
differentiation suggest that they are different species: S. frontalis
(including subspecies albidiadema and orientalis) and S.
spodionota (including subspecies boliviana). It should be noted that
the Southern taxa (spodionota and boliviana) are phenetically
very similar to S. jelskii, whereas the northern S. frontalis
albidiadema is characterized by the absence of wingbars and rufous fringes
on the tertials (this could be a derived character state; however, a similar
lack of wing-pattern also is found within S. spodionota in western Cuzco
and Ayacucho).”
Discussion
As far as I can determine, there is no hint that
the two groups differ vocally, although this might be because there isn’t much
to work with. These birds are usually
silent, and their voice is a short trill.
Boesman did not attempt and analysis, and there is no hint in
Schulenberg et al. (2007) (or anywhere else I’ve looked) of vocal
differences. That of course does not
mean that critical differences don’t exist – only that we don’t know yet.
My superficial check using xeno-canto provide an
N=1 possibility that those differences exist:
The only recording in xeno-canto of the song of spodionota
group is a good one of boliviana from Dpto. La Paz by Dan Lane:
https://xeno-canto.org/species/Silvicultrix-spodionota
Note the separated notes at the end of the
trill.
In contrast, here is a typical song from the frontalis
group from Ecuador:
https://xeno-canto.org/species/Silvicultrix-frontalis
This represents is the way the song is usually
rendered phonetically in field guides.
Note the lack of separate notes at the end, which only has a slight
“hump” in the steady trill.
This has no meaning pending an analysis of a lot
more recordings, especially from the central Peruvian population of boliviana’s
range and, most critically, from spodionota itself, which would be the
type species if we recognized S. spodionota. At this point, for all we know there could be
different songs for Peruvian frontalis south of the Marañon, Peruvian boliviana,
spodionota, and Bolivian boliviana. Or no consistent variation at all.
Because voice is critical in species limits
assessments in the Tyrannidae, I do not think that there is any evidence to
change the status quo at this time. The
plumage differences are suggestive but not conclusive of anything beyond
subspecies rank. The genetic data (a
tiny BP sequence of one mitochondrial gene) is inadequate for making taxonomic
decisions of any kind. Thus, I strongly
recommend a NO on this based on current evidence. I also see no need to rush this because
eventually we will likely have conclusive evidence from the uncontacted contact
zone. Also note that the difference in
presence/absence of wingbars as a species-level character is rendered
problematic by the Vilcabamba population of spodionota, which lacks wingbars –
see plate above.
Literature Cited: (see
SACC Biblio for others):
GARCÍA-MORENO, J., P. ARCTANDER, AND J. FJELDSÅ. 1998.
Pre-Pleistocene differentiation amongst chat-tyrants. Condor 100: 629–640
https://digitalcommons.usf.edu/cgi/viewcontent.cgi?article=13795&context=condor
TRAYLOR, M.
A., JR. 1985. Species limits in Ochthoeca diadema
species-group (Tyrannidae). pp. 430-442 in "Neotropical
Ornithology" (P. A. Buckley et al., eds.) Ornithological Monographs No.
36.
Van Remsen, June 2025
Note from Remsen on English names: If the taxonomic proposal passes, then we’d need a separate English
name proposal. IOC retained “Crowned
Chat-Tyrant for the frontalis group even though it’s range is not substantially
larger than that of spodionota and used “Kalinowski’s Chat-Tyrant” for
the spodionota group.
Vote tracking chart:
https://www.museum.lsu.edu/~Remsen/SACCPropChart1044+.htm
Comments from Niels Krabbe (guest voter): “YES. I
see that the sequences used by Garcia-Moreno et al. (1998) have not been
uploaded to GenBank, which I find most unscientific. Also, the number of bp
compared is low for today's standards.
“However, Winger and Bates (2015) gave complete (1041 bp)
sequences for the same (ND2) gene for a number of specimens of frontalis (from
E Carchi, Imbabura, W Pichincha, and Morona-Santiago, Ecuador, and San Martín,
Amazonas, Cajamarca, Huanuco and Apurímac, Peru). I
took the trouble to compare these sequences.
“The difference between frontalis (from Ecuador and N Peru)
and spodionota (from Huánuco, Pasco and Apurímac) is as high as 6%.
Furthermore, sequences from spodionota from Huánuco/Pasco (Unchog,
Millpo) and Apurímac are virtually identical. Only the Millpo bird differs very
slightly (one transition in 1041 bp). Birds from both N and C Ecuador (E
Carchi, Imbabura, Cotopaxi, Morona-Santiago) are also virtually identical to
each other (Imbabura bird differs by one transition in 1041 bp), whereas they
differ from N Peruvian birds by about 1%. N Peruvian birds still differ from C
and S Peruvian birds by 6%.
“The distinct genetic and morphological difference between
frontalis and spodionota lead me to think it safe to rank them as different
species.”
Winger, B. M. and Bates, J. M.
2015. The tempo of trait divergence in geographic isolation: Avian speciation
across the Marañon Valley of Peru. Evolution 69 (3): 772–787.
Comments from Andrew Spencer: “I wanted to offer some unsolicited
comments on the Silvicultrix frontalis split proposal and add some
observations/quick analysis on the vocalizations of the two groups. Hopefully
this will add some information for those voting on the issue. None of this is
published of course, sample sizes are small, and geographic coverage not the
best, but here you go:
“Back when I was guiding in the Andes, I noticed while Ecuadorian
birds would often respond somewhat nicely to playback when I was trying to show
clients the species, those in central and southern Peru were much less
cooperative. Digging further after one frustrating experience, I realized all
the cuts I was using were from Ecuador, and so I found a recording (I don't
remember which at this point) of the southern population to try. Later in
the trip I used that recording, with the birds responding much better. This is
in spite of the overall vocalization sounding superficially quite similar. I
filed this away as "interesting, I'll dig into this later", and then
promptly forgot to do anything of the sort.
“On a post-guiding career trip to central Peru, I spent some more
effort trying to get recordings of chat-tyrants. I eventually managed to find a
couple of birds that were actually vocalizing naturally at dawn, seemingly
while having a territorial dispute. Unfortunately, they quickly became quiet,
and subsequent recordings I obtained were after playback. This did remind me
though that I needed to look into vocal differences between the northern and
southern groups, which I did at the time, but then again filed away under the
"someone should publish on this" excuse.
“So, all that said, I do think that at least some of the
vocalizations of the northern and southern groups of S. frontalis are
consistently and diagnostically different. I primarily looked at what I think
of a song in the species. There's always the risk that I'm not comparing
entirely analogous vocalizations, or that there is hidden complexity in the
repertoire muddying the picture that would become apparent with a larger sample
size. But I don't think that's the case here.
“To summarize, I think there are two (or three, depending how you
separate features out) important and consistent differences in the songs of
these taxa that are diagnostic.
“Van in his proposal has pointed out one difference: the
additional sputtering phrases after the initial longer trill. This is
apparently not always present (see the first example in the spec comparison,
below), but 3 of 4 samples I found do have it. Tied to this is the less regular
frequency pattern over the course of the song. The spodionota group,
while generally descending over the length of the song strophe, has a lot of
ups and downs. In the frontalis group, the song generally descends much
more smoothly, before having the slight "hump" noted by Van near the
end of the song.
“The other important difference is the overall pitch of the song,
especially the intro notes. These are notably higher-pitched in the spodionota
group than in the frontalis group. In the spec below, I have red
horizontal lines covering the highest and lowest frequencies in the spodionota
group, and blue lines doing the same for the frontalis group. Note how
the peak of the intro notes for spodionota are around 10.5-11 kHz,
whereas those of frontalis are between 7.5-8 kHz. Also note how the
majority of the energy in the song strophes averages quite a bit higher for
the spodionota group - in most samples almost entirely above
the song of the frontalis group.
“There are all the usual caveats for these poorly recorded birds,
including that it's unknown what happens in the gap between the northernmost
recording of the spodionota group in Huánuco and the southernmost of the
frontalis group in Amazonas. That said, in my opinion, the combination
of plumage differences, molecular data, even if rather dated, and vocalizations
all support a split.
“Recordings used in the spec comparison, left to right:
spodionota group:
ML633678529, Huánuco, Peru
ML470360571, La Paz, Bolivia
ML470352611, Cuzco, Peru
ML143651, Cuzco, Peru
frontalis group:
ML222114391, Pichincha, Ecuador
ML44533211, Imbabura, Ecuador
ML58284, Carchi, Ecuador
ML269800, Caldas, Colombia
Comments from Lane: “NO. This
is another case of a very weak study suggesting an interesting taxonomic puzzle
without providing enough evidence to clarify what is actually going on.
Garcia-Moreno et al. simply didn’t have enough sampling to make much sense of
the variation within S. frontalis, and an mtDNA study with 320 bp is
very little information. I will vote NO on this simply because the study simply
doesn’t offer much to vote on!
“My voice comparisons have been
strictly with the drawn-out trilled vocalization. This vocalization is what I
term the “daytime song” which is not the same as the dawn song that seems to
dominate in many Silvicultrix recordings by most other field-workers,
and it consists of single “tink” notes. I’ve made
efforts to record the daytime songs of Silvicultrix whenever I can and
have learned that my comments in Birds of Peru are not accurate (and were
written as a result of my ignorance some 20 years ago). With regards to voice,
my observations largely agree with what Andrew Spencer has written, although I
believe that bolivianus is distinctive within the southern group. See
recordings here: https://media.ebird.org/catalog?mediaType=audio&view=grid&taxonCode=crocht1https://media.ebird.org/catalog?mediaType=audio&userId=USER155017&view=grid&taxonCode=crocht1
and here: https://xeno-canto.org/species/Silvicultrix-spodionota
“Van mentions my cut from La Paz (https://xeno-canto.org/150430, https://macaulaylibrary.org/asset/638812141, https://macaulaylibrary.org/asset/470360571 all the
same cut, but the last is “unconfirmed” within eBird due to being on a
historical checklist that was flagged as too long by a reviewer), but I also
have recordings of the same song type from Manu Road in Cusco (https://macaulaylibrary.org/asset/470352611) and
Cochabamba, Bolivia (https://xeno-canto.org/145014). So. I
think it’s safe to say that this song with the repeatedly rising-falling
terminal section is characteristic of S. f. boliviana and makes a case
for the taxon to be a good one (at least from Cusco south and east into
Bolivia). I have few recordings north of Cusco, and there are few others from
central Peru aside from Andrew’s and one or two more. These cuts suggest that
there is no rising-falling terminal section to the daytime songs of these
birds, but birds from Huánuco (https://xeno-canto.org/40518, and
Andrew’s cuts noted above) seem to be still higher-pitched and “weaker” than
those from Amazonas (https://macaulaylibrary.org/asset/305709521, https://xeno-canto.org/131757 same cut
in both) and north of the Marañon (https://xeno-canto.org/704098, https://xeno-canto.org/5905, https://xeno-canto.org/121067). The
relative lack of samples makes it difficult to say much about the amount of
variation within and among individuals, so I will refrain from doing so.
Overall, my impression is that there is much more going on here than just
splitting S. frontalis into two, and the Garcia-Moreno et al. paper
simply doesn’t address the issue in any meaningful way. Until we have more
information, I think it best we wait for additional information (both
molecularly and voice) to make an educated decision on what’s going on here. To
split based on the current knowledge is a shot in the relative dark and may
result in something we’ll have to reverse as more information comes to light.”
Comments from Areta: “I vote YES to split spodionota
from frontalis. The congruent
genetic, plumage, and vocal data support the division. I would of course prefer
a proper taxonomic paper dealing with all the details and benefiting from more
samples, but the data seem enough to act. The unnamed Vilcabamba population is crying
out to be studied and named.”
Comments from Robbins: “Given
current information I’m on the fence on this one. Given that the plumage of
southern O. f. spodionota is more similar to S. jelskii
than nominate frontalis, yet Harvey et al (2020) have shown that the
latter is more closely related to pulchella, I consider plumage not to
be a good indication of relationships in Silvicultrix.
“The
ND2 data (thanks Niels for bringing in the additional information), are
suggestive, but I think most of us would agree that nuclear data are needed for
all Silvicultrix.
“With
regard to vocalizations, more information is needed, especially if perhaps some
of these comparisons are not of analogous vocalizations, e.g., dawn song vs.
post dawn song.
“I
think there may well be two species within the currently recognized frontalis,
but we need more information. So, for now I vote to wait until those data are
available.”
Comments from Stiles: “YES to split spodionota from
frontalis given recent genetic data, plumages, voice.”