Proposal (1044) to South American Classification Committee
Treat Formicarius destructus as a separate
species from F. nigricapillus
Effect on SACC list
If
this proposal passes, it will result in the elevation of the taxon destructus to full species, resulting in
a monotypic F. nigricapillus and a
monotypic F. destructus.
Background information
The
current SACC note reads”
"1c.
Areta & Benítez Saldívar (2025) provided vocal evidence for treating South
American destructus as separate species.
SACC proposal needed."
Areta & Benítez Saldívar (2025) summarized the
situation as follows:
The
Black-headed Antthrush (Formicarius
nigricapillus) includes two allopatric subspecies: nominotypic nigricapillus in Costa Rica and Panama,
and destructus in Colombia and
Ecuador (Ridgway 1893; Hartert
1898; Wetmore 1972; Krabbe and Schulenberg 2003, 2020). Although the taxon nigricapillus
was originally described as a full species by Ridgway (1893) and treated as
such by some authors (Chapman 1917, Cory & Hellmayr 1924), it was often
considered as a subspecies of the Black-faced Antthrush (F. analis) (Hartert 1902, Ridgway 1911). Conversely, the taxon destructus was originally described as a
subspecies of F. analis by Hartert
(1898) and was subsequently either considered as such (Hartert 1902), rarely
afforded species-level status (Salvadori and Festa 1899; Howell and Dyer 2022),
or most often considered as a subspecies of F.
nigricapillus (Chapman 1917, Cory & Hellmayr 1924, Wetmore 1972, Krabbe
& Schulenberg 2003).
New information
In
Areta & Benítez Saldívar (2025), we assessed species limits in F. nigricapillus using vocal, plumage,
and morphometric data, concluding that nigricapillus
and destructus are better treated as
two separate biological and recognition species. For more detailed explanations
and discussions stemming from historical taxonomic references, please refer to
the publication. What follows is a blend of selected copied and reorganized
text and images from Areta & Benítez Saldívar (2025) with some minor
adjustments to facilitate reading.
Songs: After discarding
duplicates, Areta & Benítez Saldívar (2025) compiled a total of 57 songs of
nigricapillus and 129 songs of destructus that were assessed aurally
and through examination of spectrograms. The song of nigricapillus is a
rapid series of around 25 clear, pulsated whistled notes that begins with a few
more spaced notes that become mostly evenly paced with a slight rise in pitch
halfway through the song and a relatively monotonous ending (sigmoid-like
spectrographic contour; Fig. 1). The song of destructus is a very rapid eerie series of around 40 ventriloquial
notes that fall and rise in pitch and decrease markedly in pace in the second
half (smile-like spectrographic contour; Fig. 1). The vocalizations of nigricapillus
and destructus have been described
accurately in field guides, but the importance of their differences has not
been fully realized. The song of nigricapillus
was described as "a rapid, pulsating series of ca. 20 deep, resonant,
whistled notes, the first 2-3 slower, more staccato, the next 6-8 rising in
pitch, the last 10-12 on the same pitch, with the final 2 notes slower, the
entire series lasting 4-5 sec" (Stiles and Skutch
1989, p. 287), while that of destructus "resembles that of
Rufous-capped Antthrush, but shorter, an eerie, quavering glissando of about 30
notes in 3 sec, sliding upscale and slowing noticeably at the end;
ventriloquial" (Hilty and Brown 1986,
p. 417). The song of nigricapillus has been aptly likened to
the shorter song of Thicket Antpitta Myrmothera
dives ( Garrigues and Dean
2007; Vallely and Dyer 2018), a comparison that does not apply to the song of destructus.
The
quantitative acoustic characterization evidenced that songs
of both taxa are 100% diagnosable (n=21 nigricapillus,
n=38 destructus). Acoustic data showed that 13 out of 15 variables differed significantly
between nigricapillus and destructus, the differences in 10 of
these 13 variables were very marked with non-overlapping mean ± SD,
automatically indicating that they belong to statistically different
populations. Taxon nigricapillus
showed lower song peak frequency, longer mean note duration and mean interval
between notes, fewer notes per song, slower pace, relatively even pace in the
first and second halves of the song, lower peak frequencies of first, median,
and final note, and longer duration of first, median, and final note. In
contrast, destructus had higher song
peak frequency, shorter mean note
duration and mean interval between notes, more notes per song, faster pace, a
marked deceleration in the second half of the song, higher peak frequencies of
first, median, and final note, and shorter duration of first, median, and final
note (Table 1). The songs of both taxa were clearly separated in
multivariate space (Fig. 2A) and a cluster analysis also revealed two
distinctive groups, unambiguously including all destructus samples
clustered separately from all nigricapillus recordings (Fig. 2B).
The
song of nigricapillus remains
essentially identical through ca. 490 km across Costa Rica and into C Panama in
our sample. t]The song of destructus also
remains basically the same through its distribution, ca. 1130 km extending from
NC Colombia to SW Ecuador. The diagnostic song types are separated by a gap of
ca. 190 km between NW Colombia (Jardín Botánico del Pacífico, Chocó) and
E Panamá (Nusagandi, Guna Yala), and exhibit no sign
of intermediacy closer to their respective limits (Fig. 1). Further documented
records are needed to properly understand the actual distributional gap between
nigricapillus and destructus. The width of the gap is at
least 190 km as shown by our song-recordings dataset, but possibly much
smaller: birds seen, heard, and tape-recorded at Cuchilla del Lago on the
Colombian side of the Serranía de Darién in the Cerro Tacarcuna (Renjifo et al.
2017) most likely represent the taxon nigricapillus. This would reduce the gap
between nigricapillus (Cuchilla del
Lago; see question mark in Figure 1) and destructus
(Reserva La Bonga) to 100 km within Colombia. Unfortunately, the sound
recordings were not available at the time of our writing and could not be
assessed (J. Avendaño in litt.). Further fieldwork should clarify the extent of
their allopatry and assess whether the Río Atrato and its formidable swamps act
as a biogeographic barrier for these taxa (Haffer 1970, 1975, Renjifo et al.
2017). The Cerro Tacarcuna records, if confirmed to be nigricapillus (which seems very likely), would indicate that both
taxa (nigricapillus and destructus) occur in South America.
Fig. 1. Plumage
aspect, songs, and geographic distribution of
songs of Black-capped Antthrush (Formicarius
nigricapillus), and Black-hooded Antthrush (F. destructus) analysed in this study. Orange circles: F. nigricapillus (photo: ML-452131711, San
Gerardo Biological Station, Costa Rica, by
Mark Hebblewhite; song: ML-220516, Reserva Biológica Bosque Nuboso
Monteverde, Costa Rica by D. L. Ross).
Blue circles: F. destructus (photo: ML-121617911, Rio Silanche Bird
Sanctuary, Ecuador by Nick Athanas; song: JIA-10, Reserva de Bosque Seco Lalo Loor, Ecuador by J. I. Areta). Circles
with a central dot denote songs measured quantitatively; plain circles denote
songs studied aurally (see Appendices 1 and S1); question mark (?) indicates
unconfirmed sound recording of nigricapillus
from Cerro Tacarcuna in Colombia. The differences in plumage (chestnut nape in nigricapillus, black nape in destructus), song, and morphometrics
collectively support the recognition of nigricapillus
and destructus as separate species.
Table 1. Acoustic parameters
of songs of Black-capped Antthrush (Formicarius
nigricapillus), and Black-hooded Antthrush (F. destructus). Values shown are mean ± SD [range], n= sample size.
Asterisk denotes significant statistical differences in the Mann-Whitney
non-parametric test (α<0.05), and plus symbol denotes non overlapping mean ±
SD. See Appendix 1 for measured sound recordings.
|
Variable |
F. nigricapillus (n=21) |
F. destructus
(n=38) |
|
Bandwidth 90% (Hz) |
205.35±56.37 [93.8-281.2] |
207.93±38.45 [140.6-281.2] |
|
Duration 90% (s)* |
2.38±0.33 [1.74-3.00] |
2.64±0.44 [1.92-3.88] |
|
Peak frequency (Hz)* + |
1484.37±61.75 [1406.2-1593.8] |
1689.91±61.7 [1546.9-1781.2] |
|
Mean note duration (s)* + |
0.06±0.01 [0.05-0.09] |
0.04±0.01 [0.02-0.07] |
|
Mean interval between notes (s)* + |
0.08±0.01 [0.05-0.10] |
0.04±0.01 [0.03-0.06] |
|
Number of notes*+ |
24.95±1.69 [22-29] |
37.62±5.57 [28-52] |
|
Sound density |
0.56±0.06 [0.46-0.67] |
0.6±0.08 [0.47 - 0.79] |
|
Pace*+ |
5.98±0.42 [5.44-6.96] |
9.61±1.09 [7.76-11.81] |
|
Pace change (second/first half)* + |
1.04±0.09 [0.88-1.19] |
0.76±0.07 [0.63-0.93] |
|
(8.63±1.2/11.37± 1.08) [5.61-6.67/5.25-7.58] |
(6.18±0.32/5.99±0.66) [6.82-11.46/9.02-12.82] |
|
|
Peak frequency first note (Hz)* + |
1345.97±68.13 [1218.8-1500] |
1650.24±93.23 [1406.2-1781.2] |
|
Peak frequency median note (Hz)* + |
1412.91±47.54 [1312.5-1500] |
1617.82±58.76 [1453.1-1781.2] |
|
Peak frequency final note (Hz)* + |
1477.67±60.46 [1406.2-1593.8] |
1703.12±69.11 [1546.9-1875] |
|
Duration first note (s)* |
0.04±0.02 [0.01-0.06] |
0.02±0.01 [0.01-0.03] |
|
Duration median note (s)* + |
0.09±0.02 [0.04-0.14] |
0.12±0.03 [0.04-0.10] |
|
Duration final note (s)* |
0.14±0.04 [0.10-0.26] |
0.11±0.03 [0.06-0.21] |
*=non-parametric Mann-Whitney test P-value <.05
+=non-overlapping mean ± SD
Plumage: To characterize the
external appearance of nigricapillus
and destructus, Areta & Benítez
Saldívar (2025) examined photographs of 37 museum
specimens, including the holotypes of both taxa, and vetted 40 good-quality
photographs on the citizen science platforms eBird (ebird.org) and iNaturalist
(inaturalist.org). They found that nigricapillus exhibits chestnut-brown
hindneck (sometimes extending to neck sides in a handkerchief or semicollar; Figure 1), and typically more chestnut-brown
back (Fig. 1), whereas destructus exhibits all-black hindneck and neck
sides (Fig. 1), and typically browner back. There is some variation in back
colour of specimens (but not in the back-neck contrast that distinguishes
taxa), with some nigricapillus being
seemingly identical in colour to typical destructus
(Chapman 1917,
USNM specimens). In some nigricapillus
individuals, the chestnut-brown hindneck is extensive and expands onto the
sides of the neck creating a semicollar, which gives
these individuals a capped aspect, that is less prominent in birds with less
extensive chestnut-brown hindneck. On the other hand, all individuals of destructus show a hooded aspect, caused
by its wholly black head, hind neck and neck sides (Fig. 1).
Fig. 2.
Quantitative analyses of songs of Black-capped
Antthrush (Formicarius nigricapillus),
and Black-hooded Antthrush (F. destructus). (A) Plot of the first two principal components (PC1 vs.
PC2) of the Principal Component Analysis. Ellipses depict 95% confidence
intervals. (B) Dendrogram from the agglomerative hierarchical
cluster analysis (UPGMA). Both methods consistently
show that nigricapillus and destructus differ markedly in songs
supporting their treatment as separate species. See Appendix 1 and S1 for songs
measured.
Morphometry: based on a limited
dataset (n=6 nigricapillus, n=9 destructus), Areta & Benítez
Saldívar (2025) concluded that 1) bill length (exposed culmen) showed no
overlap between taxa, with all individuals of nigricapillus having a longer bill than destructus, and therefore no overlap in mean ± SD values (Fig. 3a),
2) nigricapillus was longer winged
than destructus, with exact overlap
only in their extreme values, and no overlap in mean ± SD values (Fig. 3b), and
3) tail length was longer in nigricapillus
than in destructus, but the
difference was not statistically significant (two tailed t-test p=0.17) (Fig.
3c).
Fig. 3. Morphological measurements of Black-capped Antthrush (Formicarius nigricapillus), and
Black-hooded Antthrush (F. destructus).
Figure depicts median and quartiles on box plots. Asterisk denotes significant
statistical differences in one-way ANOVA (α<0.05). The
morphological differences in bill and wing length coupled to plumage
differences give support to the treatment of nigricapillus and destructus
as separate species. See Table 2 for sample sizes and data, and
Appendix 2 and S2 for specimens measured and studied.
The differences in songs and plumage herein
described can be readily appreciated in videos of free-ranging singing birds:
nigricapillus: https://macaulaylibrary.org/asset/608419951
destructus:
https://macaulaylibrary.org/asset/316228641
Taxonomic assessment
The
marked differences in vocalizations and morphology, and moderate but consistent
plumage differences strongly supports the elevation of the taxon destructus to species-level, leading to
the recognition of two allopatric and monotypic species, F. nigricapillus and F.
destructus. Areta & Benítez Saldivar (2025)
based their taxonomic conclusions on the recognition concept of species (Paterson 1985), whereas the same species would be recognized by applying
the biological species concept (Mayr 1963; “isolation
concept” fide Paterson 1985). The inferred level of discontinuity between nigricapillus and destructus is of such a magnitude that presumably any other modern
species concept would recognise them as separate
species, whether based on mating or other important attributes, phenotypic
distinctiveness, presence of autapomorphies, or phylogenetic independence
(Cracraft 1983, Mishler & Brandon 1987, Gill 2014, Areta et al. 2019,
Winker 2021). Howell & Dyer (2022:27) wrote that "Differences in plumage and song indicate that Central
American nigricapillus and South American destructus (Choco
Antthrush) are best treated as separate species." A view that is amply
supported by Areta & Benítez Saldivar (2025).
In
terms of plumage, the differences between nigricapillus
and destructus (Fig. 1) would be
among the least conspicuous for two Formicarius
species-level taxa, and comparable to (although less obvious than) those
between F. moniliger and F. analis. They differ most notably by
the presence of a rufous-chestnut fore-collar below the black throat in moniliger, whereas the black throat
contacts the grey chest directly in the two subspecies groups of F. analis
(Howell 1994, Vallely and Dyer 2018). However, less obvious plumage differences
exist between the analis and hoffmanni subspecies groups within F. analis despite their noticeable vocal
differences (Howell 1994) which are compatible with species-level differences
in the genus (Krabbe and Schulenberg 2003, van Dort et al. 2023, Benítez
Saldívar & Areta in prep.).
Common names
Most
species in the genus Formicarius
carry common English names that refer to plumage features. We propose to adopt
the name Black-capped Antthrush for F.
nigricapillus and Black-hooded Antthrush for F. destructus, which focus on one of the main plumage differences
between them and retain a connection to the former Black-headed Antthrush used
for the composite species. We find the proposed use of Black-hooded Antthrush
for F. nigricapillus by Howell and Dyer (2022) to be misleading, as this taxon is capped rather than
hooded. The smaller bill of destructus
is difficult to appreciate in field conditions, and bill features do not seem
useful to coin common names here. Finally, Choco Antthrush has been proposed
for destructus (Howell and Dyer 2022); although a good name, there are other antthrushes in the
Choco, and it loses the connection to the former Black-headed Antthrush name.
Voting and
recommendations
Perhaps
the best thing to do is to vote on three different aspects of the proposal:
A) Species limits: We
recommend a YES vote to split F.
destructus from F. nigricapillus.
B) English names: We
recommend a YES vote to adopt the name Black-capped Antthrush for F. nigricapillus and Black-hooded
Antthrush for F. destructus
C) Presence of nigricapillus in Colombia. A lingering
question is whether the Cerro Tacarcuna records in Colombia should be
provisionally considered to be nigricapillus
until shown otherwise. For biogeographic reasons, we lean towards the
maintenance of nigricapillus in the
SACC list based on these records, as it seems unlikely for destructus to reach the Cerro Tacarcuna crossing the Atrato swamps.
We recommend a YES vote to keep F.
nigricapillus in the SACC list.
References
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Links to supplementary
information:
Addendum:
Genetics: The coincidental
break in plumage and vocalizations between F.
moniliger and F. analis umbrosus
(a representative of the hoffmanni
group) were used as arguments to support the elevation of moniliger to species status (Howell 1994). More recently, phylogenetic data have shown that F. moniliger is sister to a clade
including F. destructus as more
closely related to F. analis
(including representatives of the hoffmanni
and analis subspecies groups) (Harvey et al. 2020). This distant relationship between moniliger and analis
further reinforces the species-level split of F. moniliger and lends support to vocal differences as a useful
tool to establish species limits in Formicarius.
Although there are no available genetic data for nominotypic nigricapillus, the vocal distinctions
between nigricapillus and destructus seem as or more marked than
those between F. moniliger and F. analis of the analis and hoffmanni
subspecies groups. In our paper we predicted that nigricapillus and destructus
will exhibit levels of genetic differentiation tantamount to their vocal and
morphological distinctions.
The
Formicarius phylogenetic tree from
Harvey et al. 2020:
Harvey
MG, Bravo GA, Claramunt S, et al. (2020) The evolution of a tropical
biodiversity hotspot. Science 370: 1343–1348.
Juan
I. Areta and M. Juliana Benítez Saldívar, April 2025
Voting chart: https://www.museum.lsu.edu/~Remsen/SACCPropChart1044+.htm
Comments
from Remsen:
“A. YES. Although
playback trials would be nice, the degree of difference in the songs is
consistent with species rank, and burden-of-proof falls on those who would
treat them as subspecies.
“B. MAYBE, for all the
good reasons outlined in the proposal, especially maintaining the connection
between old and new names. Also, follows
SACC guidelines (https://www.museum.lsu.edu/~Remsen/SACCEnglishNameGuidelines.pdf)
for providing new names for both daughters in a parental split. After having looked through Macaulay photos
of dozens of destructus, “hooded” seems especially appropriate for the
extent of the black. The match between
the scientific and English names for nigricapillus is helpful in remembering
both. However, as for nigricapillus,
a problem is that “capped” is typically used for cases in which the bird has a
much more distinctive color patch on the top of the head, which is not really
the case for nominate ruficapillus, despite the scientific name. Obviously, the scientific name reflects a
pattern seen on specimens, but I think we need side-by-side photos of the
specimens, if only as confirmation that the name is OK.
“C. YES, but somewhat
reluctantly because the recordings are unavailable and because perhaps the
Colombian national committee should have the say on this one. On the other hand, to propose that the
records are not nigricapillus makes no biogeographic sense, and I agree
with this statement in the proposal “Cerro Tacarcuna records in Colombia should
be provisionally considered to be nigricapillus
until shown otherwise.”
“Anecdote: puzzled by
the name destructus, I looked at Jobling (online), and here is the
derivation from Hartert’s 1898 description: ‘very much destroyed by the shot, but still quite recognizable, is so
considerably smaller and darker brown above than typical analis that I
do not hesitate to distinguish it subspecifically’.”
Comments
from Lane:
“I must admit this one was not on my radar (although I have seen, and heard,
both taxa). The voices are much more distinct that I was expecting, and I think
the results of the study presented are good.
“A) YES to splitting
the two members of the complex as biological species.
“B) The two daughter
species are not all that strongly differentiated by plumage, and really can't
see F. nigricapillus having a distinctive black crown set off against
the rest of the head (I suspect the name was coined because it was
blacker-crowned than F. analis... and granted, I am looking at the
poorly-lit Macaulay photos rather than specimens to make this statement), but
unless we want to get derailed by another English name situation, I will go
with the names suggested: Black-crowned and Black-hooded.
”C) YES to retaining
both species in the SACC area due to the records from the border near Panama.”