Proposal (1052) to South American Classification Committee
Revise species limits
in South American Bubo owls
Background: Proposal 328 was a first attempt
laid out before SACC to change the taxonomy of Great Horned Owl (Bubo
virginianus) in splitting off the austral form B. (v.) magellanicus
as its own species. The complex had first been reviewed by Traylor (1958), who
laid out the distribution and known taxonomy of the South American populations,
with a northern Andean subspecies (nigrescens, type locality: “Cechce”
<sic: Ceche, Chimborazo; Paynter 1993>, Ecuador), a southern Andean and
Patagonian subspecies (magellanicus, type locality: Tierra del Fuego), a
lowland savanna subspecies (nacuturu, type
locality: Paraguay; including scotinus from Caicara, Rio Orinoco, Venezuela, and elutus from Lorica,
Bolivar, Colombia), and a caatinga form (deserti
from Salitres, near Joazeiro,
Bahia, Brazil). As Mark Robbins has laid out the situation of the taxonomy of
the group in the previous proposal, I won’t run over it much further here.
However, largely due to a set of confounding recordings by Ted Parker from the
northern Andes of Peru (Cerro Cruz Blanca, Piura) associated with a specimen at
LSU (LSUMZ 97577) that has been identified as “Bubo virginianus nigrescens?”
(see images), the SACC rejected the proposal at the time. These recordings
seemed to represent a population of Bubo in the Andes of northern Peru
that shared both “northern” and austral song types.
Since
then, multiple authorities have supported the split, including Clements
checklist (Clements et al 2025)—and by extension, eBird—, IOC checklist (Gill
et al 2025). This split within the American Bubo has been proposed by
various authors due to the distinctive song and smaller size of the austral B.
(v.) magellanicus (e.g., Koenig et al. 1999, Jaramillo 2003, Pearman and
Areta 2020). The first publication on the genetics of the complex (Ostrow et
al. 2023) showed a deep branch between B. (v.) magellanicus (including
samples from as far north as the Andes of Peru) and the remainder of the B.
virginianus complex, though not without some messiness. So, it is time for
SACC to re-evaluate the situation.
Analysis: At the time that Mark
drew up Proposal 328, we had been stymied by the absence of better voice and
genetic specimen sampling along the northern Andes. Since that time, two papers
have reviewed both the vocalizations of the American Bubo (López-Lanús
2015) and the genetics (Ostrow et al. 2023). Both have supported the split of B.
magellanicus from B. virginianus but have not suggested any further
changes to the taxonomy within the latter. In addition, new recordings, from
Ecuador and Colombia, have been added to Macaulay Library (see below). I will
discuss the voice and the molecular studies separately below.
Voice: So, the first thing to
assess is each of these new papers. López-Lanús (2015) did an exhaustive
analysis of the vocalizations of all populations of the Bubo virginianus
complex from Alaska and Canada south to Tierra del Fuego using online sound
archives (Macaulay Library and Xeno-canto). He concluded that there were five
song types represented: (1) the widespread North American voice (hereafter
called “virginianus”), (2) the Patagonian magellanicus, (3) savana
nacaturu, and (4) northern Andean nigrescens,
and (5) also considered the Parker recordings mentioned above to represent an
undescribed sixth voice type (which he called “Ñécu”).
Interestingly, the virginianus voice is very strongly conserved
throughout North America and is diagnosably different in pattern (sex for sex)
from both nacuturu and nigrescens. I
should point out, that in López-Lanús’ study, the least represented population
in the sound collections he checked was nigrescens with N=4. Since that
time, additional recordings have been archived, particularly in Macaulay
Library, and these are key to the situation with nigrescens and magellanicus!
Importantly, these recordings include several with duets, which apparently are
the circumstance when nigrescens gives the puttering series that Parker
recorded in Piura and that is so similar to magellanicus. These
recordings of the puttering duet span the distribution of nigrescens
from the Eastern Andes of Colombia to Piura, Peru:
ML cuts of B. v. nigrescens giving
puttering notes like B. magellanicus: ML616192787 (Cundinamarca,
Colombia), ML307206661 (Azuay, Ecuador), ML582374191 (Cañar, Ecuador), ML573946951, ML617182690 (Pichincha, Ecuador), ML21879, ML21880, ML21890 (Piura, Peru). See map
figure.
It
is this song type that López-Lanús (2015) considered his “new” voice “Ñécu!” Apparently, it is actually a representative song
type over the entire distribution of B. v. nigrescens, and this may
require a new view on the relationships of that taxon.
Genetic
analysis: Ostrow et al. (2023) used both nuclear UCEs and mtDNA over a
large area of both the North and South American distribution of the Bubo
virginianus complex, although I should note that North American samples
greatly outnumbered South American; some specimens were strictly sampled from
toepads (including 2 nigrescens and 2 magellanicus). The sample
sizes of the South American taxa were reported as: nigrescens 3, nacuturu 1, magellanicus 6. However, I must
point out that one of the “nigrescens” (a toepad sample) was from La
Guajira, Colombia, and therefore was actually a nacuturu.
This translates to an actual sample of nigrescens 2, nacuturu
2, and magellanicus 6. In Ostrow et al. (2023), this misidentification
resulted in nigrescens being paraphyletic in their Figure 2 (all
samples) which is a maximum-likelihood UCE tree, with the La Guajira sample
being sister to the “single” nacuturu sample, although
this now makes sense as both samples were nacuturu.
On
the “all samples” tree, the nacuturu branch
comes out within the North American virginianus group among samples that
are largely from the southwestern USA and Middle America. Sister to the North
American/nacuturu group is nigrescens,
with magellanicus sister to this entire clade. In the “fresh tissues
only” tree of Figure 2, the North American clade is sister to nacuturu (so: the two are monophyletic with respect
to one another) with nigrescens sister to them and magellanicus
sister to that entire clade. Figure 3 of Ostrow et al. is a maximum-likelihood
tree using mtDNA. This tree has the North American virginianus as a
monophyletic clade with its sister being nigrescens and a specimen of magellanicus
(from Lima, Peru). Sister to these clades is nacuturu
(including the misidentified “nigrescens”), and finally, the branch with
the remainder of magellanicus. Ostrow et al (2023) concluded that there
was still gene flow between nigrescens and magellanicus (both
Andean taxa) in Peru, and also (some gene flow between one of the nigrescens
(Cauca, Colombia) and North American birds (!).
These molecular results have me
scratching my head a bit: the trees presented in the main paper of Ostrow et al.
(2023) seem not to have concordant branching among the North American birds, nacuturu, and nigrescens, but all or the bulk
of magellanicus is always sister to that entire clade. But the positions
of nacuturu and nigrescens with respect
to the North American birds switches depending on the tree, and a Peruvian magellanicus
is on the nigrescens branch on the mtDNA maximum-likelihood tree. I
can’t imagine that nigrescens and North American birds are currently
experiencing gene flow across the Darien (nor have they in a long time!).
Recommendation: The publications since
Mark’s proposal have made a bit of a hash of the distribution and taxonomy of
the complex, in part because of errors in assigning names to populations, in
part due to missing data that have since become available. The voice and phylogenetic
placement of B. magellanicus with respect to the rest of the B.
virginianus complex seems to make a strong argument that it should be
recognized as a separate species. However, there appears to be molecular
evidence of continuing gene flow between magellanicus and nigrescens
in Peru AND the vocal repertoire of nigrescens actually contains the
puttering component that makes magellanicus so distinctive. Finally,
even though nacuturu and nigrescens are
both later branches off the main B. virginianus tree with respect to B.
magellanicus, each clade has distinctive voices compared to the virginianus
voice, and neither is actively experiencing gene flow with populations of the
North American virginianus group. My gut feeling is that we should
divide up the B. virginianus complex into four species: B. virginianus
(all taxa south to Panama), B. nacuturu
(lowlands of South America, including the populations named scotinus,
elutus, and deserti, the validity of
which remains to be reviewed), B. nigrescens (Andes of Colombia to
Piura, Peru), and B. magellanicus. Either this or continue to maintain
the full group as one species, as it seems that nigrescens and magellanicus
share the “distinctive” puttering that has been the main character used to
separate the latter from the remaining complex, and that Ostrow et al. found
evidence of continuing gene flow between the two in Peru. But comprehension of
the molecular results of Ostrow et al is not exactly in my wheelhouse, so I
will leave it to those on the committee who can address them and how best to
vote. So, these are the options I see:
A)
Maintain
Bubo virginianus with all of the South American populations within it
until their relationships are better understood (this seems the least helpful,
I recommend NO).
B)
Separate
B. magellanicus from the remainder of B. virginianus (this seems
the favored stance by most other authors and lists, but leaves some mess swept
under the rug, I recommend YES).
C)
Also separate B. nacuturu
and B. nigrescens from B. virginianus, now restricted to North
and Middle America (given the voice distinctions, especially compared to the
surprising conservativeness within North American populations, I am inclined to
recommend YES).
Literature
Cited
Clements,
J. F., P. C. Rasmussen, T. S. Schulenberg, M. J. Iliff, T. A. Fredericks, J. A.
Gerbracht, D. Lepage, A. Spencer, S. M. Billerman, B. L. Sullivan, M. Smith,
and C. L. Wood. 2024. The
eBird/Clements checklist of Birds of the World: v2024. Downloaded from https://www.birds.cornell.edu/clementschecklist/download/
Gill
F, D Donsker & P Rasmussen (Eds). 2025. IOC World Bird List (v15.1).
Jaramillo, A. 2003.
Birds of Chile. Princeton Univ. Press, Princeton, New Jersey, USA
König,
C., F. Weick, and J-H. Becking.
1999. Owls. A guide to the owls of the world. Pica Press, Sussex, England.
López-Lanús, B. 2015. Análisis domparativo de las vocalizaciones de
distintos taxa del género Bubo en América. Hornero 30:69-88.
Paynter, R. A. 1993.
Ornithological Gazetteer of Ecuador, second edition. Museum of Comparative
Zoology, Harvard University, Cambridge, Massachusetts, USA.
Ostrow, E. N., L. H. DeCicco, and R. G. Moyle. 2023.
Range-wide phylogenomics of the Great Horned Owl (Bubo virginianus)
reveals deep north-south divergence in northern Peru. PeerJ 11:e15787
http://doi.org/10.7717/peerj.15787
Pearman, M. and J. I.
Areta. 2020. Birds of Argentina. Princeton Univ. Press, Princeton, New Jersey,
USA
Roesler, I. (2024).
Lesser Horned Owl (Bubo magellanicus), version 1.1. In Birds of the
World (S. M. Billerman and F. Medrano, Editors). Cornell Lab of Ornithology,
Ithaca, NY, USA. https://doi.org/10.2173/bow.grhowl2.01.1
Schulenberg,
T.S., D. F. Stotz, D. F. Lane, J. P. O'Neill, and T. A. Parker, III. 2007. Birds of Peru.
Princeton Univ. Press, Princeton, New Jersey, USA.
Traylor, M. A. 1958.
Variation in South American Great Horned Owls. Auk
75:143-149.
Dan Lane, May 2025
___________________________________________________________________________________________________
Vote tracking chart: https://www.museum.lsu.edu/~Remsen/SACCPropChart1044-.htm