Proposal (978)
to South
American Classification Committee
Treat the two
subspecies of Parabuteo unicinctus as separate species
Background
and Current taxonomy
Parabuteo
unicinctus
currently consists of two subspecies, P. u. unicinctus (Bay-winged Hawk,
Temminck 1824) and P. u. harrisi (Harris’s Hawk, Audubon 1837). From 1837, these two were generally placed in
different genera (about 14 different genera) and, uncommonly, in the same genus
(Craxirex 1861-1866, Antenor 1875-1882). They were finally
stabilized in Parabuteo (1916 to
1922).
These subspecies differ by size, range, and plumage
variation. Unicinctus is distinguished from harrisi by having a dark
brown ventrum streaked or flecked with white or whitish, a smaller body and a
longer tail (Dwyer and Bednarz 2020).
Their
ranges are traditionally thought to be:
• P. u.
unicinctus is resident from ne. Colombia
and w. Venezuela south through e. Bolivia and central and ne. Brazil to
s.-central Chile and s. Argentina.
• P. u. harrisi is
resident from se. California, east to central Texas and south throughout n.
Mexico, then south along the Pacific slope from w.-central Mexico to El
Salvador and from Nicaragua to w. Colombia, w. Ecuador, and w. Peru.
New information
Clark and Seipke (2023) presented compelling new morphological
data, and they reviewed the behavioral and DNA data, all supporting the
elevation of these two subspecies to species status.
Morphological Data
Adult and
juvenile plumages differ between the two subspecies. For adult birds, these include throat markings, color
and markings on the undersides of the remiges, markings on the belly and
breast, markings on the leg feathers, and extent of white at the base and tips
of the rectrices.
In juvenile birds, consistent color differences occur in
underparts, undertail, upper back, upperwing coverts, and underwing
coverts. In addition, P. (u.) unicinctus
has delayed plumage maturation with four distinct age classes, and Clark and
Seipke (2023) provide the first detailed descriptions of Basic II and Basic
III, which are similar in body plumage to juvenile P. (u) harrisi.
See power point by Clark and Seipke.
Ecology
Harrisi individuals hunt and
breed cooperatively. Although some
examples of co-operative breeding have been noted in unicinctus, there
have been no examples noted of co-operative hunting.
DNA
Clark and Seipke (2023)
reviewed the limited DNA evidence. In a paper on Buteo phylogeny, Riesing
et al. (2003) used two mitochondrial markers (nd6 gene and pseudo-control region (ΨCR) and sequenced two unicinctus
specimens and one harrisi. Their
ML tree shows the two South American as sister to the harrisi specimen.
Raposo do Amaral et al.
(2009) sequenced mtDNA and the nuclear intron Fib5 for three Parabuteo
specimens, one from Texas and two from South America. As with the Riesing tree, the two South
American clustered together as sister taxa to harrisi.
A quick analysis of Parabuteo
cytb sequences (the three from Raposo and Lerner et al. harrisi sequence),
using Blast, resulted in two clades – the two harrisi as sister taxa to
the two unicinctus (pers. obv.).
Recommendation:
The new morphological
data and existing DNA and behavioral data support elevation of the two
subspecies and the redefinition of the ranges of the species as follows:
• P. unicinctus - resident in much of lowland tropical and
subtropical non-Amazonian South America, including west of the Andes in Chile,
Peru, Ecuador.
• P. harrisi - resident from se. California,
east to central Texas and south throughout n. Mexico, then south along the
Pacific slope from w.-central Mexico to Costa Rica.
Although the current
range of harrisi is described as occurring in northwest South America south
to northwestern Peru, new information about the Basic II and III plumages of unicinctus
suggests that these South American sightings were probably juvenile unicinctus,
because observers unaware of these plumages would be unable to distinguish them
from juvenile Harris’s Hawk. Clark and Seipke (2023) also noted that
researchers in Ecuador have not seen Harris’s there.
Current range maps and
eBird sightings for P. unicinctus show geographic separation of South
American populations from Central and North American, with a gap in
distribution in Panama. This is
consistent with an interpretation of the ranges of P. harrisi and P. unicinctus
being geographically separated.
Literature Cited
Clark, W. S. and S. H.
Seipke. 2023. Taxonomic status of Bay-winged Hawk Parabuteo (unicinctus)
unicinctus and Harris’s Hawk P. (u.) harrisi, with documentation of
delayed plumage maturation in Bay-winged Hawk. Bull BOC 143(2):142-152.
Dwyer, J. F. and J. C.
Bednarz. 2020. Harris's Hawk (Parabuteo unicinctus), version 1.0.
In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology,
Ithaca, NY, USA. https://doi.org/10.2173/bow.hrshaw.01
Lerner,
H. R. L., Kolaver. C. K. & Mindell. D. P. 2008. Molecular phylogenetics of
the buteonine bird of prey (Accipitridae). Auk 125: 304–315.
Raposo do
Amaral, F. R., Sheldon, F. H., Gamauf, A., Haring, E., Riesing, M., Silveira,
L. F. & Wajntal, A. 2009. Patterns and processes of diversification in a
widespread and ecologically diverse group, the buteonine hawks (Aves,
Accipitridae). Mol. Phylogenetics & Evol. 53: 703‒715.
Carole S.
Griffiths, July 2023
Comments
from Areta:
“YES. The differences in plumages of juvenile and
definitive harrisi and unicinctus are striking, and have indeed been long recognized.
Although not new to me, it is good to see the evidence for basic II and basic
III plumages of unicinctus being published and called to the attention of the
ornithological community. It is a pity that the wing molt of the specimens used
to substantiate the claims of basic II and III unicinctus is not shown in
the paper and not accurately described, and that the specimens examined in
museums have not been properly listed with their corresponding molt. The fact
that no basic II or III plumages are shown in flight in the paper itself is rather
confusing, as unaware readers may be drawn to think that birds can be properly
aged by looking at the body aspect: yet as described in the text, proper aging
is performed by looking at wing molt (something that Clark and Seipke have
championed for a long time, to be sure). I find it surprising that no attempt
was made to characterize the vocalizations of the two taxa; someone should
explore this. The limited genetic data do not provide strong support for
species status of unicinctus and harrisi, and are
compatible with different possible scenarios. However, I think that the data
collectively tip the scale to consider
unicinctus as a separate
species from harrisi, and the
burden of proof should be inverted. On a personal note, I lament that the
authors did not "find" that Pearman & Areta (Field Guide to the
Birds of Argentina and Southwest Atlantic, 2020) have also provided accurate
illustration of unicinctus (juvenile and adult). To conclude, I
vote YES to the split of unicinctus from harrisi, although I think
that a much stronger case could have been built to support this treatment.”
Comments from Stiles: “YES, in the sense that although
the data supplied by Clark & Seipke leave some notable holes, it definitely
shifts the burden of proof onto those who would maintain both groups as
subspecies under unicinctus.”
Comments
solicited from Therese Catanach: “The
fact there is some shallow population structure in a widespread species
(especially one that undergoes limited or no seasonal movement in much of its
range) is unsurprising. However, level
of genetic differentiation between the two currently recognized subspecies of Parabuteo
unicinctus is well within the range expected for intraspecific
variation. For example, 4 cyt b samples
from Parabuteo leucorrhous are also publicly available. Two of these samples, ANSP 180970 (tissue #
ANSP 660) and ANSP 186050 (tissue # ANSP 5082) are both from Ecuador and yet
exhibit similar levels of genetic differentiation (0.47% divergent) as those
observed between North (including a new cytb sequence generated by Catanach et
al. 2023) and South American populations of Harris’s Hawk (which range between
0.46 and 0.58% divergence). This level
of divergence is low when compared to other hawk species, for example a
sampling of Red-tailed Hawks show divergence as high as 1.7% when comparing
specimens collected in the United States.
When comparing these p-distances to those calculated for sister species,
Parabuteo leucorrhous and Parabuteo unicinctus are over 6%
divergent. When looking across
Buteoninae as a whole (using the data from Catanach et al. 2023), the average
cytb divergence is 2.9% divergent between sister species. Only 6 sister species are lower than 1.4%
compared to the maximum of 0.58% exhibited within the Harris’s Hawk
samples. Of these sister species pairs,
the species status of most has fluctuated in the literature (e.g. Haliaeetus
sanfordi and H. leucogaster and several Old World Buzzard
taxa). In fact, only one, the Buteo
galapagoensis and swainsoni pair is only 0.18% divergent and has not
been widely questioned. However, these
two taxa are morphologically distinct enough that a sister relationship was not
suspected until sequencing data recovered this arrangement (Bollmer et al.
2006) making it a very different situation than the two morphologically similar
Harris’s Hawk subspecies.”
Bollmer,
JL, Kimball, RT, Whiteman, NK, Sarasola, JH, Parker, PG. 2005. Phylogeography
of the Galápagos hawk (Buteo galapagoensis): A recent arrival to the
Galápagos Islands. Molecular Phylogenetics and Evolution. 39 (1): 237–247.
Catanach,
TA, Halley, MR, and Pirro, S. 2023. Enigmas no longer: using Ultraconserved
Elements to place several unusual hawk taxa and address the non-monophyly of
the genus Accipiter (Accipitriformes: Accipitridae). bioRxiv
2023.07.13.548898; doi: https://doi.org/10.1101/2023.07.13.548898
Comments
from Zimmer:
“YES,
although I don’t consider it a slam-dunk.
I’m really not all that impressed by the meager genetic data, but the
sum of fairly obvious differences in both adult and juvenile plumages, the
differences in molt sequences and number of plumage cycles between the two, and
the ecological/behavioral differences, combined with the fact that the two were
not only historically treated as separate species, but also were often treated
as belonging to separate genera, makes me think that the burden of proof should
shift to those favoring maintaining the one-species treatment. I would second Nacho’s call for a vocal
analysis to strengthen the case – I suspect that vocalizations might prove
diagnostic.”
Comments from Lane: “YES. As others state, I think
the overall amount of evidence makes this split quite reasonable. I have long
noticed that North American and South American Parabuteo differ. Even
those on the Pacific coast of Peru didn't match North American birds, so I
never understood how they could be considered harrisi? The present study
explains all this satisfactorily to me.”
Comments from Del-Rio: “NO. Although the morphological
differences exist, I am afraid the molecular differences are not compelling
enough. I will keep my standard criteria here.”
Comments from Robbins: “NO. Clearly, genetic
data do not offer support for species recognition. Moreover, like Nacho, I have issues with how
the data were (or were not) presented. Likewise as Nacho pointed out, there should
have been an attempt to ascertain whether there are differences in
vocalizations. Whether differences in
juvenile plumage merit species recognition is an open question. I vote NO for species recognition until there
is a clearer and more detailed analyses of these two taxa.”
Comments from Brian Sullivan (voting for Remsen): “The
authors should be commended for bringing this interesting and vexing taxonomic
issue back into the light. In this case, there are clearly two taxa involved—I
completely agree! But how and where those taxa come into contact, whether they
interbreed, and what their respective ranges are, all require further study. I
don’t think the proposed distribution break in Panama is the simple and clean
delineation the authors suggest it to be—at least not based on the images I’ve
found below, which show Harris’s-like birds all the way south to Ecuador in
South America, and more mixed types in Lima down through Santiago. South of
there, based on a quick look at photos in ML, it seems like most are Bay-winged
types. Everything east of the Andes seems like Bay-winged types.
“Given that I only spent an hour perusing the Macaulay Library’s
collection of these taxa, it seems relatively easy to find exceptions to the
hard and fast rules outlined in the paper, such as:
“There are no valid
records of Harris’s Hawk in South America.”
https://macaulaylibrary.org/asset/217536651
https://macaulaylibrary.org/asset/427018861
https://macaulaylibrary.org/asset/481506641
https://macaulaylibrary.org/asset/116191271
https://macaulaylibrary.org/asset/328118561
“All adult harrisi have unmarked dark
undersides to the remiges”
https://macaulaylibrary.org/asset/121846531
“whereas all adult unicinctus have whitish primaries
with narrow dark bands and black tips on the outer ones, but many adult unicinctus
have whitish secondaries with narrow dark bands (Fig. 2a), though some have
darker secondaries with some narrow white bands”
“See the many examples above that would be unicinctus
based on this proposed split that have all-dark remiges like harrisi.
“All adult unicinctus have a broad darker
subterminal band on the secondaries”
https://macaulaylibrary.org/asset/559744391
https://macaulaylibrary.org/asset/559744351
“We found no specimens
or photographs exhibiting characters of both taxa.”
“See example from Lima above.
“For now, I vote ‘NO’ on this proposed split, as I believe further
study is warranted. It could be that two species are involved, but more
information about how they interact, especially north and west of the Andes,
seems essential.”
Comments from Claramunt: “NO. I
don’t see compelling evidence for this split. The new data on juvenile plumages
by Clark & Seipke is very interesting and important; they found that the
juvenile plumage of birds from South America is different from that of birds in
Central and North America. But what is lacking for resolving this problem is a
detailed individual-level analysis of the geographic variation of the relevant
traits. That analysis would clarify whether there are two species or just a
single species that exhibits geographic variation. Framing this problem as an
issue of counting differences between two well separated taxa can be
misleading.”
“The main problem is that birds from the Pacific side of Colombia,
Ecuador, and Peru, have been considered to be harrisi, not nominate unicinctus. Clark & Seipke try to
minimize this issue by implying a “mistake” in the recent literature:
‘Some authorities (e.g., Dickinson & Remsen 2013, Clements et al.
2022) have mistakenly listed Harris’s Hawk for north-west South America.’
“In reality, most previous avian taxonomist have assigned these
populations to harrisi based on the examination of specimens that
showed uniformly dark underparts like harrisi (e.g. Hellmayr and Conover 1949, also citing
Chapman, Blake 1977). Those harrisi-like
individuals found from Colombia to Peru can be seen also in the photos posted
by Brian Sullivan.
“Therefore, birds from the Pacific side of South America seem to
show a mix of harrisi and unicinctus characteristics, exactly what would be expected
for a widespread species that has been exchanging traits via gene flow.”
Comments from Jaramillo: “NO. There does
seem to be something here that requires further work to adequately describe the
situation. Are there two, or are there three populations? The latter has not
been evaluated, but it is likely. That third Pacific population, what is it? An
intermediate, or a different population altogether, a subspecies of harrisi?
What I can say is that this species is a common hawk of Chile’s central zone,
yet in the last decade or two it has become more common in the far north, where
it is assumed that the Peruvian population moved south. To my eye, those
northern birds do not look like the true unicinctus of the south. I have
not understood exactly how they look different, but the tendency is to look harrisi
like.
“Also, it is worth noting that there are multiple gaps in the
distribution of this species, not just the one in Panama. There is an isolated
group in Colombia/Venezuela. Then we have the Pacific group that stretches from
S Ecuador to (now) northernmost Chile. But it has been and still is largely
isolated from the unicinctus of the southern cone. That gap is
narrowing. To my untrained eye, the birds in Colombia/Venezuela are harrisi.
The map shown in the powerpoint is also not correct: there is no connection of unicinctus
to the Colombia/Venezuela population via the area east of the Andes -- there
are no Parabuteo there. The fact that we have intermediate looking
birds, at least 4 isolated populations, and lots of questions means there is
more work needed.”
Additional comments from Lane: “One thing that may be confounding the issue is the
presence of escaped uncinatus in coastal Peru thanks to escaped
falconers’ birds and efforts to use hawks as pest control in agricultural areas
along the coast (this per the attached paper and
pers. comm. from Fernando Angulo). This may be changing the dynamics of which
taxon is present at least in coastal Peru. So this bit of information may be
something that clouded the distributions of the two taxa along the Pacific
coast of Peru, and perhaps elsewhere. Whether the two forms interbreed or not
would be worthy of study. Perhaps the votes on this proposal should be
postponed until such a study is run?”
Additional comments from Stiles: “Given the
multiple problems with the data of Clark & Siepke and Brian and Alvaro's
comments in particular showing various points of ambiguity, I agree that more
detailed information, largely requiring more field studies, would be needed to
fully understand this interesting problem, so I will change my vote to NO.”
Comments from Bill Clark and S.
Seipke:
“Note that there were three committee members who positively for
this split. Two of the three committee members who yoted yes mentioned the
differences in immature plumages. However, none of the six committee members
who voted no of one mentions this major difference between these taxa: the
difference in the number of immature plumages. No other of the 320+ species
diurnal raptors differs in the number of immature plumages between or among
subspecies. Surely this has a genetic basis and should be a factor in the
taxonomic decision.
“Specific comments:
“Sullivan found some photos of Bay-winged Hawks from the west of
the Andes that have uniformly dark remiges. What he did not find were any
photos of juvenile harrisi from this region. No photos exist in the Macaulay library
from Colombia to Peru that are of juvenile harrisi. All in this photo collection and museum
specimens from this region are of juvenile and Basic II & III are unicinctus. There may well be a subspecies of unicinctus
from there in which the adults have dark remiges. However, the birds west of
the Andes are not harrisi, as there are no juveniles of that taxa there,
only juveniles and Basic II & III unicinctus.
“Claramunt states that the birds from west of the Andes are harrisi,
but there are no photos or specimens of juvenile harrisi from this
region. Only adults with dark undersides of their remiges. He mentioned the
lack of individual-level analysis of the geographic variation in the paper. He
is mistaken in that every juvenile specimen or photo from South America fits
the characters of juvenile unicinctus and, likewise, every juvenile
specimen and photo from Central America north fits the characters of harrisi,
and there is no overlap in these characters.
“Jaramillo offers little in taxonomic insight other than there may
be a separate taxon west of the Andes.
“Catanach and Del-Rio think that the level of genetic differences
is too low for species, but the genetic analyses done to date are few and
shallow. Again, why did they not discuss how two subspecies can have a
differing number of immature plumages?
“Robbins questions the differences in juvenile plumage of the two
taxa, when it has been clearly shown in Clark & Seipke (2023) that they
differ greatly. The reason we did not use vocalizations is discussed below
under Areta.
“Areta (a positive vote) Mentions that Clark & Seipke (2023)
do not show Basic II and Basic II unicinctus in flight; they do however,
refer to URLs in the paper pointing to flying immature unicinctus that
show this primary molt of both ages of immatures.
“Areta suggests that vocalizations should be compared. We did
listen to some and felt that they were too similar to use for differences.
Sister species can have the same call. For Example:
• Amur Falcon
https://xeno-canto.org/species/Falco-amurensis
• Red-footed Falcon
https://xeno-canto.org/species/Falco-vespertinus
“Their calls sound the same. See also the attached sonograms
below.
“In summary, we feel that the consideration of this proposed split
by some committee members was shallow and did not take into account the great
differences in annual plumage sequences between these taxa, as well as the
great differences in plumages, especially juveniles.
“David Mindell, noted raptor taxonomist, supports our arguments
above.”
Comments from Fernando Angulo:
“I have
a couple of comments regarding the proposal and the PowerPoint presentation.
“1.
Lima’s Parabuteo unicinctus is a population formed from escaped birds
that were used by falconers, including me. We got our birds at that time, from
local trade. I am referring to years 1990 approximately, until more or less
2000 (This stopped when there were available birds from captive breeding). I myself
have contributed with at least one escaped bird. Birds that were acquired on those
days were from unknown origin (sellers told us “From the north”, referring to
Piura or Tumbes, but we have no certainty of that). So, the Lima population is
formed from unknown subspecies of Parabuteo unicinctus, basically, from
birds of unknown origin.
“2.
Distribution in coastal Peru, as far as I know, has to be taken carefully. The Lima
population is from escaped birds, which are expanding north, west, and east
from the Lima city. Also, there is a native population (you can check Koepcke’s
Aves de Lima book, where she mentions “rarely seen on the coast and Andean
slopes”). Other coastal populations can be safely regarded as wild, such as in
the dry forest of Tumbes, Piura, and Lambayeque, for example. Here, part of the
problem is that with growing agriculture activities on what was desert on the
Peruvian coast, “bird control” using trained Parabuteo unicinctus has increased
a lot, especially in Lima, Ica, La Libertad, Lambayeque, and lower Piura. This
means that any Parabuteo unicinctus found on any of the coastal cities
has to be carefully evaluated, because there is a great chance of being escaped
from trained birds.
“3.
Trained birds currently come from breeding centers that are using Parabuteo
unicinctus captured or obtained from the Lima population, or not. The Lima Parabuteo
unicinctus population originated from birds of unknown origin, and the
captive breeding centers uses birds from unknown origin (it can be from injured
birds from Lima population x a wild bird confiscated from illegal trade, or any
of the imaginable possibilities), so the Parabuteo unicinctus used for
bird control, i.e. the ones likely to be found on coastal cities, can’t be
regarded as typical looking wild birds.
“4.
A problem I see, is that several pics from Peru on the Clark & Seipke power-point
are taken by Lee Jones. Lee was a veterinarian working at El Huayco some 5 or
more years ago. We cannot eliminate the possibility that the pics he took
belong to Lima Parabuteo unicinctus (not wild birds) that are simply,
from unknown/uncertain origin or identity. So, those pics can’t be used to
separate these two spp into sp. (slides 8 and 21). On slide 21, you can notice
infrastructure of El Huayco in the background.
“5. On the other hand, I can see
plenty of birds from Peru that look more closely to what they call harrisi,
and are supposed to be as south as Panama, according to their ppt. https://ebird.org/checklist/S93955615 https://ebird.org/checklist/S79099153, from Lima, Piura, and I guess a
thorough search will find more.”
Additional
comments by Claramunt:
[in response to Clark’s points]: "My point is
that there seems to be a discrepancy between adult plumages and juvenile plumages
in SA birds E of the Andes: the adult plumage matches harrisi, the
juvenile plumage matches unicinctus. Which one is correct? We don't
know. We can't just assume that the juvenile plumage is correct in indicating
affinities here. Maybe both are "correct" and these birds share
traits and genes with both North American and eastern S American birds."