Proposal (398) to South American Classification Committee
Re-split Buteo
poecilochrous from B. polyosoma
With this proposal I will present in more detail the
arguments for considering Buteo
poecilochrous a species distinct from
B. polyosoma, because I do not feel that the evidence was fully appreciated
in the preceding discussion of this question.
Part of the problem is that much of the relevant data were published in
Spanish in journals or publications not readily accessible to members of this
committee, and one of the key publications in English (Cabot & deVries
2003) in BBOC definitely suffered for want of a more firm editorial hand –
perhaps the reason Mark reacted so negatively to it (?). Moreover, a detailed
discussion of distribution and habitat selection of the two species, with
measurements of a smaller number of specimens, was published in BBOC (Cabot
1991) and merely cited but not discussed in detail by Farquhar (1998) in the
most substantive publication in favor of lumping them. However, these problems do not affect the
validity of the evidence itself.
The key piece of evidence advanced by Cabot &
deVries (2003, 2004) and not available to Farquhar was the detailed data on
complete plumage sequences of known-sex captive birds (sexed genetically as
well as morphometrically). Pavez (1998)
also published a detailed description of the plumage sequence of a captive
pale-morph B. polyosoma. These studies clearly established that both polyosoma and poecilochrous require up to six years to attain definitive
plumage. Cabot & deVries (2004) also
emphasized that both species have distinct pale and dark morphs, a fact
overlooked by Farquhar (1998) and earlier by Vaurie (1962) in a more
superficial study of plumages of these hawks.
The existence of pale and dark phases or morphs in the related B. albicaudatus has long been known,
although lack of detailed information on plumage sequences has led some (e.g.,
Johnsgard 1990) to suggest “continuous variation” between the extremes. Cabot and deVries found that even taking
individual variation into account, the plumage sequences of polyosoma and poecilochrous were specific to morph, age and sex in both
species. In general, the corresponding
plumages (age for age and sex for sex) in the pale morphs of the two are more
similar than in the dark morphs, but diagnostic differences are nonetheless
evident (Cabot & deVries, 2008 and in press). Complex age-related variations in coloration
had been mentioned (albeit not in such detail) for polyosoma by Goodall et al. (1951), Housse (1945), and Johnson
(1965); more detailed information for such changes were given for the related B. albicaudatus and B. (“Geranoaetus”) melanoleucus by Lehmann (1945) and
Torres-Barreto (1986). Farquhar (1998)
examined parts of the plumages separately but could not put together the whole
picture and did not consider feather replacement in individuals in any detail
but simply classified birds as “adults” vs. “juveniles”. The sequences documented by Cabot &
deVries clearly showed that Farquhar’s “age” criterion – type and extent of
tail barring – varies through several subdefinitive plumages according to sex,
such that no such simple division is meaningful.
Especially interesting was the discovery by Cabot
& deVries that males in subdefinitive plumage show a striking resemblance
to adult females. In effect, when
combined with morphometric data, Cabot & deVries could distinguish 48
different plumages (six per sex, thus 12 per color phase, thus 24 per species –
with the critical difference that each plumage was unequivocally related to
individuals of known sex and age. This
information permitted them to allocate each of the 400+ specimens examined to
species, sex, and age categories, as well as detecting geographic variation in
both species. In the process, they also
detected various misidentified and mis-sexed specimens (many of the older
collectors, as well as many museum workers, apparently sexed specimens by
plumage or used the now thoroughly discredited (by both Farquhar and Cabot
& deVries) wing formula of Stresemann to distinguish species). In some cases, specimens had even been
correctly sexed by the collectors and subsequently erroneously re-sexed by
others examining the skins later (see also Jiménez 1995). Faced with such a
diversity of plumages and lacking this key information, it is hardly surprising
that Farquhar ascribed plumage variability in these forms to random
variation. Moreover, I emphasize that
regardless of the details, this information negates his simple “adult-juvenile”
age classification.
Regarding the validity of such information, I note
that much of what we know about plumage sequences in large raptors (especially
tropical species) is due to observant falconers and less often, zoo-keepers:
only they have the opportunity to make continuous, close-range observations on
known individuals over many years.
Museum specimens are analogous to single isolated snapshots; banded
birds recaptured, to time-lapse photos of known individuals; but the data
advanced by Cabot & deVries are the equivalent of videotapes – and with
which would one prefer to document the exact sequence of events in, say, a
store robbery? Mark questioned the
provenance of the birds used by Cabot & deVries. These birds were taken from local nests in
Peru and Ecuador by falconers, and subsequently imported legally into the zoo
at Lima, where they are now reproducing in captivity under Cabot’s supervision,
such that they and their offspring can be studied further.
With respect to the morphometric analyses of Farquhar
and Cabot & DeVries, I have already noted that the oversimplified age
criterion of the former is bound to cause problems. Cabot & deVries found that some
measurements, especially wing and tail length, varied between age stages, (see
also Housse 1945, Jiménez 1995), as does the form of the primary tips (Vaurie
1962). They also detected geographic
variation in both polyosoma and poecilochrous. Birds from the southern portion of the range
of poecilochrous (Peru through
extreme northern Chile and Argentina) average smaller in a wide variety of
measurements and differ in various details of plumage; they recognize these as
a new subspecies fjeldsaai (Cabot
& deVries, submitted). On the other
hand, the southernmost populations of polyosoma,
beyond the range of poecilochrous,
are composed of larger individuals to the extent that subspecific distinction
could be warranted (Cabot & deVries, submitted). A further complication is that the lowland
birds of the Tumbesian region of SW Ecuador and extreme NW Peru (subspecies peruviensis) are smaller than highland
birds in the same latitudes and apparently are separated by altitude (no known
overlap). There are also island
populations of polyosoma in the
Malvinas (= Falklands) and the Juan Fernandez Islands; the latter in particular
is considered a distinct subspecies exsul
that might even warrant species status, as pointed out by Farquhar (1998). Raty has already noted that Farquhar’s use of
residuals is based upon the assumption that each form varies in the same manner
with respect to geography (longitude and altitude), age and sex; the data of
Cabot & deVries conclusively demonstrate that this assumption is
invalid. By lumping together all
individuals of both forms into “adults” vs. “juveniles” of each sex (likely
including mis-sexed and possibly misidentified birds) over the entire range of
this complex in his analysis, Farquhar could scarcely fail to produce a picture
of clinal variation suggesting conspecificity, especially given the overlap in
overall size between measurements of male poecilochrous
and female polyosoma. It would be desirable to repeat the analyses
of Farquhar using refined sex and age criteria, taking geographic variation
into account. For the present, the PCA
of Cabot & deVries, which used such criteria and demonstrated
nonoverlapping distributions in multivariate space, seems more satisfactory,
and to date they have encountered no intermediates between the two. The fact that most of the factors in their
analysis loaded most heavily on the first or “size” principal component simply
reflects the fact that sex for sex and age for age, poecilochrous is indeed the larger bird. Here again, it might be desirable to repeat
this analysis using more of the shape criteria they found, which would probably
increase the separation between these two forms.
Field observers with extensive experience of both
forms, including Cabot (1991), Koepcke (1994), Fjeldså & Krabbe (1990),
Walker (2002) and Pavez (2005), have noted that the “jizz” of the two forms
differs. This difference includes not
only the shape of the wingtip but also the width of the whole wing, including
especially lengths of the secondaries, a dimension not considered by Farquhar
(see Cabot 1991), the kind of flight (Pavez 2005), especially stationary flight
(Walker 2002); this information was dismissed by Farquhar. Also criticized by Farquhar were the
differences in behavior and ecology cited by Cabot & deVries, which he
considered were more likely due simply to adaptations to local habitats. This is likely true, but overlooks the fact
that in regions where they co-occur, polyosoma
and poecilochrous do indeed
occupy mostly distinct habitats – open grassy paramo and puna with many cliffs
for the latter, more xeric, brushy to wooded habitats for the former – but with
polyosoma also occupying more open and higher-elevation habitats both north and
south of the range of poecilochrous. In this context, it is worth noting that
the “southern cone perspective” supplied by Alvaro may not bear directly upon
the question of the specific distinction, because only polyosoma occurs in most of this region, occupying the entire range
of elevations, and the larger size of southern individuals of this species has
already been noted by Cabot & deVries.
Other Chilean workers with experience of both forms accept the validity
of poecilochrous as a species (e. g,
Jaksic & Jiménez 1990, Jaksic et al. 1991).
Of particular interest here is the recent discovery of a population of poecilochrous breeding in the
Antofagasta region of northern Chile along river valleys with facing cliffs in
which gallery forest has been removed (thus producing the more open situations
with cliffs favored by this species); polyosoma
also occurs in the region but in a different habitat (Cabot et al., a &
b., submitted; see also Fjeldså & Krabbe 1990, Jiménez 1991, Buitrón-Jurado
et al. in press).
Farquhar found little difference in the one
‘territorial-alarm’ vocalization he analyzed, stating that the variation
between both forms was encompassed by that shown in the related B. albicaudatus. Whether this vocalization is critical to
species recognition is debatable; one could also argue that it might function
in exclusion of polyosoma by poecilochrous from its more specific
preferred habitats. Convergence (or in
this case, non-divergence?) of territorial vocalizations has been documented in
a number of related and probably competing species pairs where their
territories abut. Cabot & deVries
considered this analysis “trivial” and asserted that experienced field
observers could indeed distinguish two species on the basis of vocalizations
(see Fjeldså & Krabbe 1990, Walker 2002, Pavez 2005). Here, I consider the published evidence to be
weak on both sides of the fence: the vocalization analyzed by Farquhar might
not be the most appropriate for the question of specific distinction, but
detailed spectrographic analyses of a range of vocalizations of both forms is
lacking. DeVries and his students are
now actively recording both species, but for the present, I feel that published
evidence on vocalizations is simply inconclusive to resolve this question.
The genetic data are also debatable. Farquhar reported no difference between the
two forms in a 600 bp sequence of the cytochrome b gene, as reported by Reising
et al. (2003), and criticized Cabot & deVries for not considering this data
- a bit unfair, as this paper and that of Cabot & DeVries in BBOC were
published nearly simultaneously.
Incidentally, Cabot has recently confirmed this, as reported in Cabot et
al., in press and Buitron-Jurado et al., in press. However, Lerner et al. (2008) found genetic
support in the CR_1 control region for independent origins of polyosoma and poecilochrous from albicaudatus,
thus supporting their status as distinct species. Lack of divergence in cytochrome b sequences
need not automatically indicate conspecificity – this gene has little to do
with species recognition characters, and were speciation to have been quite
recent, there might not been time for accumulation of mutations – in effect, we
are in the realm of lightning strikes rather than molecular clocks (the widely
accepted value for this gene is 2% changes in sequence per million years). In fact, Cabot & deVries (2008)
postulated that speciation is indeed recent, probably since the latest glacial
maximum, associated with the retreat of glaciers making high-elevation habitat
available. Moreover, a probably
comparable case exists in the genus Buteo:
B. swainsoni and galapagoensis show identical cytochrome b sequences, but are
universally recognized as species based upon multiple morphological and
behavioral criteria (Hull et al. 2008).
I might also state a case in point from the Bogotá region – that of the
hummingbirds Coeligena bonapartei and
C. helianthea. These species differ strikingly in coloration
but are quite similar in morphometrics.
Studies by Cadena and others have demonstrated no differences in
cytochrome b sequences of these birds, which in fact act as distinct species in
the wild. In an area where I have been
observing regularly over the last 15 years, I have noted replacement of bonapartei by C. helianthea and have never observed or captured an individual with
intermediate characteristics. This
replacement probably reflects interspecific competition in the context of
forest succession, helianthea being
more associated with forest while bonapartei
occurs more often in successionally earlier matorral habitats. The fact that hybrids have been reported from
the period of the “Bogota” skin trade probably reflects the decimation of local
populations of both, resulting in a scarcity of conspecific mates during this
period – no hybrids have been reported in at least the last 80 years (a
situation found in many hummingbirds of the region) and rather indicates that
species distinctions have been reinforced rather than weakened with the end of
such intense persecution.
In conclusion, the poecilochrous-polyosoma situation is indeed very
complex – but once the underlying pattern has been deciphered, the “mess” can
be resolved. In this case, the
resolution involved extensive experience with wild and captive birds over many
years, as well as exhaustive examination of museum specimens. The documentation of phase-, sex-, and
age-specific plumage sequences in each species was a key ingredient in the
resolution of the problem, and this information was not available to
Farquhar. There is now a mounting
accumulation of field, museum and laboratory data consistent with species
status for poecilochrous,
increasingly published within South America.
I consider that even without conclusive vocal differences (data on vocalizations
are now being gathered), this evidence definitely tips the balance in favor of
recognizing poecilochrous as a
species distinct from polyosoma, and
urge the SACC to consider this evidence in more detail. In short, I recommend a YES on this proposal.
References:
Buitrón-Jurado, G., J. Cabot, & T.
deVries. (in press). Distribution of the Variable Buzzard (Buteo polyosoma)
in Ecuador. Actas I Congreso Internacional de Aves rapaces y Conservación,
Quito 1-5 de abril 2008, Simbioe-Pontificia Universidad
Católica de Ecuador.
Cabot, J. 1991. Distribution and
habitat selection of Buteo polyosoma
and B. poecilochrous in Bolivia and
neighbouring countries. Bulletin of the British Ornithologists’ Club 111:
199-209.
Cabot , J. & T. de Vries. 2003. Buteo polyosoma and B. poecilochrous are two distinct species. Bulletin of the British Ornithologists’ Club 123:190–207.
Cabot, J. & T. de Vries. 2004. Age-and-sex
differentiated plumages in the two colour morphs of the Variable Buzzard Buteo polyosoma: a case of delayed
maturation with subadult males disguised in definitive adult female plumage. Bulletin of the British Ornithologists’
Club 124: 272-285.
Cabot, J. & T. de Vries (in
press). Comments on plumage patterns of
Buteo poecilochrous and B. polyosoma depicted in some
ornithological guides. Actas I Congreso
Internacional de Aves rapaces y Conservación, Quito 1-5 de
abril 2008, Simbioe-Pontificia Universidad Católica de Ecuador.
Cabot, J. & T. de Vries. MS. A new subspecies of Buteo poecilochrous.
Cabot, J., T.
deVries & C. Márquez. (in press). Sobre la especiación de Geranoaetus melanoleucus y los Busardos de cola blanca. Actas I
Congreso Internacional de Aves Rapaces y Conservación. 1-5 de Abril 2008. Simbioe-Pontificia Universidad Católica de
Ecuador, Quito, Ecuador.
Cabot, J., S. Alvarado & T. deVries. MS.
First breeding and new distributional and altitudinal records for the
Gurney Buzzard Buteo poecilochrous in Chile.
Cabot, J., T. deVries & S. Alvarado. MS.
Preferencias espaciales de las rapaces en
un sector de la meseta precordillerana, desierto de Atacama, región de
Antofagasta.
DeVries, T. 1973. The Galapagos Hawk.
An eco-geographical study with specific reference to its systematic position.
PhD Thesis. Free University of Amsterdam.
Fjeldså, J. & Krabbe, N. 1990. Birds of the high Andes. Apollo Books, Svendborg, Denmark.
Goodall, J. D., A. W. Johnson & R.
A. Philippi. 1951. Las aves de Chile, su conocimiento y sus costumbres. Platt
Establecimientos Gráficos, Buenos Aires.
Housse, R. 1945 Aves de Chile en su clasificación moderna,
su vida y sus costumbres. Ediciones de la Universidad de Chile, Santiago.
Hull, J. M., S.
K. Wesley, J. L. Bollmer, R. T. Kimball, P. G. Parker, N. K. Whiteman
& B. E.Holly. 2008. On
the origin of the Galápagos hawk: an examination of phenotypic differentiation
and mitochondrial paraphyly. Biological Journal of the Linnean Society 95:779–789.
Jaksic,
F.M, Silva S., Márquez P. & Contreras, L.C. 1991. Food Habits of the Gurney
Buzzard in pre-Andean ranges and the high Andean Plateau of northernmost Chile. J. Raptor Res. 25: 116-119.
Jiménez, J. E. 1995. Historia
natural del Aguilucho Buteo polyosoma:
una revisión. El Hornero 14:1-9.
Jiménez, J. E.
& F. M. Jaksic . 1990. Diet of the
Gurney Buzzard in the puna of northernmost Chile. Wilson Bulletin 102:
344-346.
Johnsgard, P.
1990. Hawks, eagles & falcons of North America. Smithsonian Institution
Press, Washington, D. C.
Johnson, A.W.
1965. The birds of Chile and adjacent regions of Argentina, Bolivia and Perú.
Platt Establecimientos Gráficos S.A., Buenos Aires.
Koepcke,
M. 1964. Las aves del Departamento de
Lima. Museo “Javier Prado”, Lima.
Lehmann F. C.,
1945. Rapaces Colombianas. Subfamilia Buteoninae. Contribuciones al estudio de
la Fauna de Colombia. Revista de la Universidad del Cauca 6:73-124.
Lerner, H.R.L.,
M. C. Klaver & D. P. Mindell. 2008. Molecular phylogenetics of the
Buteonine birds of prey (Accipitridae).
Auk 125 :304-315.
Pavez, E.F.
1998. Observaciones sobre el patrón de coloración en machos y hembras de
aguilucho (Buteo polyosoma, Quoy y
Gaymard, 1924). Boletín Chileno de Ornitología 5: 21-23.
Pavez, E. F. 2004. Descripcion de las
aves rapaces chilenas. Pp: 29-103 in: Muñoz, A., J. Rau & F. Yáñez
Valenzuela (eds.). Aves Rapaces de Chile. Cea ediciones, Valdivia, Chile.
Reynolds, P.W. 1935. Notes on the Birds of Cape Horn. Ibis 13th series 5: 65-101.
Torres Barreto, A. 1986. Cetrería
Neotropical Colombiana, Manual de volatería experimental con rapaces
suramericanas. Instituto Colombiano de Cultura Hispánica, Bogotá.
Vaurie, C. 1962.
A systematic study of the Red-backed Hawks of South America. Condor 64:277-290.
Walker, B. 2002. Field Guide to the
birds of Machu Picchu, Peru. PROFONANPE- National Trust Fund for Natural
Protected Areas. Lima, Peru.
Gary
Stiles, May 2009
Comments
from William S. Clark, Sergio H. Seipke, & C. Craig Farquhar: “We read nothing in this proposal that changes our position on this
taxonomic question as stated in comments in favor of the merger of these taxa
in Proposal 317. We
offer specific comments in rebuttal to the arguments presented in favor of this
proposal.
“First, all studies on
plumage sequences by age based on captive raptors are flawed. Raptors in
captivity do not molt the same as they do in the wild, unless they are flown in
falconry. WSC once saw a captive Bald Eagle
(Haliaeetus leucocephalus) that had gone through two molts, yet
it was still in juvenile plumage. Prout-Jones and Milstein (1986) flew captive
African Fish Eagles (Haliaeetus vocifer) and studied their molts and
plumages from juvenile to adult. Their results were the same as others on the
plumage sequence and time to adult plumage of four years. Southern (1964) also
proposed six years to adult plumage for Bald Eagle, again based on captive
eagles. But McCollough (1989) and Gerrard and Bortolotti (1988) found, as WSC
did from reading the band of an adult Bald Eagle, that they reach adult plumage
after four annual molts, or at about 4 ½ years old (Clark 2001). It is bizarre
to think of a buzzard taking six years to reach adult plumage. A much better
technique for determining the age classes of raptors that take more than one
year to reach adult plumage is to use the molt of the remiges (Miller 1941,
Clark 2004). WSC is studying White-tailed Hawk (Buteo albicaudatus), a
closely related buzzard, and from noting the remige molt he found that they
reach adult plumage in three years. Seipke (2007) established that the
Black-chested Buzzard-Eagle (Geranoaetus [Buteo?] melanoleucus),
another closely related species (but substantially larger-bodied than polyosoma-poecilochrous,
501-1280 g vs. 1700-3200 g; Dunning 2008), reaches Definitive Basic
plumage after four years. Again using primary molt, SHS is currently studying
the plumage sequence in Variable Hawk (B.
polyosoma) from over 140 museum
specimens in museums of South America and U.S.A., and he found that the species
reaches the Definitive Basic (adult) plumage in three years. There is no reason
to think that either of the taxa in question takes longer than three years to
reach maturity. WSC was fortunate to have looked at the large number of
specimens of the two taxa in question that CCF had amassed at the American
Museum of Natural History in New York. It was very obvious to us that there was
an almost complete overlap of plumages between them. All of the discussions in
this proposal and by Cabot and de Vries (2004) on ages and plumages are without
substance.
“Second, we strongly
disagree with the statement that any information or discussion in Lerner et al.
(2008) in any way suggests that these two taxa are separate species. On the
contrary, their DNA results, as those of Riesing et al. (2003) (cited but not
included in proposal references), strongly imply that the two are extremely
close, if not the same species. In
Lerner et al (2008) a Bayesian Posterior Probability of 1.00 leads to the nodes
for each grouping of polyosoma and poecilochrous, suggesting, again, extremely
close phylogenetic relationships. Stiles
(SACC #398) stated that, “Lerner et al. (2008) found genetic support in the
CR_1 control region for independent origins of polyosoma and poecilochrous
from albicaudatus.” However, CR-1 (mitochondrial pseudo-control
region) was not used in Lerner et al (2008); but data from that gene
were referred to from results in Riesing et al (2003). In the latter paper it was determined that an
average distance of 1.28% was found in the pseudo-control region (CR1) section
of a group consisting of Buteo polyosoma and B. poecilochrous. The conclusion was that these two should not
be considered separate species. In
short, there is no published work on the phylogenetics of these taxa that would
in any way support taxonomic distinction between B. polyosoma and B.
poecilochrous.
“Third, Stiles (SACC #398)
takes issue with the ‘debatable’ nature of Farquhar’s (1998) use of the
species-typical territorial/alarm calls in lending support for conspecificity
in polyosoma/poecilochrous. Those sounds
are likely the communications most likely under selection to influence
reproductive isolating mechanisms. Much
has been written in the scientific literature on this subject in other
species. While further data would be
useful, there is no evidence that those loud, long-distance calls could be used
to diagnose taxa, which is all that Farquhar (1998) meant to suggest).
“Fourth, we find issue with
the use of Cabot and de Vries (2003) result that discriminant function analysis
(DFA) supported distinct taxa because in that paper it was apparent that the
authors used a priori diagnostic criteria to place the birds into separate
groups which were then validated by the very statistical technique (DFA) used
to determine group membership; this is circular and erroneous for that technique. CCF (in prep.) re-analyzed data from Farquhar
(1998) using principal components analysis (PCA) on correlation matrices of
several morphometric variables (culmen chord, P8, P7, P6, tail, and tarsus),
separated by sex, and found a continuum along the major contributor to
explaining variation (e.g., P1; the ‘size’ vector) for the PCA score plot. Thus, taxonomic boundaries were not
discernable.
“Finally, as there is no way
to distinguish the two taxa for certain, they should be considered as one
species, unless and until someone comes up with a way to distinguish them. One
has to assume in light of their similarities that they would readily interbreed
should they come into contact. The problem is: how will we know when that will
happen? Or if it hasn’t already happened?
Besides, the ability to successfully interbreed is but one (basal) character
used to diagnose species.
“In summary, there is no
information in this proposal to counter the solid arguments for treating these
two taxa as the same species. We suggest the SACC reject proposal #398.
“Literature cited:
Cabot, J., and Tj.de Vries. 2003. Buteo polyosoma and Buteo poecilochrous are distinct species. Bulletin of the British
Ornithologists’ Club 123:190-207.
Cabot, J. & T. de Vries. 2004.
Age-and-sex differentiated plumages in the two colour morphs of the Variable
Buzzard Buteo polyosoma: a case of delayed maturation with subadult
males disguised in definitive adult female plumage. Bulletin of the British
Ornithologists’ Club 124: 272-285.
Clark, W. S. 2001. Aging Bald Eagles. Birding
33:18-28.
Clark, W. S. 2004. Wave
molt of the primaries of accipitrid raptors, and its use in ageing. Raptors Worldwide (eds. R. D.
Chancellor, and B.-U. Meyburgh) proceedings of the V World Conf. on Birds of
Prey, held in Budapest, Hungary, May 2003), World Working Group on Birds of
Prey, Berlin, Germany.
Dunning, J. B., Jr. 2008. CRC Handbook of
Avian Body Masses. Second Edition. CRC Press, Taylor & Francis Group, Boca
Raton, London, and New York.
Gerrard, J. M. and G. R. Bortolotti. 1988.
The Bald Eagle. Smithsonian Institution Press, Washington and London.
Lerner, H.R.L., M. C. Klaver & D. P.
Mindell. 2008. Molecular phylogenetics of the buteonine birds of prey
(Accipitridae). Auk 125:304-315.
McCollough, M. 1989. Molting sequence and
aging of Bald Eagles. Wilson Bulletin 101:1-10.
Miller, A. H. 1941. The significance of molt
centers among the secondary remiges in the Falconiformes. Condor 43:113-115.
Prout-Jones, D. V., and P. L. Milstein. 1986.
Sequential moult with age class establishment in the African Fish Eagle Haliaeetus
vocifer. S.-Afr. Tydskr. Natuurnav. 16:17-26.
Riesing,
M.J., Kruckenhauser, L., Gamauf, A., Haring, E. 2003. Molecular phylogeny of
the genus Buteo (Aves: Accipitridae) based on mitochondrial marker
sequences. Mol. Phylogenet. Evol. 27:328-342.
Seipke,
H. S. 2007. Aging Black-chested Buzzard-Eagle (Geranoaetus melanoleucus).
Pp. 220-228, in Bildstein, K. L., D. R. Barber, & A. Zimmerman
[eds.] Neotropical Raptors, Proceedings of the Second Neotropical Raptor
Conference, Iguazu, Argentina 2006.
Southern, W. E. 1964. Additional observations
on winter Bald Eagle populations: including remarks on biotelemetry techniques
and immature plumages. Wilson Bull. 45:121-137.”
Comments
from Dan Lane: “I find Gary's
comments in Proposal 398 interesting and, to a degree, persuasive, but I fear
that several important points have not been addressed with regard to the
nomenclature of the Buteo polyosoma/poecilochrous complex:
“The type specimen of poecilochrous (from
Yanayacu, Ecuador) reportedly (I believe this was mentioned in Farquhar 1998,
which I do not have before me at the moment [VAN:
PERHAPS YOU COULD CONFIRM THIS?]) does not show the primary formula
pattern that has been regularly attributed as "characteristic"
(indeed, it is widely touted as the primary [pardon the pun] field character
for identification!) of Puna Hawk. If this is true, then can we be certain that
the name is being applied to the proper taxon? Could it be that the name poecilochrous
is synonymous with "polyosoma" and the "Puna Hawk"
is actually not named? The holotype must be reviewed in detail in this respect.
“The name polyosoma belongs to birds on the
Falklands/Malvinas (there are other names available, albeit that they are
considered synonyms, from the South American mainland: erythronotus from
"Strait of Magellan", aethiops from "central provinces of
Chile" and peruvianus from "Eten, Lambayeque, Peru", all fide
Mayr and Cottrell 1979 [Peters' Checklist, Vol I]). It seems to me that an
important question that has yet to be addressed is whether or not mainland
birds and Falklands birds are best considered conspecific (or at the very least
monotypic) or not, since there are other very distinct taxa (many now
considered species) endemic to the Falklands.
“Finally, it seems to me that until a
well-supported molecular phylogeny (preferably including samples from near the
type localities of the various names) is performed among the various
populations within this complex to assess the presence of shared haplotypes or
lack thereof (and thus determining the relative relatedness of these
populations and the possibility of interbreeding between the Puna and
Red-backed groups), much of this discussion is academic at best...
“Proposal 398 does not address the three points
above, which are important ones with regard to what names should be applied to
what taxa. Should these points not be satisfactorily resolved in a publication,
I think it may be premature to make any new decisions regarding the status of
the two (?) forms.”
Comments
from Jaramillo:
“NO. I fear that this issue is becoming
the Neotropical equivalent of Larus
thayeri, perhaps a grey area where clarity is elusive and strong opinions
build on either side of the argument, partly due to the grey. I think thought
that we are moving in the right direction and after reading all of the Cabot
and deVries articles I was impressed by the picture they are painting, and the
way they are teasing out some interesting patterns in what at first seemed like
a random jumble of plumages. I am now convinced that there are two entities, or
at least leaning in that direction, while before I was well opposed to this
idea. But not all of this is new, I mean our Chile field guide is already many
years old and we illustrate three ages there, and note that younger males may
have reddish backs – so some of this has been known for a while. I will also
note that the presence of the second stage (what we called first basic in our
book), which are birds that are older than juveniles and have a barred tail
with a wider and darker subterminal tail band is an age group that we had not
noticed until Craig Farquhar brought it to our attention based on the work that
he had done on White-tailed Hawks where he saw this intermediate age group
earlier on. It may be a simplification, but it seems to me that after these two
age groups the birds become essentially adult like with added barring here and
there and it would not surprise me if in the field these hawks reach a terminal
plumage after three complete molts, or something like that rather than after 6
years which seems excessive to me. I don’t know if Farquhar included this
information in his choice of how to age birds for his paper by the way.
A few comments on the proposal:
“Other
Chilean workers with experience of both forms accept the validity of poecilochrous
as a species (e. g, Jaksic & Jiménez 1990, Jaksic et al. 1991).”
Note the dates of these papers -- this preceded the real controversy over these
taxa. At that point the authors were going with the status quo I would assume,
but I could be wrong.
“Of particular interest here
is the recent discovery of a population of poecilochrous breeding in the
Antofagasta region of northern Chile along river valleys with facing cliffs in
which gallery forest has been removed (thus producing the more open situations
with cliffs favored by this species); polyosoma also occurs in the
region but in a different habitat (Cabot et al., a & b., submitted; see
also Fjeldså & Krabbe 1990, Jiménez 1991, Buitrón-Jurado et al. in press).”
This is intriguing, but very confusing
biogeographically. For one, there never were gallery forests in that dry part
of Chile, bushes, maybe short trees yes, but no forest. So that is misleading,
this part of the world is very dry, and it never had anything that could be
called gallery forest, or at least the mental image of what a gallery forest is
to most readers. But these sites are lower elevation spots, yet farther north
in Putre the birds are polyosoma
(based on the plumage features Cabot and deVries are using in their papers),
and that site is at 3500m! At the latitude of Arica to Iquique, polyosoma reaches nearly to sea level in
some of the valleys, and in mid altitudes in places such as the pampa del
Tamarugal. Now why would these more highland specialist poecilochrous come down from the altiplano into the mid altitudes
just a bit farther south of this – I just find this odd. I would also want to
see exactly how they are identifying those birds in the field, just shape and
size, dark morph plumages – what exactly?
But really, those are nit-picks and I
apologize. The crux of the issue for me is that even accepting that there are
two entities, that they have different plumage types, and average different
size, and average different habitats and all that – what is the isolating
mechanism? In other words, could these not be subspecies? There is mention of
sympatry, but is there documentation of nesting of one type near a nest of the
other type? To me it seems that sympatry in the context of the Cabot and
deVries work is the presence of non-breeding polyosoma in the range of poecilochrous,
which is interesting, but not really what I am looking for. Plumage differences
are great to document, but in polymorphic species such as hawks it seems to me
that plumage is not really all that useful of an isolating mechanism. So what
are the displays, and the voices that keep these birds apart? This is the
missing bit now. Farquhar says voice is not different, but he had a tiny sample
size and perhaps we should be conservative and dump that bit of data, even so,
no one has data that says voices are different and consistently so. In hawks
that visually look alike and are sympatric (Accipiter
in North America to give an example), their voices are quite different, so if
these are two good biological species I would expect their voices to be
different too. But I need that data to accept that two species are involved.”
Comments
from Robbins:
“NO. Despite the lengthy exchange,
nothing has been presented that offers a definitive resolution. In fact, it appears that additional confusion
has been added to this mess. Given that
Clark et al. have ascertained that Buteo
albicaudatus and B. polyosoma
both reach definitive plumage in three years, one can’t help but question the
“six years to attain definitive plumage” statement about B. poecilochrous and polyosoma. The available genetic data demonstrate that
these two “taxa” (if poecilochrous is
even real) are extremely similar and that there may be nothing more than minor
population variation. The “jizz” comment
can be dismissed for a number of reasons, and Alvaro clarifies other
statements. Finally, Dan points out the same concerns that I expressed in
proposal 317 regarding the holotype of poecilochrous.
Given that there is little to
nothing to support species recognition at this point, I’m for subsuming poecilochrous within polyosoma.”
Comments
from Cadena:
“NO.
Interesting discussion, but I don't see anything really new and convincing to
justify changing my vote on proposal 317. The situation is very confusing, and
it seems that reaching a definitive decision on this case will be very
difficult in the long run. I think we are best served by having these taxa
lumped for now, if only for the sake of stability (how many times can we go
back and forth with little to no new data?). The beauty of the online SACC list
is all interested users of our classification can see all the complexities in
this group by reading our discussions on them.”
Comments
from Zimmer: “NO.
As was the case when we previously reviewed this issue, I am not
convinced by the arguments from either side.
Gary has done a fine job of reviewing this exceptionally complicated
case, and gives us reason to be skeptical of the methodology of the pro-lumping
camp. But, I am ultimately persuaded by Alvaro’s argument that vocalizations
and displays in these raptors are likely to carry more weight when it comes to
species-recognition and reproductive isolation.
Until we have that data, it seems we are expending a lot of time and
energy in sorting out something (minute differences in biometrics and plumage
sequences) that may have little bearing on whether these two populations treat
one-another as separate species. In the
absence of that data, I think it is better to hold off on changing our
species-limits yet again. And just let
me add that I, for one, am really glad that this is a taxonomic and field
identification problem that we don’t have to deal with in Brazil!”
Comments
from Stotz: “NO.
I agree with Alvaro that it is starting to look like there might really
be two taxa here, something of which I have never been convinced. However, I
don’t see how even if poecilochrous
and polyosoma are distinct taxa that
any of the data presented here suggest that treating them as distinct species
is currently the best option. As others have noted, in taxa that are so similar
morphologically, you’d really expect to see vocal differences. In the absence
of definitive evidence of vocal differences or clear sympatry without
intergradation I can’t see treating these as distinct species.”
Comments from Stiles:
“A
few additional comments with reference to those of Clark et al. First, the fact
that the complete sequence to definitive plumage in these hawks might take 3, 4
or 5 years is correct, and Cabot & DeVries acknowledge this – evidently the
difference, at least in males, may reflect the dominance status of the males in
multi-male breeding groups. However, the
very fact that this is a multi-year sequence disqualifies the simple
“juvenile-adult” dichotomy underlying Farquhar’s analysis – especially as a key
character he used, extent of tail barring, may take more than one plumage to
attain definitive and this differs between the sexes of both taxa. Much of the
rest of their arguments seem to be saying that if they could not distinguish
these two hawks, and did not detect any geographic variation in either, thus they
are perforce indistinguishable and invariable.
However, the evidence – published evidence – to the contrary is
mounting; I understand that the papers by C&D recognizing subspecies in
both taxa are now accepted for publication (or have been published?). Taking such geographic variation into account
effectively negates another major part of Farquhar’s argument for lumping
them.”
Comments from Nores:
“YES, pero no porque esté
convencido por lo que dice esta propuesta o por los comentarios que la apoyan.
Voto SI para volver a la situación
original o sea con las dos especies separadas. El hecho de que haya tanta
controversia en las opiniones indica que la situación no es nada clara y me
parece que SACC no puede eliminar una especie en base a situaciones como esta.
Considero ahora que para eliminar una especie los fundamentos tienen que ser
mucho más consistentes que para cualquier otro cambio. Alvaro dice que quisás
se trate de una buena subespecie pero no de una especie, pero los fundamentos
que da de lo que pasa en Chile y Argentina para mi indican que se trata de una
especie o variaciones de B. polyosoma,
pero no de una subespecie: “I have not looked into the specimens, but I doubt
that there are that many from these areas where lowland and highland
populations are entirely linked. In any case my field experience here is that
there is no break, no barrier, no clear difference between highland and lowland
birds”. En el análisis de Riesing et al. (2003) aparece B. poecilochrous separado de B.
polyosoma, pero ellos consideran que a nivel de subespecie. Pero si no son
subespecies, de acuerdo a lo expresado por Alvaro, serían especies.”
Comments from Remsen: “NO, but based
almost entirely on not wanting to reverse our earlier decision until the issue
is truly nailed convincingly one way or another. I now lean towards a two-species treatment
based on the additional new information, but given the volatility of the entire
situation and the existence of intriguing information on both sides, my view at
the moment is stick to the (most recent) classification until someone
demsonstrates that two species are involved by finding an isolating mechanism
between the two and evidence that they do not represent a single
intercommunicating gene pool along elevational gradients. That the two forms have a potential contact
zone thousands of km in length provides ample opportunity for someone to study
the situation directly in the field and to generate conclusive data one way or
another.”
Comments
from Pacheco:
“NO. Os argumentos apresentados pelos dois
lados que participam desta contenda não são menosprezáveis. Todavia, eu
mantenho o mesmo voto dado na Proposal #317 em decorrência, sobretudo,
dos resultados em Lerner et al. (2008) e Riesing et al. (2003).”