Proposal (523) to South American
Classification Committee
Split Gray Hawk (Buteo nitidus) into two species
NOTE:
The following proposal was submitted to and passed by the North American
Classification Committee and is posted here, with minor editing, with the
permission of the authors. This proposed
split only affects us indirectly in terms of classification by truncating the
range of B. nitidus, but it does
affect directly our English name usage (change to Gray-lined Hawk).
Description
of the problem:
Gray Hawk (Buteo
nitidus, hereafter B. n. nitidus)
was described by Latham (1790) as Falco
nitidus, based on a specimen from Cayenne, French Guiana. Subsequently, a new taxon based on a specimen
from Veracruz, Mexico, was described by Schlegel (1862) as Asturina plagiata (hereafter B.
n. plagiatus). Schlegel considered B. n. plagiatus a separate species from B. n. nitidus because it was larger, had
more robust tarsi and feet, and had a greater number of tail bands. In their review of North American birds,
Baird et al. (1874) concluded the two taxa were climatic races of the same species,
and this view has largely prevailed since (Bierregaard 1994, Ferguson-Lees and
Christie 2001, AOU 2010). However, not
all ornithologists agree with this treatment.
Miller and Griscom (1921), van Rossem (1930), and Sibley and Monroe
(1990) treated the taxa as distinct species.
Friedmann (1950), Stresemann and Amadon (1979), and the AOU (1983)
treated them as conspecific, but commented that the taxa might be full
species. Johnson and Peeters (1963), in
their detailed analysis of plumage variation of woodland hawks, concluded,
“striking differences between the [northern and southern] races [of Gray Hawk]
are obvious”. These authors noted that
the plumage discontinuity occurs coincident with a gap in the species’
distribution in Costa Rica, which is also described by Stiles and Skutch
(1989). Blake (1977) presented
measurement data for all recognized subspecies of Gray Hawk, but he did not
quantitatively analyze measurement differences between taxa; he treated them as
conspecific, but noted that many consider them separate species. Millsap (1986) and Riesing et al. (2003)
evaluated morphological and genetic differences between the two taxa,
respectively, and concluded that they differed markedly.
New
information:
Until recently there was no comprehensive published analysis
of plumage, measurement, and vocal data for the Gray Hawk on which to base a
decision regarding the species-level status of the two taxa (Banks et al.
2006). In a recent paper, Millsap et al
(2011) compared plumages, morphology, and vocalizations of B. n. nitidus and B. n.
plagiatus, and found that allopatric B.
n. nitidus and B. n. plagiatus
differ diagnosably at very high probability levels in all age and sex classes
across a range of plumage, measurement, and vocalization characters. Adjacent B.
n. nitidus and B. n. plagiatus
populations were entirely separable based on plumage, even where ranges of the
two taxa approach one another in Costa Rica.
Discriminant function analysis (DFA) using measurements of body and tail
pattern characters of 405 museum specimens resulted in correct classification
of > 98% of juveniles and adult males and 88% of adult females, and
DFA using alarm call measurements resulted in correct classification of 100% of
the vocalizations. These results
parallel findings by Riesing et al. (2003) that the mtDNA difference between
the two taxa is on the order of 9%.
In addition, we propose to change the distribution
description for B. plagiatus to
reflect regular occurrence in southern New Mexico in the breeding season, based
on Williams and Krueper (2008), and to reflect occurrence of B. nitidus to 1600 m elevation based on
Hilty (2003).
Recommendation:
Collectively, all lines of evidence strongly suggest that
the current conspecific treatment of B.
n. nitidus and B. n. plagiatus
does not accurately reflect the extent of differentiation between the two taxa. We
recommend they be considered two species as described below:
Buteo
plagiatus (Schlegel). Gray
Hawk.
Asturina plagiata Schlegel, 1862, Muséum d'Histoire Naturelle des Pays-Bas, Revue méthodique
et critique (Catalogue) des Collections déposées dans cet Établissement, livr.
1, No. 4 (Sept.), Astures,
p.1, note. (Veracruz, Mexico)
Habitat.—Gallery
Forest, Tropical Deciduous Forest, Tropical Lowland Evergreen Forest Edge,
River-edge Forest (0-1300 m; Tropical and Subtropical zones).
Distribution.—Resident from southern Arizona (rarely),
southern New Mexico (rarely), western (rarely) and southern Texas south through
Middle America (including the Bay Islands, off Honduras) to northwestern Costa
Rica (Gulf of Nicoya region).
Northernmost breeding populations in Arizona, New Mexico, and western
Texas are largely migratory southward in nonbreeding season.
Buteo
nitidus (Latham).
Gray-lined Hawk.
Falco nitidus Latham,
1790, Index Ornithol. 1: 41. Based on the “Plumbeous Falcon" Latham, Gen.
Synop. Birds (suppl.) 1: 37. (in Cayana = Cayenne.)
Habitat.—Gallery
Forest, Tropical Deciduous Forest, Tropical Lowland Evergreen Forest Edge,
River-edge Forest (0-1600 m; Tropical and Subtropical zones).
Distribution.—Resident from Costa Rica (except
northwest), Panama, Colombia, Venezuela, Tobago, Trinidad, and the Guianas
south, west of the Andes to western Ecuador and east of the Andes to northern
Argentina, Paraguay, and southern Brazil.
Literature
cited:
American Ornithologists’ Union. 1983.
Checklist of North American Birds.
6th ed. American Ornithologists’
Union, Washington, D.C.
American Ornithologists’ Union. [Online].
2010. Check-list of North
American Birds. American Ornithologists’
Union, Washington, D. C. <http://www.aou.org/checklist/index.php3>
(24 February 2010).
Baird, S. F., T. M. Brewer, and R.
Ridgway. 1874. A history of North American birds, Volume 3. Little Brown and
Company, Boston, MA.
Banks R. C., C. Cicero, J. L. Dunn, A. W. Kratter, P. C.
Rasmussen, J. V. Remsen Jr., J. D. Rising, and D. Stotz. 2006. Forty-seventh
supplement to the American Ornithologists' Union Check-list of North American
birds. Auk 123:926-36.
Bierregaard, R. O. 1994. Grey
Hawk. In J. del Hoyo, A.
Elliot, and J. Sargatal [eds.], Handbook of the Birds of the World, Volume
II. Lynx Edicions, Barcelona, Spain.
Blake, E. R. 1977. Manual of Neotropical
Birds. University of Chicago Press, Chicago, IL.
Ferguson-Lees, J., and D. A. Christie.
2001. Raptors of the World. Christopher Helm, London.
Friedmann, H. 1950. Birds of North and
Middle America. Falconiformes. U.S. National Museum Bulletin, no. 50, part 2.
Hilty, S. L. 2003. Birds of
Venezuela. Second Edition. Princeton University Press, Princeton,
NJ.
Johnson, N. K., and H. J. Peeters.
1963. The systematic position of certain hawks in the genus Buteo. Auk 80:417-446.
Latham, J. 1790. Supplement to the
general synopsis of birds. Leigh and Southeby, London.
Miller, W. D., and L. Griscom. 1921.
Description of proposed new birds from Central America, with notes on some
other little-known forms. American Museum Novitates, no. 25.
Millsap, B. A. 1986. Biosystematics of
the Gray Hawk, Buteo nitidus
(Latham). M. Sc. thesis, George Mason University, Fairfax, VA.
Millsap, B. A., S. H. Seipke, and W. S.
Clark. 2011. The Gray Hawk (Buteo nitidus) is two species.
Condor 113:326-339.
Riesing, M. J., L. Kruckenhauser, A.
Gamauf, and E. Haring. 2003. Molecular phylogeny of the genus Buteo (Aves: Accipitridae) based on
mitochondrial marker sequences. Molecular Phylogenetics and Evolution
27:328-342.
Schlegel, H. 1862. Asturinae. Muséum
d'Histoire Naturelle des Pays-Bas, Revue Méthodique et Critique des
Collections Déposées dans cet Établissement, vol. 2, monograph
6. Leyden, Netherlands.
Sibley, C.
G., and B. L. Monroe. 1990. Distribution and Taxonomy of Birds of the World.
Yale University Press, New Haven, CT.
Stiles, F. G., and A. F. Skutch. 1989.
A guide to the birds of Costa Rica. Comstock, Ithaca, NY.
Stresemann, E., and D. Amadon. 1979.
Falconiformes. In E. Mayr and G. W. Cottrell [eds.], Checklist of birds of the
World, volume 1. Museum of Comparative
Zoology.
van Rossem, A. J. 1930.
A northwestern race of the Mexican Goshawk. Condor 32:303-304.
Williams, S. O. III, and D.
Krueper. 2008. The changing status of the Gray Hawk in New
Mexico and adjacent areas. Western Birds
39:202-208.
Brian A.
Millsap, Sergio H. Seipke, and William S. Clark, May 2012
Comments
from Stiles: “”YES, in the sense that
our birds become Gray-lined Hawk (thereby endorsing the decision to split,
which is the province of NACC).”
Comments from Pacheco: “YES. Endorsed for the good reasons
given in the proposal.”
Comments
from Robbins: “YES, long overdue to
recognize these as separate species. Gray-lined is an appropriate English name.”
Comments
from Jaramillo: “YES –
I am ok with the English name Gray-lined Hawk, although it is cumbersome. It
does have history though, so let’s keep it.”