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114 BULLETIN 133, UNITED STATES NATIONAL MUSEUM
HETEROSPIZIAS MERIDIONALIS AUSTRALIS Swann
Heterospisias meridionalis australis Swann, Auk, vol. 38, 1921, p. 359.
(Laguna de Malima, Tucuman, Argentina.)
Swann recently has separated the southern hawks of this species
as above, on the basis of larger size and darker coloration. From the
specimens at hand it appears that this action may be sustained on the
basis of size, but that constant color differences correlated with geo-
graphic range, are not present. Nine specimens of tneridionalis
from Panama, Brazil (Para, Pernambuco, Diamantina, and Chapada),
show the following measurements: Wing, 378^17; tarsus,
90-111.5 mm. The series examined contains three females, one
doubtful male, and five birds without indication of sex. Three skins
from Argentina (Kilometer 182, Formosa, Corrientes, and Conchi-
tas, Buenos Aires) measure as follows: Wing, 423-450; tarsus, 109-
113 mm. Doctor Allen ^^ has described the plumage changes with
age in this species, findings that are verified in the series here at
hand. In general, birds during their first season are very dark
brown, almost black, save for more or less white on the under surface
and some rufous in the primaries and greater coverts. During the
second year the amount of rufous in the wings is increased and in-
vades more or less of the underwing surface as well as the lesser
wing coverts. In the third year the under parts and head become
rufous, barred below, save on the throat, with blackish, but the back
remains fuscous brown. In the fully adult plumage, apparently in
the fourth year, the upper back assumes an ashy shade, but otherwise
the bird is similar to what it was in the plumage of the preceding
year. Apparently the type of Swann's australis is a bird in third
year plumage. I am unable to detect any difference in color between
a bird in third-year stage from Para {meridionalis) ^ and one in a
similar plumage from near the city of Buenos Aires {australis).
An adult female (third year) that I secured on August 12, 1920, near
the Riacho Pilaga, Formosa (wing 423 mm.), is somewhat interme-
diate between the northern and southern forms, but has been identified
with the southern bird. A specimen in the United States National
Museum secured by Capt. T. J. Page at Corrientes (wing
448 mm.) seems to be typical australis. As Corrientes is just south
of the Paraguayan border it is not improbable that though merid-
ionalis was found in the Chaco at Puerto Pinasco, the form of eastern
Paraguay is the larger southern bird, in which case Swann's
name will become a synonym of Circus rufulus Vieillot,^^ based on
the gavildn acanelado of Azara.
This handsome hawk was first observed near Las Palmas, Chaco,
in July, 1920, but specimens were not secured until I entered the
wBull. Amer. Mus. Nat. Hist., vol. 5, 1893, pp. 145-146.
w Nouv. Diet. Hist. Nat., vol. 4, 1816, p. 466.