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106 BULLETIN 133, UNITED STATES NATIONAL MUSEUM
ROSTRHAMUS SOCIABILIS SOCIABILIS (Vieillot)
Herpetotheres sociaMlis Vieillot, Nouv. Diet. Hist. Nat., vol. IS, 1817,
p. 318. (Corrientes and Rio de la Plata.)
As the everglade kite from Florida, described by Ridgway®^ as
Eostrhamus sociahilis plumbeus^ may be distinguished from South
American specimens by the grayish wash on the upper surface, the
typical form will bear the trinomial designation used above.
Though Azara states that he had never seen his gabildn de estero
sociable in Paraguay, I found it about the lagoon at Kilometer 80,
west of Puerto Pinasco, on September 8 and 9, 1920, and noted many
little piles of empty snail shells at the bases of palm stubs, where
they had been carried and dropped when empty. The hawks were
shy, so that I had no shots at them. On the Estancia Los Yngleses,
near Lavalle, Buenos Aires, the everglade kite, known as the caracolero
was fairly common from October 28 to November 16. A
female in immature dress was taken October 28, and a male in the
same plumage, with one fully adult, on October 31. Apparently
the dark adult feathering is not assumed until the third year.
These hawks were found about open marshes often in little flocks,
that in one instance numbered as many as 11. When fence posts
were not available and there were no trees near at hand, the hawks
rested on the ground on very slight elevations or perched in the
rushes. At other times they soared in company in short circles,
often following this pastime for the space of nearly an hour. The
bluntly pointed wing, with its broad expanse and well-rounded out-
line, and sharply square-cut tail served to identify the species at
once, even when far distant. At this season they were somewhat
noisy and emitted a rasping chattering call that was audible at no
great distance, especially on days when the wind was strong. Near
their resting places I found piles of empty snail shells (in this case
of Amipullaria insularuTii d'Orbigny) where they had been discarded.
None of the shell heaps were extensive at this season and
I judged that the hawk was migratory and had only recently returned
from the north. In the Paraguayan Chaco, where the snail
hawks frequented marshy savannas, I saw them perched frequently
in the leafy tops of trees.
Near San Vicente, in eastern Uruguay, several everglade kites
were seen on January 31, 1921, near the Laguna Castillos, and one
was noted February 2 on a bahado bordering the Arroyo Sarandi
near the Paso Alamo. At Lazcano, Uruguay, they were seen over
saw grass marshes from February 5 to 7, and an immature female
was shot on February 7. At Rio Negro, Uruguay, they were ob-
** Baird, Brewer, and Ridgway, Hist. North American Birds, Land Birds, vol. 3,
1874, p. 209.