Bulletin - United States National Museum - si-pddr - Smithsonian ...

BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 381
on June 29, 1920, the yelloAv-shoiildered blackbird was fairly common
in marshy spots near the Rio de la Plata in small flocks or scattered
singly throiif^h the rushes. On July 15 a flock of a dozen was noted
near a small lagoon at Las Palmas, Chaco, the farthest north at
which the birds were recorded. On October 21, near Dolores, Buenos
Aires, they were in pairs and males were singing. Near Lavalle
from October 23 to NoA'ember 15 they were common in the rush
grown cahadones. AVhere shrubs or low trees offered perches, the
males rested in them, though elsewhere they were content to cling
to the side of a reed.
Near General Roca, Rio Negro, from November 23 to December
3, a few were recorded mainly in irrigated alfalfa fields. At Carhue,
Buenos Aires, a pair was seen in a small marsh from December
15 to 18. On January 16, 1921, birds in molt were noted along tb'^
Arroyo Carrasco, east of Montevideo. At San Vicente, Uruguay,
flocks containing grown young were seen January 31, and at Lazcano,
Uruguay, small numbers were found in marshes grown with saw
grass from February 5 to 9. At Tunuj^an, ]\Iendoza, from ]March
22 to 28, they gathered with cowbirds in cornfields bordering the
cienagas where they did considerable damage to corn still in the
milk. There was a small but regular evening flight here to some roost
in the swamps south of town.
)
AGELAIUS CYANOPUS Vieillot
Agelaius cyanopus Vieillot, Nouv. Diet. Hist. Nat., vol. 34, 1819, p. 552.
( Paraguay.
The form here under discussion was fairly common in the Chaco,
but was not seen elsewhere. It was noted at Las Palmas, Chaco,
Riacho Pilaga,
July 22 to 31, 1920 (adult females, July 22 and 28) ;
Formosa, August 9 to IT (immature male and female, August IG) :
and Kilometer 80, west of Puerto Pinasco, Paraguay, September 10
(male). The wholly black adult males of this Agelaius were so
wary that none in that plumage were taken. A male shot August
16 in color is like the adult female but has a larger bill and longer
wing. The immature female is duller below than the adult of the
same sex. A male shot September 10 is in molt into adult feather as
black is appearing on the head and sides of the breast.
These blackbirds were found in marshy localities, near lagoons,
or about cornfields or other small cultivated tracts on low ground.
It was usual to see them resting on rush stems or walking about on
masses of vegetation that floated on shallow water. They were
frequently rather Avild, and when startled flew out in disorder with
undulating flight. Among growths of weeds on the ground they
walked about rapidly, clambering over considerable obstructions.
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