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

BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 135
Such flocks were a usual sight and to their activities may be at-
tributed the comparative freedom of this region from the plagues
of locusts that are frequently so destructive elsewhere. The useful
habits of these gulls are recognized by many farmers, who object to
hunters who kill the birds, an attitude that may be followed with
great advantage in other regions.
Xear San Vicente on January 31 I found brown-headed gulls common
near the Laguna Castillos where I saw several individuals sick
or dead from alkali poisoning. This gull was common near the
large lakes at Guamini, Buenos Aires, from March 3 to 8, and was
observed in abundance in the marshy region below Cafiuelas. At
this season adult birds were ragged and disreputable as they were
in molt. In the majority the body was clothed in winter plumage,
but wing and tail feathers, more notably the outer primaries, were
still in process of renewal. Adult and immature individuals, gath-
ered along the lake shore in flocks that contained as high as 100
individuals, were wary as they were shot by hunters at every op-
portunity. A thousand birds or more were seen daily. Flocks fre-
quently passed out to feed in the pastures and were observed following
plowmen at work in the fields to feed in the freshly turned
furrows.
No gulls were observed during my work in the Chaco.
This species is known in Argentina simply as gaviota.
LARUS CIRROCEPHALUS Vieillot
Larus cirrocephahis Vieillot, Nouv. Diet. Hist. Nat, vol. 21, 1S18, p. 502.
(Brazil.)
The gray-hooded gull was observed only at the Estancia Los
Yngleses, near Lavalle, Buenos Aires, from November 1 to 10, 1920,
and at the mouth of the Rio Ajo in the same vicinity on November
15. An adult female was taken November 1, and an adult male,
preserved as a skeleton, on November 10. After minute comparison
of four of these gulls from Buenos Aires, with a series of 27 from
Africa, all adult, I may only substantiate the observations of others
and state that, anomalous as it may seem, there is no apparent difference
between birds from the two localities. Those from South
America seem very slightly larger but in the series at hand the
distinction is too slight to be reliable. One may well ponder on
the conditions that have brought about such a remarkable distribution
in this species and on the length of time that the two
groups of individuals have been separated.
The adult bird is easily distinguished from the brown-hooded gull
that inhabits the same region by the much lighter head, a difference
that may be detected in a favorable light at a considerable distance.
The note of cirrocephalus is a strange caw caw, similar to that of a