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

134 BULLETIN 133, UNITED STATES NATIONAL MUSEUM
differences other than those that serve to separate species. As there
are no structural characters known, either internal or external that
may be used to diagnose C hroicocephalus I prefer to include the
two species of hooded gulls treated in the present paper in the genus
Larus.
The call notes of the brown-hooded gull suggest those of Larus
franklini and are entirely different from the cawing calls of L. cir-
rocepJialus that was associated with it in small numbers. In the
Province of Buenos Aires maculipennis was common in late June,
1920, along the Rio de la Plata. Near Berazategui on June 29 these
birds were abundant in flocks that rested on the muddy beaches or
flew over the fields inland. Hunters decoyed them within range by
waving some white object and killed them in numbers for food.
From October 22 to November IT the brown-hooded gull was
common in eastern Buenos Aires in the vicinity of Lavalle. At this
season adults in full plumage Avere found in pairs that stood about
in the pampa near little pools of water or that came circling overhead
curiously with a scolding Kek Kek Kek to examine any in-
truder. At the same time I observed flocks of birds still in winter
plumage both on the open plains and along the sea beach below
Cape San Antonio. Apparently part at least of the young may
require two years to reach sexual maturit}^ and full plumage.
Occasional adult birds were observed with these flocks. The species
has a slow, flapping flight and with its short square tail, notes, and
general appearance is strongly suggestive of Franklin's gull.
I observed a dozen gulls near General Roca, Rio Negro, on
November 30, that may have been the present species. At Ingeniero
White, near Bahia Blanca, on December 13, brown-hooded gulls
were fairly common over the bay, and near Carhue, Buenos Aires,
they were found on the shores of Lake Epiquen. Near Montevideo,
Uruguay, in January the species was common.
Brown-hooded gulls breed in abundance on rocky islets along the
coast of the Department of Rocha, eastern Uruguay, and formerly
it was the practice to raid these colonies to secure (ggs in large
quantities. In recent years the commission charged with oversight
of agricultural affairs (the Defensa Agricola) has afforded the gulls
absolute protection, a step that has been well merited. Near La
Paloma, the seaport town for the city of Rocha, I saw bands of
these birds containing as many as 200 individuals feeding in the
pastures on the abundant grasshoppers. The gulls were gathered
in close flocks that flew slowly, barely above the earth, and as grasshoppers
were discovered dropped to earth to secure them. Those
from the rear rose continually to fly over their companions to the
head of the column so that the band drifted slowly along, as though
blown by the wind, in close though continually shifting formation.