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

BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 139
while the elongate tips of the outer tail feathers had been entirely
lost.
At Guamini, Buenos Aires, on March 7, 1921, I saw a flock of
10 slender, black-capped terns that seemed to be the present species,
but I did not approach near enough to them to secure specimens.
STERNA SUPERCILIARIS Vieillot
Sterna supcrciliaris Vieillot, Nouv. Diet. Hist. Nat., vol. 32, 1819, p. 176.
(Paraguay.)
This handsome little tern Avas seen first at Puerto Pinasco, Para-
guay, on September 3, 1920, when one was observed feeding along
an estero near the Paraguay River. On September 30 in the same
vicinity I encountered two that rested on dead stubs in the water or
circled about in the air. A carancho {Polyhoms p. hrasiliensis)
passed overhead and one of the terns pursued it for some time with
sharp metallic cries. A male in full adult plumage was tolled
within range by waving a hankerchief. On January 9, 1921, on
the beach near Carrasco, east of Montevideo, Uruguay, I encountered
two pairs of these small terns, evidently on their nesting grounds as
they darted constantly at my head with complaining cries until I
had passed beyond their bounds. On January 31 near San Vicente,
in the Department of Rocha, I found a dozen, all immature, beating
back and forth over the Laguna Castillos in company with Trudeau's
terns. Though young these birds were expert as fishermen, and were
so wary that I had difficulty in shooting one. The bill in this specimen,
a female, is not yet fully formed as it is only three-fourths as
long as that of adults. The bird is still in mottled juvenal plumage.
In habits and form this species is suggestive of the least tern and
frequents similar localities along large fresh-water streams or sea
beaches.
The adult male secured had the soft parts colored as follows: Bill
wax yellow ; tarsus and toes, olive ocher ; crus, yelloAvish olive ; claws,
black ; iris. Rood's brown. Measurements of this specimen are
Wing, 189; tail, 82; exposed culmen, 36.6; tarsus, 16.8 mm.
In a small series birds from Colombia and British Guiana seem
a trifle smaller than those from Paraguay.
THALASSEUS MAXIMUS MAXIMUS (Boddaert)
Sterna maxima Boddaert, Tabl. Plaucb. Enl. d'Hist. Nat., 1783, p. 58.
(Cayenne.)
On November 4, 1920, I shot a male royal tern on the beach 24
kilometers below Cape San Antonio, on the coast of the Province of
Buenos Aires. The bird was found in company with smaller terns.
November 15 several were noted in the mouth of Rio Ajo and in
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