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

386 BULLETIN 133, UNITED STATES NATIONAL MUSEUM
tracheophone species have developed an unmarked egg, while others
who foist their product on oscines, whose eggshells in the main are
boldly marked, have maintained a heavily spotted egg. The parasitic
instinct among many of the cowbirds, however, seems poorly regulated,
so that at the present time many deposit in nests other than
those in which they should if their eggs are to have a maximum oId-
portunity to escape detection through their inconspicuousness.
In addition to the short list of parasitized species, recorded above,
I killed a juvenile cowbird that had a Poospiza persoTiata as foster
parent. A young bird secured at Tunuyan, Mendoza, had the side
of the mandible near the nostril greatly swollen, apparently from
the presence of a larval dipteran.
In an adult male M. h. honariensis the bill, tarsus, and feet were
black, the iris dull brown.
MOLOTHRUS BREVIROSTRIS (d'Orbigny and Lafresnaye)
Icterus brevirostris d'OsBiGNY and Lafresnaye, Mag. Zool., 1S38, cl.
2, p. 7. (Maldonado, Uruguay, and Corrientes, Argentina.)
The screaming cowbird, known with the common cowbird as tordo,
was local in distribution so that in Argentina the species was noted
in few localities. An adult female in old worn plumage was shot at
the Riacho Pilaga, Formosa, August 8, 1920, and on November 13,
near Lavalle, Buenos Aires, tAvo males were seen and one was taken.
In Uruguay the species was more widespread but was far from common.
At San Vicente one or two were seen in vacant lots within
the town limits on January 26 and 28, 1921, and near Lazcano several
were seen and three were taken in an area of open pastures on
February 8. A juvenile male was shot at Rio Negro, Uruguay, on
February 14, and another was recorded on February 17.
The notes of this cowbird were characteristic and entirely differ-
ent from those of the allied species. In February they were breed-
ing and males were markedly attentive to females. When flushed
it was usual for little flocks to alight on wire fences, when males
sidled over toward their mates with bowed heads and elevated neck
ruffs while they uttered a harsh note that may be rendered as
zhree-ah. Their general attitude at such times was reminiscent of
Tangavius aeneus. At times they uttered a sweetly whistled song.
Adult males were distinguished from the common cowbird even
when afield by the shorter, heavier bill, while in the hand they are
marked by blacker coloration and shorter tarsus. The adult female
is much blacker and the juvenile male darker than the corresponding
stages of bonariens-is. The young bird, however, is not easily sepa-
rated. In addition to the differences noted the present species seems
to have the base of the maxillar tomium heavier, and the rictus more
abruptly deflected than honariensis.