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

384 BULLETIN 133, UNITED STATES NATIONAL MUSEUM
full molt SO that two have lost all of the rectrices. Young birds in
Juvenal plumage are similar to females but are streaked with whitish
below. A skin in this stage from Mendoza is much browner both
above and below than one from eastern Uruguay.
The naturalist from North America finds little in the habits and
appearance of the shining cowbird that is not reminiscent of
Molothrus ater of his native continent. Molothims h. honarien-ns
was found in small flocks during the most of the year, the largest
bands being noted in fall when at times several hundred flocked
together to feed in fields of ripened corn. Bands of from 20 to 50
frequented corrals and plazas at the larger ranches, and became so
familiar that they often walked about on dirt floors beneath the
porticos of the dwelling houses. At Las Palmas, Chaco, during cold
weather a little flock came about the fonda where I had living quar-
ters, but when it turned warm and pleasant for a day or two flew off
to less sheltered grounds. The birds fed in sociable groups on the
ground but at any alarm flew up suddenly to low perches in trees.
In pastures and fields these cowbirds gathered about grazing animals
and followed along in their company. They treated domestic stock
with the greatest familiarity. It was common on cold days to see a
little flock whirl into a yard and alight on the back of some horse
or ox which paid no attention to their coming. I have seen as many
as 15 birds resting on the back of one horse and have no doubt that
the warmth of its skin was grateful to its smaller companions who
seemed to find especial delight in burying their toes in the hair of its
back. Cowbirds were always attracted when grain was fed to horses.
They worked over sandy areas by scratching in the usual blackbird
fashion by jumping forward and then back, dragging their claws in
the dust on the return. In early morning flocks frequently resorted
to the open shores of lagoons to bathe. (PI. 20.)
The first indication of pairing was noted at the end of October
when three, taken on October 29 near Lavalle, Buenos Aires, were
all breeding; a female contained an egg nearly ready for the sliell.
At this period only small flocks were seen and it was not unusual to
find the birds in pairs. At Los Yngleses, the Gibson estate, I was
interested one morning in observing the maneuvers of a male cow-
bird about the newly completed nest of a Sisopygis icterophrys.
The female flycatcher was on the nest, as though brooding, though
in reality she was merely resting as her home was not yet completed.
The cowbird hopped about among the limbs approaching nearer and
nearer until the other bird finally darted out at him, though without
apparent animosity. The cowbird hopped up then to a point above
the nest, peered down into it for a few seconds, after which he flew
away apparently satisfied.