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. 



