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 regu- 

 lated, 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 com- 

 mon. At San Vicente one or two were seen in vacant lots within 

 the town limits on January 26 and 28, 1921, and near Lazcano sev- 

 eral 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. 



