134 



Barrows on Birds of the Lo7ver Uruguay. [July 



times. In general habits it is precisely similar to M. ater, and 

 the eggs of the two birds are scarcely distinguishable. I am 

 inclined to think that the Argentine bird differs less from our own 

 in its parasitic habits than is generally supposed. Its great 

 abundance and the comparative openness of the country will in 

 great measure account for the larger number of eggs found as 

 well as for the numbers sometimes observed in single nests. The 

 largest number I ever found in any nest at one time is four, but 

 not very rarely twice that number is found, as witnessed by many 

 reliable observers. Of course this overdoes the matter so as to 

 compel the rightful owner to desert the nest, but I suspect our 

 own Cowbird would be no wiser under similar pressure. 



40. Molothrus rufo-axillaris Cass. — Much less common 

 than the preceding, and usually met with only in the woods or 

 close to them. Here little parties of ten or a dozen may be 

 found at any season. Although so common, I was not able to 

 satisfy myself by observation either that they did or did not build 

 nests for themselves or impose on other birds. I have frequently 

 seen them in small parties clambering about the bulky nests of dif- 

 ferent species of Synallaxis^ and occasionally, even entering such 

 nests as if they owned them ; but examination afterward never re- 

 vealed eggs of any kind in the nests, so that I was at a loss to 

 account for the proceeding. Twice I have found in the nests of 

 Zonotrichia pileata a good sized white egg (in one case spotted, 

 in the other immaculate) differing in size, shape, and color from 

 the average egg of M. bonariensis^ yet I am not ready to say 

 that these were not abnormal specimens laid b}^ that species. 

 As I have never seen the eggs of M. rufo-axillaris I can of 

 course draw no conclusions in that direction, but suspicion 

 naturally falls on any member of a disreputable famil}- who has 

 not proved an alibi. 



41. Agelaeus thilius {Jl/ol.). — Abundant in flocks through 

 the year, but the flocks seldom consist of more than fifty individ- 

 uals, oftener of only a dozen. Breeds in the marshes diu"ing 

 October and November, but rather sparingly ; probably the ma- 

 jority breed farther south. The male in spring has a low but 

 sweet and varied song. 



43. Xanthosomus flavus {Gm.). — During the first year 

 spent at Concepcion this species was not observed, but in Octo- 

 ber, 1880, it made its appearance in flocks and remained to 



