242 The World-Evidence. 



" The daily increase in the dimensions of the 

 young cow-bird was something immense, while his 

 younger companion seemed rather to diminish than 

 enlarge, and at the end of three days he died evi- 

 dently from want of food. 



Mr. Nuttall has seen the parent birds removing 

 the dead young to a distance from the nest and there 

 dropping them.* The inference is, of course, that 

 the intruders of their own eggs have killed the true 

 young of the nest, and left them for the parents to 

 remove from the nest. 



IV. In the case of Molothrus boiiaviensis the 

 males are much more numerous than the females. 

 " Azara says that nine birds out of ten are males. 

 The reason, perhaps, is that the male eggs of the 

 cow-bird are harder-shelled than the female eggs and 

 escape destruction oftener when the parent bird exer- 

 cises its disorderly and destructive habit of pecking 

 holes in all the eggs it finds in the nests to which it 

 intrudes. ... In Buenos Ayres, where they are 

 most numerous, they have a migration, which is only 

 partial, however. It is noticeable chiefly in the 

 autumn, and varies greatly in different years. In 

 some seasons it is very marked, when for many days 

 in February and March the birds are seen travelling 

 northwards, flock succeeding flock all day long, pass- 

 ing on with a swift, low and undulating flight, their 

 wings producing a sort of low, musical sound." f 



Major Bendire tells us in his excellent treatise on 

 the cow-birds in Smithsonian Report for 1893, ^^at of 

 the twelve species, three are found in the United 



* Baird's N. American Birds, ii, p. 155. 

 "l Birds of the Argentine, p. 73. 



