74 BIRDS OF LA PLATA 



to wonder at their strange instinct, which in its 

 wasteful destructive character, so unlike the para- 

 sitical habit in other species, seems to strike a dis- 

 cordant note in the midst of the general harmony 

 of nature* 



MISTAKES AND IMPERFECTIONS OF THE PROCREANT 

 INSTINCT OF Molothms bonariensis 



1. The Cow-birds, as we have seen, frequently 

 waste their eggs by dropping them on the ground, 



2. They also occasionally lay in old forsaken nests* 

 This I have often observed, and to make very sure I 

 took several old nests and placed them in trees and 

 bushes, and found that eggs were laid in them. 



3. They also frequently lay in nests where incu- 

 bation has actually begun. When this happens the 

 Cow-bird's egg is lost if incubation is far advanced ; 

 but if the eggs have been sat on three or four days 

 only, then it has a good chance of being hatched and 

 the young bird reared along with its foster-brothers. 



4. One female often lays several eggs in the same 

 nest, instead of laying only one, as does, according to 

 Wilson, the Molothrw pecoris of North America. I 

 conclude that this is so from the fact that in cases 

 where the eggs of a species vary considerably in 

 form, size, and markings, each individual of the 

 species lays eggs precisely or nearly alike. So when 

 I find two, three, or four eggs of the Cow-bird in 

 one nest all alike in colour and other particulars, 

 and yet in half a hundred eggs from other nests 



