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 Molothrus 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 Molothrus 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 
