BIRD-NESTING IN ARGENTINA 369 



must be very great in order to make allowance for the in- 

 calculable numbers that are wasted, and still provide enough 

 to keep the ranks of the multitudes at their normal level. 



We did not find a single egg of M. b. bonariensis on the 

 ground, although Hudson states that in the vicinity of 

 Buenos Aires these birds "frequently waste their eggs by 

 dropping them on the ground." 



Dropping the eggs on the ground might entail a deliberate 

 waste, as we know of no reason why the bird should sup- 

 pose that they would be hatched and the young reared, 

 if scattered broadcast over the country. On the other hand, 

 this might merely indicate that the birds had found no suit- 

 able place in which to deposit their eggs. The form of waste 

 caused by the birds laying in old, disused nests, or by lay- 

 ing such a large number of eggs in a single nest that it is 

 impossible for the rightful owner to incubate them and 

 rear the young, can hardly be said to be deliberate, as it 

 is doubtless caused by a lack of intelligence; if the bird de- 

 signedly scatters its eggs broadcast on the ground, it is 

 wantonly wasteful; if it merely lays in disused nests, or 

 overcrowds nests actually occupied, the bird may simply 

 be stupid. 



It would be impossible to say what per cent of eggs laid 

 by this species of cowbird is wasted. Hudson estimates 

 that each female lays from sixty to one hundred eggs in a 

 single season, and it does not seem to me that this state- 

 ment is an exaggeration. One female which I dissected had 

 laid three eggs within the few preceding days, and a fourth 

 was almost ready to be deposited. 



The bird which suffers most from the parasitic habits of 

 the cowbird in the vicinity of Rosario de Lerma, is the 

 oven-bird {Fumarius rufus); however, of the great num- 

 ber of eggs laid in the nests of the above-named species, 

 our observations tend to show that the greater part 

 are lost. Among the scores of oven-bird nests which we 

 examined, only two were still occupied by the owners, the 

 desertion being apparently due to the invasion of the cow- 



