190 U.S. NATIONAL MUSEUM BULLETIN 23 3 



infrequently, by utilizing deserted nests. In Salta, northwestern Ar- 

 gentina, Hoy (in litt.) also has noted eggs on the ground or in deserted 

 nests. As discussed more fully below (pp. 193-194), it may be noted 

 that late in the southern summer the year-old bu"ds tend to remain 

 in flocks and that individuals therein lay large numbers of eggs in size- 

 able nests which either have been aheady deserted or are quickly 

 abandoned as a result of the parasites' mass visitations. 



Careful reading of Hudson's statements conveys the impression 

 that finding scattered eggs on the ground was frequent in his experience 

 and that it was not restricted to the late summer months. In Hoy's 

 experience in Salta such evidence of wasted eggs chiefly was found 

 early in the breeding season. In other words, it was not restricted to 

 year-old, inexperienced birds. It is still somewhat puzzling to me, as 

 during six months that I spent in the field in Argentina, paying atten- 

 tion particularly to the cowbirds in areas where they were very numer- 

 ous, I never came across such a deserted egg. I do not doubt that 

 Hudson found many, but I can only wonder if this might have been 

 a local condition brought about by undue destruction of available nests 

 by weather or predators or by an undue numerical abundance of cow- 

 birds there. Furthermore, it is conceivable that Hudson may have 

 unwittingly multiplied his experiences in his memory, when writing 

 about them, by attaching too much inferential significance to a rela- 

 tively few such instances. At that time it was thought not improbable 

 that the cowbu'ds laid their eggs on the ground and then carried them 

 in their bills to the nests in which they were finally placed. This was 

 the current, although fallacious, assumption concerning the European 

 cuckoo, at that time the best known parasitic bird. There is no longer 

 any reason to assume that either cowbirds or cuckoos do this. 

 Actually, the only way in which it ever became known to Hudson that 

 the shiny cowbird did sometimes lay on the ground was the fact that 

 the eggs were left there and were not carried to a nest and that they 

 were found subsequently by him and his co-observers. 



We still know too little about the actual or the potential fecmidity 

 of the shiny cowbird to be able to estimate with any accuracy the per- 

 centage of its eggs that are wasted by depositing them either on the 

 ground or in abandoned nests. However, the waste is real, and it is 

 an element largely absent in the case of the brown-headed cowbird. 



Still another thought must be expressed in this connection. Ordi- 

 narily, cowbirds and, for that matter, parasitic birds in general, find 

 the nests they subsequently parasitize by watching the hosts build 

 them. There is even some reason to discern in this watching a stim- 

 ulus to ovulation. Therefore, depositing eggs on the ground or in old, 

 abandoned nests implies that this important directing and connecting 

 circumstance somehow is lacldng in these cases. This, in turn, 



