134 A HISTORY OF BIRDS 



many other eggs appear to be carelessly dropped outside the 

 nest. According to another version, these eggs are arranged 

 in layers, with leaves between each layer, and are then aban- 

 doned, incubation taking place from the fermentation of the 

 decaying vegetable matter aided by the sun. 



Be this as it may it would seem that the Ani Cuckoos, like 

 their parasitic neighbours and relatives, owe the decadence of 

 their parental instincts to the fact that they are polyandrous, 

 and this because the males largely outnumber the females. 

 But for the fact that the parasitic types have succeeded in 

 producing eggs which, for the most part, are sufficiently like 

 those of their dupes to pass muster, they would have become 

 extinct. There seems to be no doubt about this mimicry of the 

 eggs — to which reference will be made again — and in this 

 connection it is of importance to note that the European 

 Cuckoo (Cuculus canorus) in India, chooses birds of European 

 types as its victims. 



That parasitism is due to polyandry— and to a less extent to 

 polygamy — we believe is almost certain. And this because 

 such a sexual relationship tends inevitably to lower the parental 

 instincts, just as monogamy tends to strengthen them. Among 

 the polygamous Game-birds there are not wanting signs of 

 degeneracy in the parental instinct. Thus the males commonly 

 leave the care of their offspring entirely to the female, which, 

 indeed, often have to guard them against the violence of the 

 paternal jealousy : while two females will frequently share a 

 common nest, a custom which offers an easy means of shelving 

 responsibility altogether, as in the case of parasitic species. 



