42 SECRETS OF ANIMAL LIFE 



at first sight. ( i ) To begin with, it is not an iso- 

 lated phenomenon. It occurs in many other cuckoos 

 and in the quite unrelated Cow-Birds. Some kinds 

 of Old World Cuckoo follow the usual routine of 

 nesting and brooding; the American Black-Billed 

 Cuckoo, though usually a normal nesting and brood- 

 ing parent, occasionally puts an egg in the nest of 

 another bird; at least one species of Oriental 

 Cuckoo is parasitic in one part of the country and 

 nests in another; and there are many instances of 

 diverse kinds of birds casually laying in the nests 

 of their neighbors. Thus the cuckoo's evasion of 

 the normal parental duties is not an isolated 

 phenomenon, and it is also instructive to remember 

 that the parasitic instinct is not always perfect. 

 Many cases are known of a cuckoo's egg in an 

 altogether unsuitable nest, for instance, in that of 

 a bird which does not feed its young on insects. 

 (2) A second consideration is that the mother- 

 cuckoo's behavior is congruent with some other 

 peculiarities in the bird's constitution and ways. 

 Thus there are far more males than females (some- 

 times perhaps five to one), and polyandry is the 

 natural result, as has happened also with the Cow- 

 Birds. And while it is probably going too far 

 to call the polyandry the cause of the parasitism, 

 it will tend to a slackening of parental ties, and in 

 any case the parasitism is adapted to the polyandry. 

 Similarly, the great fertility of the cuckoo (some- 

 times credited with a score of eggs, though a dozen 

 is probably nearer the truth) is as likely to have 



