382 BRITISH BIRDS. 
in most, if not all, the true Cuckoos, the Bronze Cuckoos, and the Crested 
Cuckoos. The Ground-Cuckoos and the species belonging to other aber- 
rant genera all make nests and rear their own young, as do also the 
American Cuckoos ; but it is said (though on very doubtful authority) that 
some of the latter occasionally adopt the habit of our bird. The only 
other bird which is known with certainty to place its eggs in the nests of 
other birds is the American Cow-bird (Molothrus pecoris) , a species belonging 
to the American Orioles or Icterine, a subfamily of the Passeridz, con- 
necting the Starlings with the Finches. 
The cause of this curious habit is very difficult to discover. It has 
been suggested that the hereditary impulse to leave its breeding-grounds 
so early originally obliged it to abandon the education of its young to 
strangers ; but the same habit is found in many species in India and 
Africa, which are resident and do not migrate. Others have attributed it 
to the polygamous habits of the Cuckoo; but the Cuckoo is not poly- 
gamous, it is polyandrous. The males are much more numerous than the 
females. The sexes do not pair, even for the season. It is said that each 
male has his own feeding-grounds, and that each female visits in succession 
the half-dozen males who happen to reside in her neighbourhood. With 
the Cow-bird the case is said to be different. The males and females live 
indiscriminately in a flock together, and display neither sexual jealousy 
nor parental affection. A plausible explanation of the peculiar habits of 
the Cuckoo is to be found in the fact that its eggs are laid at intervals of 
several days, and not, as is usual, on successive days. Very satisfactory 
evidence has been collected (Bidwell, ‘ Zoologist, 1883, p. 372) that the 
Cuckoo lays five eggs in a season, and that they are laid at intervals of 
seven or eight days; but the American Cuckoo and many of the Owls 
very often do the same. This power has probably been gradually acquired 
by the Cuckoo so as to give the female time to find a suitable nest in 
which to deposit each egg. It is possible that this singular habit of the 
Cuckoo has arisen from its extraordinary voracity. The Cuckoo is a 
glutton; and the Cow-bird is said by American ornithologists to be 
insatiable in its appetite. The sexual instincts of the male Cuckoo appear 
to be entirely subordinated to his greed for food. He jealously guards 
his feeding-grounds, and is prepared to do battle with any other male that 
invades them, but he appears to be a stranger to sexual jealousy. He is 
said to be so absorbed in his gluttony that he neglects the females, who 
are obliged to wander in search of birds of the opposite sex, and appear to 
have some difficulty in obtaining the fertilization of their ovaries. The 
sexual organs of the male are probably so weak that the females are obliged 
to resort to several males before the complement of eggs is laid. The 
female in this species being thus the prepotent sex, the result, according 
to a recognized law of nature, is an excess of males in the offspring. The 
