i86 ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



BIRDS (AVES) AS BROOD-PARASITES 



The Common Cuckoo (Cuculus canorus], as everyone knows, 

 deposits her just-laid egg in the nest of some small bird, carrying 

 it there in her bill. The proceedings of the young cuckoo, as 

 observed by Mrs. Blackburn, are thus described by Lloyd Morgan 

 (in Animal Behaviour]'. "One of the most remarkable instincts 

 of young birds is that of the cuckoo, which ejects eggs and nest- 

 lings from the home of its foster-parent.. Mrs. Hugh Blackburn 

 found a nest which contained two meadow -pipits' eggs, besides 

 that of a cuckoo. On a later visit the pipits were found to be 

 hatched, but not the cuckoo. At the next visit, which was after 

 an interval of forty-eight hours, * we found the young cuckoo alone 

 in the nest, and both the young pipits lying down the bank, about 

 ten inches from the margin of the nest, but quite lively after being 

 warmed in the hand. They were replaced in the nest beside the 

 cuckoo, which struggled about until it got its back under one of 

 them, when it climbed backwards directly up the open side of the 

 nest, and hitched the pipit from its back on to the edge. It then 

 stood quite upright on its legs, which were straddled wide apart, 

 with the claws firmly fixed half-way down the inside of the nest, 

 among the interlacing fibres of which the nest was woven, and, 

 stretching its wings apart and backwards, it elbowed the pipit 

 fairly over the margin, so far that its struggles took it down the 

 bank instead of back into the nest [fig. 1132]. As it was getting 

 late, and the cuckoo did not immediately set to work on the other 

 nestling, I replaced the ejected one and went home. On return- 

 ing next day, both nestlings were found dead and cold, out of the 

 nest ' (Birds from Moidart and Elsewhere]." Similar habits have 

 been described for the Cow- Birds (species of Molobrus] of America. 

 One species of these (M. rufaxillaris] actually lays its eggs in the 

 nest of a related species (M. badius\ which is industrious enough 

 to build one for itself. It may further be remarked in passing" 

 that some kinds of Cuckoo also construct nests, and bring up 

 their young in the usual way. 



Newton, after speaking of the social nesting-habits of certain 

 birds, makes the following suggestions as to the origin of brood- 

 parasitism (in A Dictionary of Birds]'. " In the strongest con- 

 trast to these amiable qualities is the parasitic nature of the 

 Cuckows of the Old World and the Cow- Birds of the New, but 



