144 THE STORY OF BIRD-LIFE. 



single egg is often deposited on the leaf of 

 a cocoa-nut-palm in a position, one would 

 think, of great danger, but it swings in the 

 wind apparently without risk of being broken. 



The sociable weaver-birds {Philhataerus socliis) 

 of Africa furnish us with, 1 believe, the only 

 instance of a colony, all, as it were, under a 

 common roof. The colony seems to be origin- 

 ally founded by a single pair of birds, another 

 joins their nest to that of the first pair, then 

 a third, a fourth and so on, up to as many as 

 three hundred and twenty pairs sometimes. The 

 size of such a mass of nests is so great as to 

 cause it to be occasionally mistaken for a native 

 hut. At last, by the accumulated weight, the 

 branch gives way and the whole comes to the 

 ground. This generally happens during the 

 rainy season when the dry grass soaking up 

 the wet becomes too heavy to be borne longer. 



The ani or "black witch," one of the American 

 cuckoos, may also be considered as a colony- 

 breeding bird. The difference however between 

 it, and that of the weaver -bird just described, 

 lies in the fact that several females lay their eggs 

 in one and the same nest and bear the duties of 

 incubation between them. 



Colonies, such as these, are only possible where 

 the birds' mutual interests do not clash : where 

 there is enough food in the immediate neighbour- 

 hood for all, and some to spare. 



Colonies of fish-eating sea-birds for instance, 

 are possible, because the food-supply is almost 

 inexhaustible. Colonies of birds of prey are 

 as a rule impossible, because the food-supply is 



