THE CLASS BIEDS. 337 



the soil, and deposit therein the egg or eggs to be hatched, 

 but with the greater number it is quite otherwise, and the 

 species may often be known by the form of the nest ( 328). 

 The warm and light substance, called eiderdown, used in 

 domestic economy, is the soft down which the bird pulls from 

 its breast to line the nest. 



The lay of eggs (ponte) takes place generally once a year, 

 sometimes twice ; but in a domestic state, the fecundity is 

 still greater. In the smaller species, the number of eggs 

 exceeds that of the larger ; the eagle lays but one or two ; the 

 tomtit and the raven, from fifteen to twenty. 



Fig. 325. Gypaetos, or the Lamb-slaying Vulture ; Bearded Vulture ; 

 Laemmergeyer. 



The constancy with which the parents sometimes the 

 female only, sometimes also the male hatch their eggs ; the 

 care they take of their young when they appear ; the courage 

 and intelligence shown by the parent bird in defending the 

 young, are facts within the observation of all. Nevertheless, 

 there are some birds, as the cuckoo, which deposit their egg 

 or eggs in the nests of other birds ; the young cuckoo gra- 

 dually dislodges his companions from the nest, and occupies 

 the whole. It afterwards rejoins its parents, which seem to 

 remain in the neighbourhood for that purpose. Instinct leads 

 the cuckoo to deposit its eggs in the nest of some insectivorous 

 bird (that being the food on which its own young requires to 

 be fed), such as the nests of the linnet, yellow-hammer, black- 

 bird, &c. 



Notwithstanding the strength of the instinct which leads 

 birds to hatch their eggs, it seems certain that it may be 

 z 



