12 THE DURATION OF LIFE. [I. 



was heard in the same forest for thirty-two consecutive years. 

 Birds of prey, and birds which hve in marshy districts, be- 

 come much older, for they outhve more than one generation 

 of men. 



Schinz mentions a bearded vulture which was seen sitting on 

 a rock upon a glacier near Grindelwald, and the oldest men in 

 Grindelwald had, when boys, seen the same bird sitting on the 

 same rock. A white-headed vulture in the Schonbrunn Zoo- 

 logical Gardens had been in captivity for ii8 years, and many 

 examples are known of eagles and falcons reaching an age of 

 over ICO years. Finally, we must not forget Humboldt's^ Atur 

 parrot from the Orinoco, concerning which the Indians said 

 that it could not be understood because it spoke the language 

 of an extinct tribe. 



It is therefore necessary to ask how far we can show that 

 such long lives are really the shortest which are possible under 

 the circumstances. 



Two factors must here be taken into consideration ; first, that 

 the young of birds are greatly exposed to destructive agencies ; 

 and, secondly, that the structure of a bird is adapted for flight 

 and therefore excludes the possibility of any great degree of 

 fertility. 



Many birds, like the stormy petrel, the diver, guillemot, and 

 other sea-birds, lay only a single ^gg^ and breed (as is usually 

 the case with birds) only once a 3'ear. Others, such as birds of 

 prey, pigeons, and humming-birds, lay two eggs, and it is only 

 those which fly badly, such as jungle fowls and pheasants, 

 which produce a number of eggs (about twenty), and the young 

 of these very species are especially exposed to those dangers 

 which more or less affect the offspring of all birds. Even the 

 eggs of our most powerful native bird of prey, the golden eagle, 

 which all animals fear, and of which the eyrie, perched on a 

 rocky height, is beyond the reach of any enemies, are very 

 frequently destroyed by late frosts or snow in spring, and, at 

 the end of the year in winter, the young birds encounter the 

 fiercest of foes, viz. hunger. In the majority of birds, the egg, 

 as soon as it is laid, becomes exposed to the attacks of enemies ; 

 martens and weasels, cats and owls, buzzards and crows are 

 all on the look out for it. At a later period the same enemies 



^ Humboldt's * Ansichten der Natur.* 



