SUCCESSIVE ARRIVALS OF DIFFERENT SPECIES. 341 



I believe every species keeps to its own particular elevation, 

 and that the atmosphere contains regular strata of birds of 

 prey, which, invisible to the human eye at these enormous 

 altitudes, are constantly resting upon their wide -spread wings 

 watching with telescopic sight the world beneath. At that 

 great elevation they are in an exceedingly cool temperature, 

 therefore they require no water; but some birds that make 

 long flights over arid deserts, such as the marabou stork, 

 and the bustard, are provided with water sacks: the former 

 in an external bag a little below the throat, and the latter 

 in an internal sack both of which contain a large supply. 



As the birds I have enumerated invariably appear at a 

 carcase in regular succession, I can only suggest that they 

 travel from different distances, or elevations. Thus the 

 marabou stork would be furthest from the earth. The large bare- 

 necked vulture would be the next below him ; followed by the 

 red-faced vulture, the buzzard, and the crow. That (the crow) 

 is generally about the surface. From their immense elevation, 

 birds of prey possess an extraordinary field of vision, and 

 although they are invisible from the earth, there can be no 

 doubt that they are perpetually hunting in circles within 

 sight of each other. Thus, should a bird discover some 

 object upon the earth, his sudden pounce would be at once 

 observed and imitated by every vulture in succession. His 

 rush would act like a telegraphic signal to others, which 

 would be rapidly communicated to every vulture at successive 

 airy stations. 



I have frequently watched these birds when I have shot 

 an animal, and my people have commenced skinning; but 

 not a bird has been in sight as I have lain upon my back 

 and gazed into the spotless blue sky; but hardly has the 

 skin been half withdrawn when specks have appeared in the 

 heavens 'Caw, caw' has been heard from neighbouring 

 trees : the buzzards have swept down close to my people and 

 have snatched morsels of clotted blood from the ground. 

 The specks have increased to winged creatures, at that great 



