98 BIRD BEHAVIOUR 



birds in the Himalayas, that when he poisoned a 

 carcass with this drug, the Eagles which fed on 

 it were killed, but the Vultures flew away unharmed. 

 Tristram also records that when a pet Griffon 

 Vulture of his devoured the contents of a half- 

 pound pot of arsenical soap, the only result was a 

 violent fit of vomiting. It is not surprising, per- 

 haps, to find such endurance of virulent poisons 

 amongst Vultures, whose ordinary food consists of 

 putrid carrion, for it is well known that putrid or 

 sour food is very dangerous to most birds other 

 than carrion-feeders, even if they can be got to 

 eat it. 



Some substances are taken in by birds for reasons 

 that are at times hard to understand. The well- 

 known habit of grain-eaters and some omnivorous 

 forms, like Crows, of swallowing sand and gravel is 

 easily explicable, since these substances aid the 

 gizzard in comminuting the food ; but it is difficult 

 to see why Hawks, living on flesh, and casting up 

 indigestible substances, should need to swallow 

 gravel, which is shortly afterwards cast up again. 

 As the stones are worn away by natural abrasion in 

 the grain-eaters at all events, they are no doubt 

 useful in supplying mineral matter to the body, 

 just as the bits of shells and lime supplied to poultry 

 are useful in providing shell-forming matter for 

 the eggs. 



Some birds also eat earth ; a young Red-vented 

 Bulbul (Pycnonotus bengalensis) I kept in India 

 often did this, and I have seen a pair of an allied 



