Singular Birds of Maldonado. 45 



already begun to think seriously of the great prob- 

 lems to which he devoted his life in later years. 



Among the birds at Maldonado Darwin noticed 

 one resembling a starling, which had a peculiar habit 

 of sitting upon the backs of horses or cattle and 

 pluming its feathers. It was interesting to him for 

 another reason : Azara had ascribed to it the cuckoo- 

 like habit of depositing its eggs in the nests of other 

 birds. Darwin found that the same was true of the 

 South American ostrich, which laid its eggs in the 

 nests of others indiscriminately. 



Of all the singular birds seen here the Polyborus 

 clianiango was perhaps the most interesting. It was 

 a carrion feeder, and Darwin often saw several within 

 the ribs of the skeleton of a horse. They were ex- 

 tremely savage, pouncing upon dogs, seizing rabbits 

 as they came from their holes, and even tearing the 

 leather from the rigging of the ship in what appeared 

 mere destructiveness. One was seen to carry off a 

 heavy bolas, while another seized a large glazed hat 

 belonging to a sailor and bore it nearly a mile from 

 the ship ; a small compass in a red morocco case 

 shared the same fate, and was not recovered. 



As we have seen, Darwin found the mouth of the 

 Plata famous for its electrical disturbances, and in the 

 sand-banks here he discovered some curious evidences 

 of the frequency of the bolts. Protruding from the 

 sand heaps were numerous vitrified and siliceous tubes 

 formed as the lightning entered the loose sand. 

 The sand was continually being blown about by the 

 wind, thus exposing the tubes ; similar ones in other 

 places have been traced for thirty feet. 



