68 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



spiders found in the Hawaiian Islands; the few cryptozoic spiders 

 found there were introduced by man. 54 Flights of continental butter- 

 flies have often been carried by the wind to Helgoland and even to 

 England, Plusia gamma and Psilura monacha, for example. 55 



It is well known that birds are frequently transported by wind 

 storms. Sea birds are sometimes found far inland after storms; thus, 

 for example, petrels have been seen at Washington, and even beyond 

 the Alleghenies during a northeaster. 56 



The accumulated records of accidental occurrence of European 

 birds in North America north of Mexico, cited by the Check List of 

 North American Birds (1931), include 44 species. No less than 11 of 

 the 16 land birds in this list, however, have been recorded only from 

 Greenland, leaving five "accidentals" from Europe for the North 

 American continent. Examination of the best comparable list of 

 British birds 57 discloses records of 14 land birds of American origin, 

 and of 25 aquatic species. The British coast line is only about one- 

 tenth the length of the North American, and if this is taken into 

 account, the disproportion between the two lists becomes still greater. 

 This clearly exhibits the influence of the prevailing westerly winds of 

 the north Atlantic. 



Flowing water often serves as a means of distribution of terrestrial 

 animals. A number of Alpine species of snails have been brought 

 down to the plains and have established themselves on the river banks: 

 thus Pomatias maculatum on the Danube at Kehlheim and Helix 

 silvatica from western Switzerland to Karlsruhe and Worms. 58 The 

 woods bordering the La Plata have a fauna very different from that of 

 the neighboring pampas, especially snakes, amphibians, and brilliantly 

 colored insects of northern origin. 59 Large streams at flood time carry 

 driftwood, tree trunks, even whole floating islands, and thus transport 

 not only many small forms but a few large animals. The Paraguay 

 brings large snakes, crocodiles, and jaguars to the neighborhood of 

 Buenos Aires. 59 Spix and Martius report a number of monkeys on a 

 floating log in the Amazon, a squirrel on another, and a tiger cat and 

 a huge caiman on another. 



Branches and trees and large rafts are carried out to sea by the 

 rivers, and are then carried further by currents and winds. Masses of 

 driftwood and rafts up to a length of thirty meters have been observed 

 at the mouths of many tropical rivers, such as the Amazon, Congo, 

 Ganges, and the Indo-Chinese rivers. In the summer of 1892, a floating 

 island of about 1000 sq.m. extent was sighted repeatedly in the Gulf 

 Stream between latitude 39.5 and 45.5 N. and longitude 65-43 W.; 

 even large animals may be transported for long distances in this way. 



