336 



C. SKOTTSBERG 



a general survey of the dispersal chances for other animals and also for plants. 

 The special instance cited (p. 197) is not very convincing. 



Birds are excellent flyers and thus capable of rapid and active spreading . . . capable 

 of crossing considerable stretches of open sea to settle in new territories. There is abun- 

 dant evidence of this, such as the resettlement of Krakatau Island, the recent arrival of 

 Australian birds in New Zealand, and the colonization of unquestionably oceanic islands. 



Not even the arrival of Australian birds in New Zealand brings conviction; 

 the colonization of "unquestionably oceanic islands" certainly does, if we can 

 prove it. Mayr continues p. 198: 



The possibility of transport by floats or in logs is not to be underestimated. Many 

 tropical currents have a speed of at least 2 knots, that is, about 50 miles a day, or 1000 

 miles in three weeks. It is probably not a great task for a wood-boring insect to survive 

 3 weeks in a drifting log. Air currents are, however, of uncomparably greater importance 

 than sea currents. Even slight winds are of great influence on the distribution of floating 

 and flying animals, as recent investigations have shown. It is astonishing how rich the 

 "aerial plankton" is, even up to altitudes of 1000 meters and more. Normal winds would, 

 of course, not account for the spreading of molluscs, flightless insects, and other small in- 

 vertebrates. However, most of the islands, with which we are concerned, are situated 

 within the zone of tropical hurricanes, the bfting force of which is quite extraordinary. . . . 



The fact that there are small molluscs and flightless insects on such typical oceanic 

 islands as Easter Island, Juan Fernandez and Saint Helena is almost unassailable proof 

 that such a method of dispersal is a reality. Tropical hurricanes carry for hundreds and 

 even thousands of miles. . . . The result of the recent surveys in the Hawaiian Islands, 

 the Marquesas, and on Samoa indicate that there are indeed very few animals that 

 cannot be transported across considerable stretches of the sea by winds, waves, other 

 animals or man. 



On p. 201 Mavr adds some general remarks: 



The means of dispersal of most plants and animals are much more extensive than 

 was formerly realized, and even rather irregular distributions can be explained without 

 the help of land bridges. Dispersal across the sea is, of course, most obvious for birds, 

 and ornithologists were among the first who accepted the ideas of the permanency of 

 continents and oceans. Most entomologists are also beginning to realize that they can 

 solve most of their distribution difficulties without land bridges. The conchologist, 

 however, postulates even today continental connections between all or nearly all the is- 

 lands where land shells exist. 



As we shall see below (p. 350) Mayr declared himself unable to explain how 

 land shells are dispersed. 



It seems that, also with regard to the birds, Mayr contradicts himself, for in 

 the same paper (p. 198) he asserts that most birds, particularly on tropical islands, 

 precisely the islands we are discussing, are extraordinarily sedentary, and as an 

 example he mentions that of 265 species known from that part of New Guinea 

 which is opposite New Britain, a distance of 45 miles, only 80 occur on New 

 Britain, and the situation in Western Papuan islands is even more conspicuous; 

 he mentions two islands only 2 miles apart, with rather different fauna. "Literally 

 hundreds of similar instances could be listed ... all of them indicating the sedentary 

 habits." One is likely to remember GuPPY's fruit-eating pigeons which were 

 thought to be responsible for the dissemination across the Pacific of seeds too 

 large for other birds. The "pigeons" are, now at least, restricted in range and of 



