GEOGRAPHIC DISTRIBUTION OF ANIMALS: OCEANIC ISLANDS 285 



Storms which reach hurricane intensity have great carrying power. Zim- 

 merman states that a wind of 75 miles per hour has a lifting force of 16 

 pounds per square foot and that hurricane winds may exceed twice that 

 velocity. The same author also recordsjiurricane action which tore large 

 she£t5_Di-iron rooting from a church on an island in Samoa and deposited— 

 it on another island 6 miles distant. We should not be surprised, therefore, 

 that large insecfsand birds may be carried great distances by winds. Insects 

 such as butterflies, grasshoppers, and beetles have been found as far as 

 1000 miles from their homes, and land birds are blown far out to sea. 

 Zimmerman records that a pair of North American kingfishers flew ashore 

 on Hawaii a few years ago. Many additional examples might be given, 

 serving to support the view that windstorms transport small objects for 

 long distances and blow flying animals far from the regions they normally 

 inhabit and to which, if undisturbed, they would confine their flights. 



A second means by which plants and flightless animals can reach oceanic 

 islands is through transportation by some animal capable of flight. Exam- 

 ples have been observed occasionally for many years, and the matter was 

 discussed by Darwin. Birds may carry mud and included small objects, 

 attached to their feet or feathers. Zimmerman records that a mallard duck 

 shot in the Sahara was found to have snail eggs on its feet. The same author 

 states that he picked a living bark beetle from the feathers of an owl. Seeds 

 may pass undamaged through the digestive tract of a bird. Accordingly, 

 migratory birds, or birds blown by storms from their normal ranges, may 

 account for occasional introductions of plants and animals on oceanic 

 islands. 



But neither winds nor migrating birds can aftord means of transportation 

 for such creatures as land mammals and reptiles. Although land mammals 

 are few on oceanic islands, such reptiles as lizards and geckos are common. 

 For larger land animals, therefore, some means of transportation across the 

 ocean itself must have been operative. Such means are aff'orded by natural 

 rafts and "floating islands." In times of flood large masses of earth and en- 

 twining vegetation, including trees, may be torn loose from the banks of riv- 

 ers and swept out to sea. Sometimes such masses are encountered floating 

 in the ocean out of sight of land, still lush and green, with palms 20 to 30 

 feet tall. It is entirely probable that land animals may be transported long 

 distances in this manner. Mayr (1940) recorded that many tropical ocean 

 currents have a speed of at least 2 knots; this would amount to 50 miles in a 

 day, 1000 miles in three weeks. Heyerdahrs (1950) balsa raft, the "Kon- 

 Tiki," carried six men from South America to a South Sea island, a distance 

 of 4300 nautical miles, in 101 days. This is an average of 42.5 miles per 



