524 LAND ANIMALS 



The average human stature on Sardinia, 1619 mm., is smaller than the 

 average for Italy of 1645 mm. 



Insular forms are especially liable to extermination. Primitive ani- 

 mals, forms whose vitality has diminished and those which have be- 

 come modified as the result of the absence of enemies, are especially 

 exposed to destruction by introduced forms. The ant, Pheidole mega- 

 cephala, introduced in Hawaii, has destroyed the endemic forms in 

 extensive forest areas. Feral dogs and cats are exceedingly destructive 

 on islands where there were originally no predaceous mammals; the 

 toothed pigeon, Didunculus, of Samoa, has been forced to adopt ar- 

 boreal habits. The Lord Howe Islands were made a bird reservation 

 in 1879, but a plague of house rats has defeated the hope of preserv- 

 ing the endemic birds, 20 a plague which is not unknown in similar 

 islands. Fifty-nine species have become extinct in New Zealand in the 

 past 700 years, and there are 36 recently extinct forms known from 

 the Mascarene islands. 19 



Special insular climates. — The effect of insular climates on the 

 composition of their faunae remains to be considered. The relative 

 humidity is high, especially on small islands. The constant humidity of 

 islands, together with their great extent of coast line, favors the land 

 crustaceans, especially the amphipods and decapods. Most of the land- 

 inhabiting Orchestia (Amphipoda) occur on islands, 0. chevreuxi on the 

 Azores, 0. bottae on Cyprus, for example. Talitrus platycheles occurs 

 in the interior of Minorca ; other species of the same genus in Rodriguez 

 and in Tasmania. 27 Small tropical islands have great numbers of hermit 

 crabs and land crabs. On the Cocos Keeling islands there are no less 

 than 16 species of land crabs, and 7 hermit crabs which have adapted 

 themselves to land life. The cocoanut crab, Birgus latro, is widespread 

 in the Pacific islands. Many of these land crustaceans may range far 

 from the seacoast, and to the tops of mountains. 28 Hermit crabs may 

 adopt the shells of land snails (Bulimus, Helix) , as on Fernando Po 

 and in the Solomon Islands. 29 



Strong winds on small level islands subject the fauna to a severe 

 selection, for small animals which cannot escape them will be blown 

 into the sea. This factor especially affects insects and certain birds 

 with weak flight, and is the more effective the smaller the islands and 

 the more stormy the area in which they lie. 



Flightlessness, in general, is more frequent in insular insects than 

 in those on the continents (Fig. 131) . This has, however, been discussed 

 earlier (p. 396) . The small number of flying insects explains the absence 

 of insectivorous animals such as swallows, swifts, flycatchers, and in- 

 sectivorous bats. Thus there are only two bats in New Zealand, and 



