CH. IV] FLIGHTLESS BIRDS OF ISLANDS. 213 



others, there remains another series of facts of which a 

 brief epitome may be useful. It has been already pointed 

 out incidentally that many islands, whether oceanic or 

 not, are, or were until well within the historic period, 

 inhabited by birds not only of large size but also without 

 the power of flight, either owing to the partial abortion 

 of the wing muscles and bones or simply by use, like 

 the Weka rail of New Zealand. This is quite a common 

 characteristic of the birds of islands. The Dinornis of 

 New Zealand, the Dodo of Mauritius, the " Solitaire " of 

 Rodriguez, are instances to the point. It seems highly 

 probable that this large size coupled with an incapacity 

 for flight was correlated with the absence or at least the 

 rarity of fierce enemies ; mammalia are, if not absent, 

 small in those islands where these large and flightless 

 birds exist or existed. It is to be observed that even 

 among the Struthious birds, all of which are flightless, the 

 majority of the species are inhabitants of islands. This 

 majority is mainly formed it is true by the genera of 

 Dinornithida? ; but a large number of Cassowaries are 

 exclusively island forms. 



Birds are not the only animals which grow to a large 

 size upon islands. On a former page attention was called 

 to the huge tortoises of the Galapagos. These tortoises 

 are not altered apparently in any other respect ; they do 

 not for instance show any structural feature which could 

 be said to be analogous to the Sightlessness of so many of 

 the ornithic inhabitants of islands. But the tortoises of 

 the islands are actually the largest of the whole tribe ; 

 their unwieldy bulk, likely to be disadvantageous where 



