192 THE MIGRATION OF BIRDS 



will eventually have rounder and shorter wings than 

 their continental allies. 



In some genera of birds it is comparatively easy to 

 determine the geographical range from an examination of 

 the shape of the wing. In the genus Acrocephalus, or 

 reed- warblers, for example, A. turdoides is noticeable 

 for its very pointed wing. Its migrations extend from 

 South Sweden to the Transvaal. A. orientalis, again, 

 is scarcely distinguishable except in having a slightly less 

 pointed wing. Its migrations extend from Japan to 

 Borneo. A. stentoreus has a decidedly more rounded 

 wing, and the limits of its migrations are from Turkestan 

 to India; whilst A. syrinx has the roundest wing of all, 

 and appears to have become a resident in the island of 

 Ponape. In the smaller species of the genus the fact 

 is equally striking. The sharp- winged A. sckcenobtznus 

 ranges from the Arctic Circle to South Africa, whilst the 

 more rounded-winged A. dumetorwn and A. bczticatus have 

 very limited ranges. 



There is a considerable difference of opinion as to the 

 origin of migration, some ornithologists holding that the 

 original home of a species was its winter quarters ; others 

 supposing that before the instinct of migration was formed 

 the species was a resident in the district where it now 

 breeds. Both views have their difficulties ; but the pre- 

 ponderance of evidence seems to me to be largely on 

 the side of the latter theory. In turning over a box of 

 Transvaal skins, shot during the breeding season between 

 September and March, it seems impossible to come to 

 any other conclusion. Throwing aside the brilliant birds 

 of the district, we shall find, 'especially if the box comes 

 from Potchefstroom, a variety of reed-warblers and allied 

 birds, which speak of swamps abounding with insects, 

 where birds of this kind delight to breed and find 



