CHAP. xx. REED-WARBLERS. 245 



the stories of swallows having been found hybernating in 

 caves and hollow trees, or of toads having been found in the 

 recesses of otherwise solid rocks. 



Many birds, such as the robin, the blackbird, the song- 

 thrush, &c., which are resident iu England, are migratory 

 in Germany. There is every probability that it is only 

 within comparatively recent times that these birds have 

 ceased to migrate in England, and we may fairly conjec- 

 ture that should the English climate remain long enough 

 favourable to the winter residence of these birds, they 

 will develop into local races, which 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 has a very pointed 

 wing. Its migrations extend from South Sweden to the 

 Transvaal. A. orientalis is scarcely distinguishable except 

 in having a slightly less pointed wing. Its migrations 

 extend from Japan to Borneo. A. stentorius 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. schoenoldenus ranges 

 from the Arctic Circle to South Africa, whilst the more 

 rounded-winged A. dumetorum and A. Issticatus have very 

 limited ranges. 



There is a considerable difference of opinion as to the 



