FROM AFRICA TO THE ARCTIC 193 



unlimited food. As a matter of fact most of these 

 birds do breed there, and, because the winter is so 

 mild, remain there all the year round. But mixed up 

 with these African types we shall find a fair sprinkling 

 of our own reed-warblers, who have gone down there to 

 avoid our cold winters. These birds are not breeding ; 

 they have migrated to the Transvaal to enjoy the 

 mosquitoes of the Potchefstroom swamps, and when 

 the Potchefstroom birds have finished breeding and begin 

 their six months rest from family cares, they will some 

 of them migrate to the Arctic regions of North Europe 

 to breed amongst the mosquitoes which swarm on the 

 river-banks on the outskirts of the tundra. We can 

 scarcely conceive it possible that these species were ever 

 resident birds in the Transvaal. It seems much more 

 rational to conclude that they were once resident birds 

 in the subarctic regions of Europe, and now by the 

 change in the winter temperature of their original home 

 have come to South Africa as migrants, apparently out 

 of season in regard to their breeding habits, to mix 

 amongst birds, many of whom are closely allied to, if 

 not congeneric with, themselves. The cause of migration 

 is. want of food, not want of warmth. The feathers of a 

 Siberian jay or a Lapp tit are proof against any cold. 



Admitting that the various species of birds that breed 

 in countless thousands in the Arctic regions were once 

 residents there in the days when the climate was much 

 warmer than it is now, we still find some difficulties to 

 explain. In the first place, the Mammoth age does not 

 appear to have been so very much warmer than the 

 present. It is said that the remains of the foliage of 

 conifers, such as now exist in Siberia, have been found 

 in the stomachs of frozen mammoths. In the second 

 place, the question may be fairly asked : How about the 



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