RAXGE BASE OR REFUGE AREAS 45 



The Cape Verd Islands are a much more debatable 

 area. They are probably oceanic islands of great 

 antiquity, separated from continental Africa and from 

 themselves by a sea some 7000 feet in depth. They are 

 also extremely isolated, lying between 300 and 400 

 miles from the coast of Senegambia. Unfortunately, we 

 possess few reliable particulars respecting the fauna of 

 these islands. There can be little doubt that they have 

 been entirely populated by fortuitous emigration from 

 the Palaearctic and Ethiopian regions. There is certainly 

 a strongly-marked Palaearctic element in the avifauna, 

 combined with several Ethiopian forms, some of the 

 species very clearly indicating the line of emigration 

 followed. The islands are situated off the African coast, 

 a little to the south of the Sahara, and probably in a 

 direct or nearly direct line with the ancient southern 

 shore of that sea which once covered the Desert. Some 

 of the birds appear to have emigrated along the southern 

 coasts of this ancient sea, or, in more recent times, along 

 the borders of the Desert from more southern areas in 

 Africa. It is true one or two species of birds are found 

 in the latter islands as well as in the Cape Verds, but 

 there is nothing to suggest a southern emigration ; whilst 

 on the other hand we have absolute proof of a north- 

 western emigration from the south. Thus the Blackcap 

 Warbler {Sylvia atricapilld) is only known to resort to 

 the Canaries in autumn, when large numbers visit the 

 islands and swell the resident population of this species. 

 Now, did the birds pass further south by this route they 

 would be seen in spring coming north again, but no 

 such migration has been remarked. This Warbler passes 

 the Nile valley and certainly goes as far south in East 



