ISLAND AVIFAUNAS 201 



ing, singularly rich in endemic forms ; in fact no other 

 group of islands in the West Palaearctic region can boast 

 so many peculiar races or such abundant examples of 

 insular variation. The explanation is a very simple 

 one, and the facts confirm in no uncertain way the truth 

 of our general arguments respecting island avifaunas. 

 The number of endemic races may be taken at ten, 

 although this does not quite represent the peculiarities 

 of the islands, for several species and races not included 

 in that total are apparently common to Madeira and 

 the Azores as well. Of these ten no less than three are 

 island forms of two endemic species, confined to various 

 parts of the Canarian Archipelago, some of which 

 apparently interbreed among themselves. How have 

 these endemics become differentiated, and how do they 

 continue to preserve their characteristics .? It will be 

 remarked that not one of them is an endemic race of a 

 species that now visits the islands on migration, or at 

 least that portion of the archipelago inhabited by the 

 peculiar form. They are all allied either to North-west 

 African sedentary species, or to birds that breed in 

 Europe and North-west Africa, yet do not extend their 

 winter migrations to the islands. When the Canaries 

 formed one unbroken area with the Atlas, there can be 

 no reasonable doubt that these endemic species were 

 not in existence. Being sedentary throughout this area, 

 they have — as submergence or volcanic action gradually 

 or suddenly reduced it to an archipelago — continued to 

 inhabit the localities where they were so isolated, and 

 have thus been able to preserve the differences which 

 now entitle them to specific or subspecific rank. It is 

 interesting to remark that the Canarian form of the 



