44 THE MIGRATIOX OF BRITISH BIRDS 



islands is with one exception entirel}- of Pala-arctic 

 derivation, and we have direct proof that the)- were 

 inhabited by Pala;arctic species throughout Pleistocene 

 time, when the breeding range of birds was contracted 

 by extermination down to North-west Africa b)- the 

 devastating ice-sheets which descended upon northern 

 and temperate Europe. The only Ethiopian element 

 in the Canarian avifauna is the Black Oystercatcher 

 {Hceuiatopus capcnsis). There can be no doubt that 

 this species is a very recent emigrant to the islands — 

 a bird gradually extending its range northwards along 

 the now continuous coast-line of Africa ; for we have 

 strong evidence to suggest that when the breeding 

 range of birds of this genus was contracted south by 

 the Glacial Epoch it had no base down the African 

 coast-line beyond the Canaries, the ancient ocean de- 

 fining the range limits in that direction (see Map), but 

 had spread westwards across North Africa from an 

 Ethiopian or Asiatic base. The Black Oystercatchers 

 appear to have been differentiated in and dispersed 

 from a southern hemisphere base. To the present time 

 the Canary Islands are the winter resort of numbers 

 of European species ; they contain many insular forms 

 or representative species of Temperate European or 

 North African forms, and a number of species range 

 from these islands eastwards across the whole of North 

 Africa — facts which seem to suggest a colonizing move- 

 ment during a remote period of continuous land surface, 

 rather than a fortuitous western emigration (of at least 

 50 miles across the sea), especially when we bear in 

 mind the reluctance of birds to cross a wide water area 

 in extending their range from centres of dispersal. 



