564 Mr. D. A. Banuerman on the [Ibis, 



Hoopoe, Barbary Falcon, Heron, Keutisli Plover, and Yellow- 

 legged Meiring Gull in tlie Canary Archipelago. We must 

 not forget that (as mentioned by Mcinertzhagen) it is pro- 

 bably the environment of the breeding quarters whicli cliiefly 

 influences differentiation. 



Yet again we have numerous other migrants, some arriving 

 in the summer, some in the wititer, while the largest list of 

 all the general visitors contains the Birds of Passage passing 

 to and fro regularly twice a year. In a hundred years time 

 how manj^ of these true Birds of Passage which now pass 

 through the islands will have remained to breed, ceased to 

 pass beyond the Archipelago, and become resident and in 

 their turn differentiated? The biids peculiar to the Canary 

 Islands will, I am convinced, increase in numbers as the 

 years go on. 



Although I maintain that many of the Passerine species 

 got a footing in the Canary Islands in the first in- 

 stance through the agency of regular migration, yet, as 

 Colonel Mcinertzhagen has recently emphasized, there 

 are various types of migration which he groups under 

 the headings of " periodic '"' and " regular '^ migration, 

 "sporadic invasion" or "extensive wanderings," dis- 

 cussed at greater length by Seebohni in his ' Geographical 

 Distribution of the Charadriidse.* Certain birds of the 

 Canaries may well have arrived through the agency of the 

 movements here noted. It is more than likely, for instance, 

 that both the Sand-Grouse and the Courser arrived in the 

 eastern islands during a sudden invasion (immigration), for 

 neither is differentiated in tlie slightest degree. The Great 

 Spotted Wood|)eckeis have, on the contrary, in past years 

 gradually extended their range south until they reached the 

 Canaries ; their course can be [)lainly followed through 

 southern Spain, the Mediterranean islands, and IMorocco (in 

 all of which places local races have been formed), until finally 

 they crossed the sea and formed the two races which now 

 inhabit Tenerife and Gran Canaria. Amongst other examples 

 sprung from European stock whose southern range ceases in 

 the Canary Islands, are the Raven, Chough, Goldfinch, Rock- 



