THE GLACIAL RANGE CONTRA CTI OX, ETC. 79 



are only abnormal winter visitors to the British Islands, 

 or, what is much more likely, may have once bred there 

 and become exterminated {conf. pp. 183 — 186). If this 

 be not a true interpretation of the facts, we are con- 

 fronted with an insurmountable difficulty of Distribution, 

 for we should find the anomaly of five species breeding 

 and wintering south of us in Iberia, North-west Africa, 

 and elsewhere, but wintering only in our area. The 

 mild southern counties of our country enable individuals 

 of these species to winter at or near the northern limit 

 of their distribution. There can be little doubt that the 

 two Passerine species would ultimately become residents 

 again in our area if left unmolested ; the three larger 

 species would possibly become so if our islands were not 

 so thickly populated, or the individuals that reach us 

 were not so promptly exterminated. I may here also 

 take the opportunity of remarking that we have not a 

 single species wintering in the British Islands and South- 

 eastern Europe, and absent from South-western Europe 

 and North-western Africa (although many of course 

 winter in both), which is a most suggestive fact, indicat- 

 ing the sources of our avifauna and its Refuge Areas 

 or Range Bases during glacial times. 



When we come to deal with the Summer Visitors to 

 the British Islands, the vast importance of Refuge Area 

 11. is demonstrated in no uncertain way. This Refuge 

 Area continues down to the present time to be the 

 winter home of almost every bird that migrates to our 

 country in spring to breed. The following table indi- 

 cates the species and the precise winter habitat of each, 

 or, in cases of wider dispersal, of the individuals of such 

 species that breed in Western Europe. 



