THE GLACIAL RANGE CONTRACTION, ETC. 99 



and very irregular migrant to the Canary Islands.^ 

 Did the individuals breeding in Holland and South 

 Sweden migrate down West Europe, — of which, how- 

 ever, we have no evidence, — then by a well-known law 

 they should go to the Cape ; but as they are birds 

 breeding at the limits of the northern range, they go the 

 furthest south, and by a route which misses South-west 

 Europe altogether ! Very similar remarks apply to the 

 Black Stork. The Red-crested Pochard {Fiiligula 

 riLJind) may be cited as another instance. There can 

 be little or no doubt that the individuals of this species 

 breeding in Europe north of Italy and east of France 

 are the descendants of emigrants from the far east, 

 inasmuch that the bird is very rare in the East Mediter- 

 ranean and in Egypt, but can be traced through the 

 basins of the Black and Caspian Seas to Turkestan and 

 North Persia, thence through Afghanistan to the Refuge 

 Area or pre-glacial Range Base in India. The indi- 

 viduals breeding in Spain, Sicily, Sardinia, and Southern 

 Italy form part of the colony whose pre-glacial range 

 extended to North-west Africa, where they are also 

 residents. 



Very interesting evidence in support of this line of 

 Emigration is furnished by the Blue-headed Wagtail 

 {JMotacilla flavd), and its several allied forms. The 

 Blue-headed Wagtail is only an abnormal migrant to 

 the British Islands, which are entirely beyond the con- 



^ There can be no doubt whatever that the Knots {Tringa 

 canutics), passing our coasts on migration, reach their winter 

 quarters in Africa by a route east along the Mediterranean and 

 south-west across Africa to the west coasts as far as Damara Land. 

 It is significant that this bird is unknown on the Canaries. 



