1919-] Geographical Distribution and Migration. 385 



distribution that expansion has followed coast-lines, which, 

 as pointed out by Hartert (Novit, Zool. xx. 1913, p. 76), 

 is a tendency not only among migratory but among such 

 sedentary species as the White Owl, Chough, Cirl-Bunting, 

 and others. But here, in the case of Galerida cristata, we 

 see expansion and differentiation progressing concurrently ; 

 and there can be little doubt that the Crested Lark, a hardy 

 species capable of residence in the snows of central Europe 

 and Asia or in the heat of the Red Sea littoral, will not 

 check its expansion till the Cape Seas arrest its progress. 

 Its advent on the west coast of Europe is probably of com- 

 parative recent date, for it has never established itself in 

 Great Britain, though there can be little doubt it would have 

 done so during the last century if its efforts had not been 

 checked by the greed for rare birds. 



The Shore-Lark {Eremophila alpestris flava), which in 

 comparatively recent times has become a common breeding- 

 species in Arctic Norway, affords a good illustration of 

 gradual expansion to the west. At the same time as ex- 

 pansion of breeding-range, these birds opened out a new line 

 of migration about 18i7 (Gaetke) and became a common bird 

 of passage at Heligoland in spring and autumn. This fact is 

 of particular interest, as other northern species (P/ujlloscopus 

 borealis borealis, Anthns gustavi, and Emberiza pusilla) have, 

 in spite of westward extension of their breeding-range, rigidly 

 adhered to their ancient migration-route and winter-quarters 

 in south-east Asia. Cooke ('Migiation of Birds,' p. 6) further 

 illustrates the phenomenon of westward extension in the 

 Bobolink, which species rigidly adhered to its ancient 

 migration-route though adding 1000 miles to its line of 

 flight. 



Gradual expansion to the north can be found in the case 

 of the Greater Spotted Woodpecker in Great Britain and in 

 the case of Passer moabiticus moabiticus. This latter bird, 

 formerly confined to the south end of the Dead Sea, is 

 now commonly found in the Jordan Valley at the north 

 end of the Dead Sea and will doubtless extend to Galilee. 



Eastward expansion, though the example must be taken 



