THE GLACIAL RANGE CONTRACTION, ETC. 



91 



portant line of North-western Emigration was to the 

 cast of Italy. We must also bear in mind our law {conf. 

 p. 60) that a species in the Northern Hemisphere never 

 normally increases its breeding range in a southerly- 

 direction — hence undoubtedly the absence of such south- 

 eastern species not only from Iberia, and France (in 

 some cases), but practically from the British Area, their 

 lines of Emigration following such a course as to entail 

 a southern — and I maintain an impossible — extension 

 of range in order to reach such countries, from which, 

 however, we already know they are normally entirely 

 absent. \\q see by the instances tabulated above how 

 birds can spread from the south-east even to Scandi- 

 navia, to Germany, and even to France, and yet be 

 rare or abnormal with us and in Iberia, the dominant 

 line of their migrations trending south-eastwards in 

 the exact direction of their ancient north-western lines 

 of emigration. These species have no claim whatever 

 to be regarded as part of our avifauna ; they are all 

 of them uncommon with us, and most probably will 

 ever remain so. 



It is a most astonishing fact that there is not a single 

 common or dominant species passing the British Islands 

 on migration which does not either winter or breed in 

 that area or in Refuge Area II. The great number of 

 birds that occur in our islands sparingly or irregularly 

 every year, neither staying to breed nor to winter, are 

 really migrants out of their usual course, and belong ta 

 species whose dominant line of flight normally trends 

 south-east. Comparatively speaking, a few individuals 

 of the species in the above table, marked with an 

 asterisk, regularly pass down the west coasts of Europe 



