THE GLACIAL RANGE CONTRACTION, ETC. 71 



Area II. There can be no doubt whatever that during 

 the glaciation of the British Area, the range of a very 

 large number of the then indigenous species was con- 

 tracted down to the Iberian Peninsula, and what is now 

 North-west Africa and the Canaries, and that from this 

 area the survivors gradually emigrated northwards as 

 the ice retreated. We find absolute proof of this fact 

 in the traces of that ancient range contraction and 

 subsequent emigration which are still preserved to us 

 in the by no means small number of representative 

 species and races of British birds left behind, especi- 

 ally in the southern portions of this second Refuge 

 Area, when the movement north commenced. At the 

 present time our resident species may be computed 

 at about 115.^ It is a profoundly interesting and 

 significant fact that of these no less than twenty-one 

 species, or more than one-sixth of the whole, are repre- 

 sented in Iberia, North-west Africa, and the Canaries 

 by closely allied species (in some cases two or three 

 distinct representatives) or sub-specific forms whose 

 complete segregation may be retarded or prevented 

 by their interbreeding with the individuals of the typical 

 species which reach that area as winter migrants, not 

 necessarily from the British Islands, but from conti- 

 nental Europe. These species, with their representative 

 forms or species, are shown in the accompanying 

 table. 



^ Probably this is much in excess of the actual number, as many 

 species are largely increased in number by migratory arrivals from 

 northern or eastern areas, and our own breeding individuals may 

 draw south, seeing that many species supposed to be resident with 

 us are well-known winter migrants further south. 



