200 BRITISH BIRDS. 



from Persia, through Turkestan and Cashmere, along the mountains 

 of South-west Siberia as far east as Krasnoyarsk and Yenesaisk; and 

 in the latter locality appears to have driven out the White Wagtails and 

 to have divided them into two colonies. As I ascended the Yenesay 

 from the Arctic circle the White Wagtail abounded on the banks of the 

 river until I neared Yenesaisk about lat. 59, when suddenly it disappeared, 

 and its place was taken by M. personata; but about halfway between 

 Yenesaisk and Lake Baikal, Middendorff found the White Wagtail again, 

 and Taczauowsky describes it as common near Lake Baikal and in West 

 Dauria. The isolation of this colony appears to have been facilitated by 

 the fact that in autumn the birds migrate eastward instead of westward to 

 winter in West China, Burma, and India. Some ornithologists have 

 described birds from this colony as distinct under the name of M. duk- 

 himensis ; but I am unable to detect any difference between examples from 

 Lake Baikal, North Siberia, India, or Spain. North-west European 

 examples have somewhat narrower white margins to the wing-coverts. 



The British ornithologist who leaves his native island and crosses over 

 to the continent may ramble over any farm on the shores of the German 

 ocean without finding much difference between the birds of the two 

 countries. Most of them he will recognize as old acquaintances ; a few 

 which he looked upon as great rarities in England he will find to be 

 common on the other side of the water; and some which at the first glance 

 he may suppose to be common British birds, he will find on closer exami- 

 nation to differ slightly from their insular representatives. To the latter 

 group belongs the White Wagtail. On the continent from Calais to 

 Hamburg this bird everywhere takes the place of the Pied Wagtail. The 

 two birds have the same habits, nearly the same song and call-notes, make 

 a similar nest, and lay similar eggs. There seems to be no difference be- 

 tween them whatever, except in the colour of the back and the sides of the 

 neck. The Pied Wagtail is obviously an island form of the White Wag- 

 tail, and has probably been differentiated since the passing away of the 

 Glacial epoch. During the warm climate which appears to have succeeded 

 this cold period in these latitudes, the White Wagtails of the British 

 Islands were probably isolated from their continental brethren, and 

 possibly having fewer enemies (both birds and beasts of prey being com- 

 paratively less abundant on islands than on continents) sexual selection 

 was not prevented by protective selection from providing them with a 

 special bridal dress at the spring moult. In those days the isolation of the 

 two areas of distribution was probably complete ; and we may fairly assume 

 that the two species only began to invade each other's territory in com- 

 paratively recent times, since the winters have become sufficiently cold to 

 compel them to be more or less migratory in their habits. Hence we find 

 that although the White Wagtail is so rare in our islands, it is not, like 



