122 THE MIGRATION OF BIRDS. 



when the Indian Ocean was studded with vast 

 island groups between India and South Africa, 

 forming fly-hnes of migration between Asia and 

 Ethiopia. Nor does it require any great perception 

 to note how the emigrations of certain dominant 

 species, compelled to increase their area in any 

 suitable direction, by over-population or other 

 equally potent causes, extended from island to island, 

 until the two great countries were bridged by an 

 Avian chain, of which many of the links still exist 

 in sedentary birds isolated in South Africa, and of 

 at least a few migratory birds that still continue to 

 cross by a route, most of which has long disappeared 

 beneath the waves ! 



Again, the Knot [Tringa canutus) and the Asiatic 

 Golden Plover {Charadrius fulvus) are two of the 

 last surviving instances of the important route of 

 migration that once ebbed and flowed across tlie 

 Pacific between Asia, New Zealand, and probably 

 Antarctic land. Not only is this route still pointed 

 out by the few migrants that continue to follow it, 

 but its importance as a still more ancient route 

 of emigration is confirmed in a singularly in- 

 teresting manner by the present geographical dis- 

 tribution of various species of Ouzels. Emigra- 

 tion among the important group (Turdinae) of 

 which these birds form a considerable portion, has 

 taken place on a very large scale. That the group 

 is of Polar origin there can be little doubt, and its 

 emigrations have spread far and wide over almost 

 every portion of the earth's surface ; not only 



