38 BIEDS. 



diverged from each other, we can easily understand how the habit of incipient 

 and partial migration at the proper seasons would at last become hereditary and 

 so fixed as to be what we term an instinct. It will probably be found that every 

 gradation still exists in various parts of the world, from a complete coincidence 

 to a complete separation of the breeding and the subsistence areas; and when 

 the natural history of a sufficient number of species is thoroughly worked out, 

 we may find every link between species which never leave a restricted area in 

 which they breed and live the whole year round, to those other cases in which 

 the two areas are absolutely separated." 



Earlier return of male migrants. In the spring movement of most species of 

 the northern hemisphere the cock birds are always in advance some days or 

 perhaps weeks before the hens. It is not difi&cult to imagine that, in the course 

 of a journey throughout some 50° or 60° of latitude, the stronger should outstrip 

 the weaker. Some observers assert that the same thing occurs in the return 

 journey in autumn. 



Weather. As a rule it would seem as if birds were not dependent on the 

 weather to any great degree. The arrival of seafowl, it is said, is as regular as 

 the almanac itself. Pufiins {F. ardica) repair to some of their stations punctually 

 on a given day as if their movements were regulated by clockwork. Nor is the 

 regularity with which certain species disappear much inferior, for the Swift 

 (C apus) is rarely seen in its summer home in England after the first days in 

 August. 



Routes of migrants. Herr Palmen lays down the chief roads taken by most 

 of the migratory birds of the Palsearctic region in their return autumnal journey 

 southwards from their breeding quarters, and further asserts that in the spaces 

 between these lines of flight such birds do not usually occur. These main routes 

 are nine in number, viz. — 



{A) Leaving the Siberian shores of the Polar Sea, Nova Zembla, and the N. 

 of Eussia, passes down the W. coast of Norway to the North Sea and the British 

 Islands. 



{B) From Spitzbergen and adjoining islands, follows much the same course, 

 but is prolonged past France, Spain, and Portugal, to the W. coast of Africa. 



(C) From N. Russia, and threading the White Sea and Lakes Onega and 

 Ladoga, skirts the Gulf of Finland and the southern part of the £altic to 

 Holstein, and so to Holland, where it divides — one branch uniting with the 

 main route (5), while the other running up the valley of the Rhine, and crossing 

 that of the Rhone, splits up on reaching the Mediterranean, where one path 

 passes down the western coast of Italy and Sicily, a second takes the line by 

 Corsica and Sardinia, and a third follows the S. coast of France and eastern 

 coast of Spain — all three paths ending in N. Africa. 



{D) From the extreme N. of Siberia, ascending the River Ob, branches out 

 near Tobolsk — one track diverging to the Volga, descends that river, and so 

 passes to the Sea of Azov, the Black Sea, and thence by the Bosphorus and 

 iEgean to Egypt ; another track makes for the Caspian by way of the Ural 

 River, and so leads to the Persian Gulf ; while two more are lost sight of on the 

 steppes. 



