THE JOURNEYINGS OF BIRDS. 33 ^ 



bilities of error. For example, meteorological conditions play an im- 

 portant part during migrations, a rain storm or an unusually cold spell 

 may retard progress for days. Even if the conditions are favorable, 

 it is hardly probable that the same individuals migrate for more than 

 a night or two without intermission, so that while the species may be 

 making progress the individuals are alternating a night or two of 

 travel with often several days of rest and recuperation. Again, it was 

 found that most species traveled considerably faster during the latter 

 part of the journey than during the first part. Thus six species 

 showed an increase of 77 per cent, in speed for the northern half of 

 their journey, and the same general result was obtained by calculating 

 the average speed of twenty-five species separately for each of the 

 different months in which migration is performed; the average for 

 March being 19 miles, for April 23 miles and for May 26 miles a day. 

 The species which are late migrants also move faster than those which 

 start earlier and take more time about it. 



The persistence with which birds cling to established lines of 

 travel during the migrations is one of the most remarkable facts within 

 the range of bird life, and this in not a few cases can only be inter- 

 preted in the light of past geological conditions. Thus certain species 

 which breed in Europe and spend the winter in Africa now cross the 

 Mediterranean at one of the widest points, a seemingly needless waste 

 of energy. But soundings between these points have shown that the 

 sea for much of the distance is relatively shallow, and that a moderate 

 subsidence has changed what may have been narrowest to what is now 

 one of the broadest points. This subsidence was undoubtedly slow and 

 first resulted in the formation of a series of islands and lagoons, and 

 the birds easily passed from one island to another, and even after the 

 last bit of land had disappeared they still followed the old route estab- 

 lished by their remote ancestors. 



Many shore and water birds that spend the breeding season in and 

 about the arctic circle to the north of Europe and Asia, follow lines of 

 travel during their migrations that were undoubtedly established under 

 past continental or oceanic conditions. Thus certain species take a 

 circuitous route over what is now a wide expanse of open ocean, while 

 others pass far inland through the Russian and Central European 

 lowlands- Those of the first class are simply still following an ancient 

 shoreline, and those of the second class the location of an inland shallow 

 sea. 



The Old World migratory quail (Coturnix coturnix) is one of the 

 comparatively few migrants among the so-called game birds. During 

 the migrations they wander far from places of their birth, reaching 

 South Africa, Persia and India. The individuals inhabiting Great 

 Britain, or at least a part of them, long ago established a migration 



