40 The Migrations of Birds 



are alternating a night or two of travel with often several days of rest and recuper- 

 ation. 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 per- 

 formed; 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 interpreted 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 sub- 

 sidence 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 established 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 shore-line, and those of the second class the location of an inland shallow 

 sea. In other cases there is little evidence of former land connection, for many 

 North American species, even of the smaller land birds, cross the Gulf of Mexico 

 at its widest part. 



The Old World Migratory Quail (Coturnix coturnix} is one of the compara- 

 tively 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 route in a southeasterly direction. When examples 

 from Great Britain were introduced into New England, they adapted themselves 

 readily to their new surroundings and reared young, but when the season for 

 migration arrived the inherited tendency to go in a southeasterly direction asserted 

 itself, and, according to Mr. William Palmer, of the U. S. National Museum, 

 they all passed out into the broad expanse of the Atlantic and were lost. 



For several decades it has been noted that a few species of birds from western 

 Asia have been gradually extending their summer range into northern Scandinavia. 

 When these species migrate, instead of going south through central Scandinavia 

 or southwest along the coast-line, as do the original Scandinavian residents, 



