BIRD MIGRATION. ,'}5 



now. Therefore when one of these experimental routes proved 

 detrimental It was abandoned. 



In this connection it may be well to consider the actual amount 

 of energy expended by birds in their migratory flights. Both the 

 soaring and the sailing of birds show that they are proficient in the 

 use of several factors in the art of flying that have not yet been 

 mastered either in principle or practice by the most skillful of modern 

 aviators. A vulture or a crane, after a few preliminary wing beats, 

 sets its wings and mounts in wide sweeping circles to a great height, 

 overcoming gravity with no exertion apparent to human vision even 

 when assisted by the most powerful telescopes. The Carolina rail, 

 or sora, has small, short wings apparently ill adapted to protracted 

 flight, and ordinarily when forced to fly does so reluctantly and alights 

 as soon as possible. It flies with such awkwardness and apparently 

 becomes so quickly exhausted that at least one writer has been led to 

 infer that most of its migration must be made on foot ; the facts are, 

 however, that the Carolina rail has one of the longest migration 

 routes of the whole rail family and easily crosses the wide reaches of 

 the Caribbean Sea. The humming bud, smallest of all birds, crosses 

 the Gulf of Mexico, flying over 500 miles in a single night. As already 

 noted, the golden plover flies from Nova Scotia to South America, 

 and in fair weather makes the whole distance of 2,400 miles without a 

 stop, probably requiring nearly if not quite 48 hours for the trip. 



Here is an aerial machine that is far more economical of fuel — 

 i. e., of energy — than the best aeroplane yet invented. The to-and- 

 fro motion of the bird's wing appears to be an uneconomical way of 

 applying power, since all the force required to bring the wing for- 

 ward for the beginning of the stroke is not only wasted, but more 

 than wasted, as it largely increases the air friction and retards the 

 speed. On the other hand, the screw propeller of the aeroplane 

 has no lost motion. Yet less than 2 ounces of fuel in the shape of 

 body fat suffice to force the bird at a high rate of speed over that 

 2,400-mile course. A thousand-pound aeroplane, if as economical of 

 fuel, would consume in a 20-mile flight not the gallon of gasoline 

 required by the best machines but only a single pint. 



EVOLUTION OF MIGRATION ROUTES. 



It has already been stated that each of the present migration 

 routes, however long, has probably been of slow growth from an 

 originally short flight. In the case of many routes it is easy to 

 trace the probable steps in evolution. Thus the route across the 

 Gulf of Mexico, from the mouth of the Mississippi to Campcche, at 

 the end of the glacial era was undoubtedly a trip by land through 

 Texas. As the land now the Eastern States arose from the ocean or 



