BIRD MIGRATION. 35 



now. Therefore when one of these experimental routes proved 

 detiTjnental it was abandoned. 



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

 of energy expended by birds in then* migratory flights. Both the 

 soaring and the sailing of bu'ds 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 vultui-e or a crane, after a few preliminary wing* beats, 

 sets its wijags and mounts in mde sweeping circles to a gTeat 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 \\dngs 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 ^nde reaches of 

 the Caribbean Sea. The humming bird, smallest of aU birds, crosses 

 the Gulf of Mexico, flj'ing 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 aU 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 ah* 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 sufTice to force the bird at a high rate of speed over that 

 2,400-mile course. A thousand-pcmnd 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. 



p:volution of migration routes. 



It has already been stated tliat each of tlie present niigi'ation 

 routes, howfrvcr long, has ])r()bably been of slow growth from an 

 originally short fliglit. In tlie case of many routes it is easy to 

 trace ilie ])roba})lc steps in evolution. Thus the route across tlio 

 (iulf of Mexico, from the mouth oi tlie Mississi])])i to (■ampeche, at 

 the end of the glacial era was undoubtedly a trij) by hiiuf tlirough 

 Texas. As tlie luiid now tlu? Easterji States arose from the (xu^m or 



