hour after hour along the windward side of a ship, are now utilized 

 by man in his operation of gliders. Moreover, the whole structure of 

 a bird renders it the most perfect machine for extensive flight that the 

 world has ever known. Hollow, air-filled bones, making an ideal 

 combination of strength and lightness, and the lightest and toughest 

 material possible for flight in the form of feathers, combine to produce 

 a perfect flying machine. Mere consideration of a bird's economy of 

 fuel or energy also is enlightening. The golden plover, traveling 

 over the oceanic route, makes the entire distance of 2,400 miles from 

 Nova Scotia to South America without stop, probably requiring about 

 48 hours of continuous flight. This is accomplished with the con- 

 sumption of less than 2 ounces of fuel in the form of body fat. To be as 

 economical in operation, a 1,000-pound airplane would consume in a 

 20-mile flight not the gallon of fuel usually required, but only a single 

 pint. 



The sora, or Carolina rail, which is such a notoriously weak flyer that 

 at least one writer was led to infer that most of its migration was made 

 on foot, has one of the longest migration routes of any member of the 

 family, and easily crosses the wide reaches of the Caribbean Sea. The 

 tiny ruby-throated hummingbird crosses the Gulf of Mexico in a single 

 flight of more than 500 miles. 



While birds that have recently arrived from a protracted flight over 

 land or sea sometimes show evidences of being tired — as, for example, 

 pintail ducks that have flown from the North American mainland to 

 the Hawaiian Islands — their condition is far from being a state of ex- 

 haustion. With a few hours' rest and a crop well filled with proper 

 food, most birds exhibit eagerness to resume their journey. The popu- 

 lar notion that birds find the long ocean flights excessively wearisome 

 and that they sink exhausted when terra firma is reached, generally 

 does not agree with the facts. The truth lies in the opposite direction, 

 as even small land birds are so little averse to ocean voyages that they 

 not only cross the Gulf of Mexico at its widest point, but may even pass 

 without pause over the low, swampy coastal plain to the higher regions 

 beyond. Under favorable conditions birds can fly when, where, and 

 how they please. Consequently the distance covered in a single flight 

 is governed chiefly by the food supply. Exhaustion, except as the re- 

 sult of unusual factors, cannot be said to be an important peril of 

 migration. 



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