only a few degrees from the north pole and migrates to the borders of the 

 antarctic continent is a wonderful traveler. The 22,000-mile journey from 

 one place to the other requires barely twenty weeks. This means that the bird 

 must cover 150 miles a day. Undoubtedly it averages considerably more than 

 this for its side flights in .quest of food must be taken into consideration. 



It would seem that the arctic tern is a lover of the light. At any rate it 

 manages to secure more hours of daylight and sunlight every year than any 

 other living creature for, during at least eight months of the year it lives in 

 a region of perpetual daylight and during the .other four months it lives where 

 the daylight period is much longer than the period of darkness. 



The average weather, rather than the weather which appears to prevail in 

 a migration period of any particular year, determines the dates of migratory 

 movements. That is to say, migration is more a question of climate than of 

 weather. When the travels once begin, however, the weather encountered has 

 some effect in retarding or accelerating the advance more or less. The time 

 of flight appears to be little affected by winds. 



The different species do not follow the same route in migrating. The 

 favorite course extends directly across the Gulf of Mexico. It has generally 

 been believed that after such long continued flights as this most birds are 

 exhausted and are obliged to seek the ground as soon as possible but evidence 

 submitted to the biological survey tends to disprove this supposition. 



As knowledge concerning the flight of birds increases, their marvelous 

 efiiciency as flying machines becomes more and more apparent. The golden 

 plover which in favorable weather is able to cover the 2,400 miles over the 

 ocean between Nova Scotia and South America without stop, remaining some 

 forty-eight hours on the wing, is spoken of as "an aerial machine that is more 

 economical of fuel (energy) than the best aeroplane yet invented." The applica- 

 tion of power in the to-and-fro motion of the bird's wings appears theoretically 

 to be uneconomical since the power required in bringing the wing forward is 

 wasted and at the same time it increases the friction against the air and retards 

 motion forward. The screw propeller of the aeroplane, with no lost motion, 

 would seem a far more efficient form of mechanism, yet- in covering the 2,400 

 miles of its migratory flight the golden plover uses only about two ounces of 

 fuel in the form of body fat. If a 1,000-pound aeroplane could be made as 

 economical of fuel as this bird it could make a 20-mile flight on a single pint 

 of gasoline instead of a gallon as it actually requires. 



The question of how migrating birds find their way has always been a 



puzzling one. Birds are known to return unerringly year after year to old 



nesting places after spending the winter thousands of miles away, flying a 



large part of the distance by night and crossing large bodies of water which are 



devoid of guiding marks. Various theories have been advanced to account for 



this wonderful faculty. One of the latest is that the birds are a sort of 



natural compass and are peculiarly susceptible to the earth's magnetic lines 



of force. It is suggested in the department of agriculture bulletin that they 



find their way by means of a peculiar sense, a sense of direction, which is more 



or less noticeable in humans. ^ ,_ 



365 



