rarely above 200 feet. During the World Wars broad areas in the air 

 were under constant surveillance and among the airplane pilots and 

 observers many took more than a casual interest in birds. Of the 

 several hundred records resulting from their observations only 36 were 

 of birds flying above 5,000 feet, and only 7 above 8,500 feet. Cranes 

 were once recorded at an altitude of 15,000 feet, while the lapwing 

 was the bird most frequently seen at high levels, 8,500 feet being its 

 greatest recorded altitude. 



These observations naturally relate only to daytime travelers, but 

 there is no reason to believe that nocturnal migration is performed at 

 higher altitudes. The fact that many birds are killed each year by 

 striking the lanterns at lighthouses, or other man-made obstructions, 

 does not, however, furnish conclusive proof that low altitudes are gen- 

 erally used during nocturnal flight, for it should be recalled that these 

 accidents occur chiefly in foggy or unsettled weather, and also that 

 powerful lights have a great attraction for many species of birds. The 

 altitude at which birds travel is affected by other weather conditions 

 also. For example, flight at the higher elevations is facilitated on 

 clear, warm days by the currents of warm air that ascend from broad 

 areas. 



Orientation 



1 here probably is no single aspect of the entire subject of bird migra- 

 tion that challenges our admiration so much as the unerring certainty 

 with which birds cover thousands of miles of land and water to come 

 to rest in exactly the same spot where they spent the previous summer 

 or winter. The records from birds marked with numbered bands 

 offer abundant proof that the same individuals of many species will 

 return again and again to their identical nesting sites. These data 

 show also that many individuals migrate in fall over the same route, 

 year after year, making the same stops and finally arriving at the 

 precise thicket that served them in previous winters. 



The faculty that enables these birds to point their course accurately 

 over vast expanses of land and water may, for want of a better term, 

 be called a "sense of direction." Man recognizes this sense in himself, 

 though usually it is imperfect and frequently at fault. Nevertheless 

 the facility with which experienced hunters and woodsmen locate tiny 

 camps or other points in forested or mountainous country, frequently 

 cloaked by darkness or fog, with all recognizable landmarks obliterated 



28 



