appears to be between 500 and 1,000 feet (Bellrose 1971), but radar 

 studies have found some nocturnal migrants (probably shorebirds) 

 over the ocean were at 15,000 or even 20,000 feet (Lack 1960b; Nisbet 

 1963b; Richardson 1972). Observations made from lighthouses and 

 other vantage points indicate that certain migrants commonly travel 

 at altitudes of a very few feet to a few hundred feet above sea or land. 

 Sandpipers, northern phalaropes, and various sea ducks have been 

 seen flying so low they were visible only as they topped a wave. 

 Observers stationed at lighthouses and lightships off the English 

 coast have similarly recorded the passage of landbirds flying just 

 above the surface of the water and rarely above 200 feet. During the 

 World Wars, broad areas in the air were under constant surveillance, 

 and many airplane pilots and observers 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. Records of the 

 U.S. Civil Aeronautics Administration show that over two-thirds of 

 all the bird-aircraft collisions occur below 2,000 feet and practically 

 none occur above 6,000 feet (Williams 1950). 



Recently, radar has aided greatly in determining differences in the 

 altitude of bird flight. Nocturnal migrants appear to fly slightly 

 higher, on the average, than diurnal migrants, but daytime flights 

 may be influenced more by cloud cover (Lack 1960a; Eastwood and 

 Rider 1965). Bellrose (1971) found little difference in the altitudinal 

 distribution of small nocturnal migrants under clear or overcast 

 skies. Many night migrating birds are killed each year by striking 

 lighthouses, television towers or other man-made illuminated 

 obstructions, but this does not furnish proof that low altitudes are 

 generally used during nocturnal flight because these accidents occur 

 chiefly in foggy weather. Under such conditions, migrating birds 

 seem to be attracted to and confused by lights. Seabirds, such as 

 loons, eiders, and scoters, generally fly very low over the water but 

 gain altitude when land is crossed. The reverse is true for landbirds 

 (Dorst 1963; Bergman and Donner 1964; Eastwood and Rider 1965). 

 There may be a seasonal difference in the altitude of migration, but 

 the evidence is conflicting. Radar echoes studied by Bellrose and 

 Graber in Illinois (1963) showed fall migrants flew higher than 

 spring migrants. They speculated this difference was related to the 

 winds during the fall being more favorable for southerly migration 

 at higher altitudes, while winds at these altitudes in the spring would 

 be less favorable for northerly migration. Eastwood and Rider (1965) 

 studied seasonal migration patterns in England and found the 

 reverse to be true. They suggested one reason for this seasonal 

 difference was that flocks of fall migrants included many young 

 birds whose flight capabilities are inferior to adults and 

 consequently are unable to achieve the higher altitudes in the fall. 



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