BIRDS AND THE WHSTD McMILLAN 359 



without a great amount of lift, the dove must fly rapidly to remain 

 aloft. On his whistling wings he ranges farther than the quail but 

 he falls far short of the yearly journeys of birds with more efficient 

 wings, which use less energy and can maintain lift with less speed. 



Apparently, this speed is, in many cases, surprisingly low. Watch- 

 ing herring gulls from the docks in New Orleans, the writer has seen 

 them hover in light breezes which he estimated to be between 5 and 10 

 miles an hour. Beating their wings very slowly, the gulls matched 

 the velocity of the wind with their own air speed and remained over 

 one spot in relation to the earth without gaining or losing altitude. 

 Even if the larger estimate of the wind's velocity is taken, the resulting 

 figure of 10 miles an hour is far short of the 40-mile speed with which 

 migrating gulls have been credited. 



From personal observation on the airport of New Orleans, where 

 the gulls flock when a stiff wind blows off Lake Pontchartrain, the 

 writer believes that 40 miles an hour is too high for even the maximum 

 speed of the gull. On two occasions when the airways weather station 

 was reporting winds of 27 and 28 miles an hour, only a few of the 

 gulls, when forced to take off, could make headway. These were the 

 young in brown plumage. A few of the adults were able to match the 

 wind but the majority were carried backward and dived to a landing. 

 The maximum air speed of the gull, therefore, would seem not to 

 exceed 30 miles an hour, and may be less. The anemometer is on the 

 roof of a three-story building; none of the birds reached that height, 

 but stayed low where friction was reducing the velocity of the wind. 



The conclusion the writer draws from these observations is that 

 when the migrating gull was timed at 40 miles an hour, he was 

 riding a 30-mile wind. It may be argued, of course, that the gull 

 was flying 30 miles an hour on a 10-mile wind, but that seems 

 contrary to efficiency. Under the dynamic law that pressure in- 

 creases as the square of the velocity, it would take something like 

 nine times the energy to propel the gull at 30 miles an hour that 

 it does at 10. Even if it is granted that a bird can change both his 

 angle of attack and angle of incidence — the angle at which his 

 body and wings strike the air and the angle at which his wings 

 are set to his body — the energy necessary to fly at full speed must 

 be out of proportion to the gain in velocity. To the writer it seems 

 illogical to suppose that a bird, unless forced, frightened, or playful, 

 will fly at anything but the speed at which he uses the least energy. 

 A man can run, but he usually walks. The writer prefers, there- 

 fore, to believe that the gull, when timed, moved through the air a 

 distance of not more than 10 miles while the air itself moved 30 or 

 more and that the gull rode the wind as surely as a man rides who 

 walks through a speeding railroad train. 



