SPEED OF FLIGHT AND MIGRATION 



There is a widespread misconception among people concerning the 

 speed at which birds can fly. One often hears stories of birds fly ing "a 

 mile a minute." While undoubtedly some birds can and do attain this 

 speed, such cases are exceptional, and it is safe to say that, even when 

 pressed, few can develop an air speed of 60 miles per hour. Birds 

 generally have two greatly differing speeds, one being the normal 

 rate for ordinary purposes, and an accelerated speed for escape or 

 pursuit. All birds, except the heavy-bodied, small-winged species 

 such as auks, grebes, and other divers, have a reserve speed that may 

 be double the normal rate. 



Although it was thought for a long time that migratory flights 

 were made at normal cruising speeds, Harrison (1931) and 

 Meinertzhagen (1955) showed that migration speeds were in between 

 cruising speeds and escape speeds. The theory that migrating birds 

 attain high speeds received encouragement from the German 

 ornithologist Gatke (1895) who, for many years, observed birds at the 

 island of Heligoland. He postulated that the bluethroat, a species of 

 thrush smaller than the American hermit thrush, could leave 

 African winter quarters at dusk and reach Heligoland at dawn; this 

 flight would mean a sustained speed of 200 miles per hour! He also 

 thought the American golden plover flew from the coast of Labrador 

 to Brazil in 15 hours at the tremendous speed of 250 miles per hour. 

 Most ornithologists now consider these conclusions to be unwarrant- 

 ed. 



Reliable data on the speed of birds are accumulating slowly. 

 Accurate measurements are difficult to obtain unless the bird travels 

 over a measured course and wind conditions at the level of flight are 

 known. Several subtle factors, besides wind and pursuit, can 

 influence the speed of a flying bird. For instance, species that have a 

 courtship flight often reach their maximum speeds then. Small 

 woodland birds often fly faster across an open area where they might 

 be attacked by a bird of prey than under cover where there is less 

 danger. Birds in flocks generally fly faster than when flying alone. A 

 thermal draft may induce an almost imperceptible air movement at 

 the Earth's surface, but a good glider with motionless wings may 

 make 35 miles per hour on a current of air that is rising vertically at 

 less than 2 miles per hour. If the bird coasts downhill at a slight angle 

 in still air, it can attain a similar speed. 



For sustained flight, it may be generally concluded that larger 

 birds fly faster than smaller birds. A common flying speed of ducks 

 and geese is between 40 and 50 miles per hour, but among the smaller 

 birds it is much less. Herons, hawks, horned larks, ravens, and 



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