SPEED OF FLIGHT 41 



SPEED OF FLIGHT 



"There is a wide-spread misconception concerning the speed at 

 which birds normally fly, and even regarding the speed they can attain 

 when occasion demands, as when closely pursued by an enemy. It is 

 not unusual to hear accounts of birds flying 'a mile a minute.' While 

 undoubtedly some birds can and do attain a speed even greater than 

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

 pressed, few can develop an air speed of 60 miles an hour. They do, 

 however, have two speeds, one being the normal rate for every-day pur- 

 poses and also for migration, and an accelerated speed for escape or 

 pursuit; this in some cases may be nearly double the normal rate of move- 

 ment. Nevertheless, the effort required for the high speeds could not be 

 long sustained, certainly not for the long-distance migratory journeys 

 that are regularly made by most birds. 



"Sportsmen also often greatly overestimate the speed at which ducks 

 and geese fly and sometimes attempt to substantiate their estimates by 

 mathematical calculations, based upon the known velocity of a charge 

 of shot, the estimated distance, and the estimated 'lead' that was neces- 

 sary to hit the bird. If all three elements of the equation were known 

 with certainty, the speed of the birds could be determined with a fair 

 degree of accuracy. The majority of the ducks that are reported as 

 killed at 40, 50, or even 60 yards, however, actually are shot at dis- 

 tances much less than estimated. To sight along a gun barrel and esti- 

 mate correctly the distance of a moving object against the sky is so 

 nearly impossible for the average gunner as to make such calculations 

 of little value. 



"During the past few years reliable data on the speed of birds have 

 accumulated slowly. It has been found that the common flying speed 

 of ducks and geese is between 40 and 50 miles an hour, and that it is 

 much less among smaller birds. Aviators have claimed that at 65 miles 

 an hour they can overtake the fastest ducks, though cases are on record 

 of ducks passing airplanes that were making 55 miles an hour" (Lincoln, 

 1935). 



"In the last quarter of a century the effort to ascertain the facts on 

 the speed of avian flight has resulted in the publication of many scat- 

 tered notes and some extensive papers. Stop watches and theodolites 

 have been used to time birds flying across measured distances, and the 

 automobile speedometer and the air-speed indicator of the airplane have 

 furnished many reliable records. These data are demonstrating that the 

 earlier estimates of bird speed were too high and that some birds, espe- 

 cially the song and insectivorous species, are rather slow flyers. 



"Most persons are less interested in air speed than in ground speed. 

 Air speed is the rate at which a bird moves through the air by its own 

 effort, no allowance being made for the influence of the wind. Ground 

 speed is the velocity of the actual progress of the bird between two points, 

 or the air speed accelerated or retarded by the influence of the wind and 



