2 CIRCULAR 42S, U. S. DEPARTMENT OF AGRICULTURE 



The speed of birds, especially of game birds, has been greatly 

 exaggerated, both in literature and in popular thought, because it 

 has usually been computed from estimates rather than from exact 

 measurements; and the most reliable of these estimates has been 

 based on the estimated distance of the bird from the hunter, the 

 estimated "lead" necessary to hit the bird — that is, the distance 

 traveled by the bird from the time the gun was fired until the bird 

 was struck by the shot — and the time required for the shot to travel 

 from the gun to the bird. If all three factors were known exactly, 

 the speed of the bird could be accurately computed, but, unfortunately, 

 only the velocity of the shot is definitely known. Also it has been 

 foimd recently by experiment that there is an appreciable loss of time 

 in piilling the trigger. Against the sky it is practically impossible 

 to gage the exact distance of the bird, and the distance it travels may 

 be exaggerated because momentum will carry a shot bird some 

 distance before it falls. As can be readily understood, an overesti- 

 mate of a very few feet in these figures will result in the computation 

 of a series of very high speeds for game birds, which many persons 

 have believed possible. Gunners (possibly actuated in part by a 

 subconscious feeling of personal vanity), especially, have been prone 

 to attribute speeds of 75, 100, or even 150 miles an hour to ducks — 

 thev missed. 



MEASURED SPEEDS 



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 

 scattered notes and some extensive papers. Stop watches and theod- 

 olites 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, especially 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 other atmospheric conditions. Undoubtedly, the air speeds of 

 different birds are much more comparable than ground speeds, since 

 variables other than the flying ability of the individuals are reduced 

 to a nimimuni. Air speeds are difficult to obtain, however, since the 

 only means is by the air-speed indicator of airplanes, and the stalling 

 speed of most airplanes is higher than the maximum possible for any 

 but the fastest flying species. Most records thus obtained are of 

 birds chased and indicate, therefore, the greatest speed of which the 

 birds were capable: the "stalling speed" of birds will forever remain 

 a matter of conjecture. The ground speed, however, can be measured 

 more readily, though it is subject to much variation, and the condi- 

 tions under which observations are made vary so greatly that two 

 records, even for the same species, are seldom entirely comparable. 



VARIATIONS IN SPEED 



Xo hard and fast rules can be laid down as to bird speeds, not even 

 for any given species, since the individual variation is considerable. 



