FLIGHT SPEED OF BIRDS 3 



For example, Portal (55), in 1922, noted that one partridge of a covey 

 flew 15 percent faster than the others when all were in full flight 

 before a falcon. The age of the bird, the state of its plumage, and 

 other physical conditions modify its powers of flight and thus affect 

 its speed. Variation in speed, as stated above, is caused also by the 

 force of the wind and other atmospheric conditions. 



Moreover, it is only in level flight that birds can be timed or their 

 speeds compared, since even a slight angle downward adds greatly to 

 the velocity. It is practically impossible to time the speed of ducks 

 darting down to the water, the stoop of a hawk, or the swoop of a 

 swift. Some falconers have estimated that when a peregrine strikes 

 its prey it is traveling at the rate of 150 miles an hour. An aviator 

 has related that on one occasion when he was diving at a flock of ducks 

 at a velocity of nearly 175 miles an hour, a hawk (presumably a duck 

 hawk) passed him "as though the plane were standing still" and struck 

 one of the ducks. In this connection it is interesting to note that 

 aviators report that ducks, when pressed, accelerate considerably, 

 possibly increasing their speed by a third, but that geese are able to 

 accelerate very little. 



EFFECT OF WINGS AND WEIGHT 



The size and shape of the wings in comparison with the weight of a 

 bird are important factors in determining its speed of flight. The 

 smaller the wings in proportion to the weight, the greater will be the 

 speed required for the bird to maintain its position in the air. More 

 rapid wingbeats against the supporting atmosphere are necessary for 

 a bird with a small wing surface than for one with a wing surface 

 great enough for it to take full advantage of ascending air currents. 

 The short-winged loon has much difficulty in raising its heavy body 

 from the water, but once it is in the air, its rapid wingbeats carry it 

 away at great speed, whereas the turkey vulture, with its long, broad 

 wings and light body can rise easily and sail lazily on the air without 

 an}- detectable wing movement. The loon, which weighs more than 8 

 pounds, has a wing expanse of about 55 inches, but the turkey vulture, 

 with only a 4-pound body weight, is supported by a wingspread of 

 about 70 inches. Although the weights of the mallard and canvasback 

 are nearly the same, the wing surface of the slow-flying mallard is 

 about 20 percent greater than that of the swifter canvasback, the latter 

 making up for this smallness of supporting surface by the rapidity of 

 its wingbeats, aided probably also by a reduction of air resistance 

 because of its more streamlined build. 



It is generally conceded that when two birds of a similar type are 

 once in the air, the heavier bird is the faster. The quicker rise and 

 get-away of the smaller bird, the teal, for example, gives a false 

 impression of speed. Radclyffe (59), an experienced falconer, in Eng- 

 land, related that he had often flown a peregrine over mixed flocks of 

 teals and mallards and flushed the birds simultaneously. In every 

 case, the first bird overhauled by the hawk was a teal ; and in case of a 

 long flight, when every bird was flying for its life, the farther the birds 

 went, the more the teal lagged behind. Munson (51) reported that 

 while chasing ducks with an airplane, he twice saw bunches of green- 

 winged teals that were easily outflown by canvasbacks in the same 

 flock. 



