4 CIRCULAR 428, U. S. DEPARTMENT OF AGRICULTURE 



In comparing birds of dissimilar types, rapid wingbeats or erratic 

 flight sometimes give the erroneous impression of great velocity. A 

 black-headed gull with deliberate wingbeat was noted (41) almost to 

 keep pace with a golden plover whose rapidly moving wings made it 

 appear much swifter. The seeming speed of the swallow is partly due 

 to its constant twisting and turning. 



INFLUENCE OF WIND 



Wind causes wide variation in the speed of bird flight, even of 

 different individuals of the same species. Probably most of the high- 

 speed records are of birds driven by the wind, but to consider that a 

 bird's progress over the earth will be at the rate of its air speed plus 

 or minus the exact force of the wind can hardly be correct. Brown 

 pelicans were repeatedly timed (66) along the beach near El Pismo, 

 Calif. The birds were flying south and the prevailing wind was from 

 the northeast. With practically no wind, their speed was only 14 

 miles an hour; with "half a gale" blowing, it increased to only 16 miles 

 an hour; and when the velocity of the wind reached 50 miles an hour, 

 it rose to but 22 miles an hour. 



The explanation is that in order for a bird to remain aloft it must 

 rest on a current of air against the under side of its wings, and this 

 current must come from the front, not from behind, the backward tilt 

 of the wings catching this wind. These facts are well recognized in 

 modern aeronautics. Both birds and airplanes must take off and land 

 into the wind. Therefore, if the wind is directly behind, the bird 

 must move its wings faster in order to get the necessary upbearing 

 current or else be blown along by the wind without being able to guide 

 its course. Gulls are frequently seen drifting with a ship on the wind- 

 ward side, borne along with almost motionless wings on the updraft 

 of air from the wind striking against that side of the ship, although 

 the birds on the other side, where the draft is downward, must flap 

 their, wings steadily. Birds dislike to fly directly with the wind and 

 direct their course so as to have the wind at one side or even to fly 

 directly into it. An Army homing pigeon, in many trial flights, made 

 its maximum speed of a mile a minute only when helped by a quartering 

 tail wind. 



That birds are sometimes unable to cope with the wind is indicated 

 by the many records ("accidental occurrences") of birds far from their 

 normal range, following storms. Usually such records are for a few 

 individuals only, but late in December 1927 hundreds of lapwings 

 appeared in Newfoundland. The lapwing is a European species of 

 which less than a dozen individuals had previously been recorded in 

 North America. Among the birds captured at that time was one that 

 had been banded in northern England, indicating the probable source 

 of many of these birds. Witherby (82), in his study of this event, 

 stated that the birds probably headed southwestward for southern 

 Ireland but that an east wind stronger than their power of flight was 

 at that time blowing across the North Atlantic and doubtless drove 

 the birds far beyond their intended destination. B. (11), an observer 

 in England, tells of seeing rooks helpless against a strong wind, as 

 they attempted to reach their roost, some being blown sideways and 

 some tail first and one turning a series of somersaults head over tail, 

 when a wedge of pink-footed geese passed, flying low into the gale. 

 The geese rolled heavily from side to side but kept straight on their 



