Itrh N^uiB 



Devoted to the Interests of the Bird Fancier 



yolume I. 



SEPTEMBER-OCTOBER, 1909 



U{umber 5 



Wind and Migration. 



The relationship of wind to birds 

 during migration is a subject of much 

 interest and while no constant, fixed 

 relationship has been noted, there is 

 much of a scientific value in the many 

 observations which have been from 

 time to time recorded. 



Mr. F. Stubbs recently presented 

 some compiled observations before 

 the Manchester Philosophical Society, 

 which are worthy of our considera- 

 tion. 



The head-wind theory is fairly 

 popular but some writers have shown 

 signs of leaning towards a contrary 

 opinion. Mr. Clarke, British Associa- 

 tion Records, says "strong winds 

 have a curious effect on the flight of 

 gulls, compelling them to move in a 

 direction more or less directly head- 

 ing the wind. Thus a strong wester- 

 ly wind causes great numbers of gulls 

 to seek the estuaries and bays of our 

 east coast. On the other hand, 

 strongly westerly winds will fill the 

 estuaries and sea-locks of the west 

 coast with these birds. Yarrell says: 

 "It by no means follows that the di- 

 rection of the wind, with which the 

 birds drop on the land, is the same 

 as that prevailing at a greater eleva- 

 tion." 



Stubbs says, accepting the Head- 

 wind Theory, "To the observer on the 

 coast the velocity of the wind must 

 be at least ten miles an hour. At an 

 elevation of say 500 feet, allow 20 

 miles an hour. A Goldcrest,, a fami- 

 liar migrant, desires to cross the 

 North Sea. a distance of 2.50 to 3-50 

 miles. We may call it for the pres- 



ent 300 miles and allow the bird a 

 velocity of 2.5 miles an hour. In a 

 perfectly calm atmosphere the jour- 

 ney would occup 12 hours. When 

 the so-called favorable head wind is 

 blowing, the part of the earth's at- 

 mosphere lying over Western Europe 

 is moving eastward at, say, 15 miles 

 an hour. The bird has thus to make 

 its journey on a supporting medium 

 in an opposite direction. In one hour 

 it will have flown 25 miles through 

 that body of air, but during the same 

 time the aerial mass has moved 15 

 miles eastward. Between two points 

 on the earth's surface the bird will 

 have traveled no more than 10 miles. 

 At this rate the journey will take 30 

 hours. It should be quite evident 

 that no bird can make any headway 

 against a wind with a greater velo- 

 citythan its own speed of flight. 



The general opinion seems to be 

 that when a bird flies head to wind 

 the air rushes past it at a total velo- 

 city which is that of the wind plus 

 the velocity of the bird. Of course, 

 this would be true in the case of a 

 steamer or a swimming bird. But it 

 is absurd to assume that it is so in 

 the case of a flying bird, or even in 

 the case of a swimmer in a strongly 

 flowing current; the bird and the 

 swimmer are wholly in a moving sup- 

 porting medium. It is not safe to 

 study avian flight by the aid of sail- 

 ing ships. A ship is supported by the 

 water but propelled by the air. The 

 bird is supported by the air and pro- 

 pelled by its wings. Stubbs continues: 



"Most of us, especially outdoor ob- 

 servers, form conceptions of the wind 

 which are altogether wrong. We are 



