In their juvenile wanderings, young ducks move from one marsh to another. 



merits, as discussed in Chapter 5. Once the bird leaves the familiar range, 

 once it has no geographical goal, once it wanders at random, the over-all 

 trend will be in the direction of the wind (Figure 25). In their explora- 

 tions, the juveniles may travel part of the time against the wind, some- 

 times for prolonged periods, for the bird is not passively at the mercy of 

 the wind as a leaf or wisp of spider's web. But as long as the travel is ran- 

 dom, the total product of a day's or a week's wandering will be in the 

 direction in which the air mass flows, just as surely as a ship wandering 

 in the Gulf Stream moves with the ocean currents. 



This is a small matter when the flow of air in any one direction is of 

 short duration. But with the advent of September in central Canada and 

 the north central United States, the flow of air, when measured by weeks, 

 is predominantly from the northwest. There are periods of calm, days when 

 the warm autumn air moves up from the southeast; but when the whole 

 of the air movement from mid-September through November is measured 

 for any year, the major trend across the heart of the continent is from the 

 northwest (U.S. Weather Bureau, 1952) (Figure 26).* However far north- 

 ward the inexperienced juveniles may have wandered in August, the domi- 



° Although the dominant November flow of air over the main waterfowl breeding range is 

 from the northwest, the patterns of high- and low-pressure areas give some interesting variations. 

 Winds moving counterclockwise around the Aleutian low (Figure 26) create a westerly flow over 

 the Pacific Ocean from the Aleutian Islands to the continent; and there is evidence here ( such as 

 that presented by Yocom, 1947 ) of an oceanic migration of waterfowl and other northern birds in 

 autumn. The eastward flow of winds from the Greenland low suggests a reason behind the autumn 

 migration of Greenland birds toward Europe; and it may be with this same current that the Arctic 

 Tern takes its flight across the North Atlantic in the first leg of its long autumn migration. The 

 intercontinental flow of wind around the Aleutian and the Greenland lows may be the medium of 

 transportation by which North American waterfowl regularly drift to Siberia and to Europe. 



