Figure 10. Standard direction of mass fall migration from Whitewater Lake, Lake Mani- 

 toba, and Lake Winnipeg marshes. The standard direction from the Delta Marsh is 

 followed by all ducks, holds the same year after year, and is constant regardless of wind 

 direction. Stippled area shows the Pre-Cambrian Shield. 



taining their maximum intensity near sundown. The outstanding feature of 

 such avalanches is the uniformity of direction. At Delta, the migrants arrive 

 from the northwest and depart into the southeast. On any given day all 

 flocks and all species go this way, the direction is maintained every day of 

 migration, and the same course is held each year, so that in 1954 the pas- 



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