MIGRATIONS OF WATERFOWL 

 wind favors the movement of most ducks going to the northwest, the Blue 

 and Lesser Snow Geese travel to the northeast, directly across the main flow 

 of air. Clarke (1912) believed that the clear weather of the high-pressure 

 configuration influenced the start of heavy migrations, but that the wind 

 produced by this barometric arrangement did not control the direction of 

 migration. We must examine other qualities of the anticyclone that influ- 

 ence migrations. In this respect, we have noticed that among the captive 

 birds at Delta, during their winter residence in the indoor pens, there is 

 increased activity — of feeding, fighting, wing-beating and courtship — when 

 the weather changes from "low" to "high," this despite the fact that they 

 are protected from the wind. 



Lowery (1951:468) points out that "since the general movement of the 

 air is from the high-pressure area toward a low-pressure area, birds starting 

 their migrations with favorable tail winds are often ultimately carried to a 

 region where conditions are decidedly less favorable. In the vicinity of an 

 area of low pressure the greater turbulence and high wind velocities, com- 

 bined with the possibly slightly less bouyant property of the air, caused 

 birds to descend. Since low-pressure areas in spring generally precede cold 

 fronts, with an attending shift of wind to the north, an additional barrier 

 to the northward migration of birds is imposed." Very often we see this 

 effect on the travelers at Delta. All morning there may be a steady flow of 

 Juncos, blackbirds, and many others past my office window; then suddenly 

 I am aware that travel has stopped. Great flocks of Juncos are feeding every- 

 where on the lawn and about the hatchery; the taller trees are loaded with 

 blackbirds and the thickets with Robins, Tree Sparrows, and other small 

 birds, many of which now burst forth in song. A cold, damp wind comes in 

 off the lake, the long cloudline of the front passes overhead, and we know 

 that the heavy passage has stopped for a while. 



The westward direction of the movement along the lakeshore at Delta 

 is standard except when (as occurs at least once each year) these migrants 

 turn about to fly steadily in the direction whence they came. I take this to 

 be a reverse migration, such as is described by Natorp ( 1932 ) , Lewis ( 1939 ) , 

 and others. Such reverses seem to be associated with sharp changes in the 

 weather pattern. On the morning of April 21, 1951, for example, there was a 

 southeast wind of 5 m.p.h. ; the sky was lightly overcast, the temperature, 

 38° F. From 5:30 to 7:00 a.m. there passed a steady westward flight of black- 

 birds, mostly Redwings, which at its peak averaged a flock a minute. This 

 traffic slowed down shortly after 7:00, after which single flocks went by at 



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