SEASONAL FLIGHT OF DUCKS 191 



winter in the Mississippi River drainage, and then 

 flew north in spring through the interior. The 

 northward flight in spring through the Mississippi 

 Valley is much more abundant than the southward 

 movement through the same region, indicating that 

 birds come in converging lines to favorable winter- 

 ing grounds, where they concentrate, and then travel 

 north in company. It is possible that the difference 

 in spring and fall movement in this area is more ap- 

 parent than real, since we find in autumn, through 

 the Plains area in particular, that water is scarce, as 

 that season of the year is usually dry. This would 

 force waterbirds to drive on through without stop- 

 ping, while in spring, after the rains and snows of 

 winter, every pond and slough is filled with water 

 and offers attractive feeding grounds. On rare oc- 

 casions when early autumn rains fill the marshes 

 which normally at that season are dry, the increase 

 in ducks in southward flight is very noticeable. 

 These birds undoubtedly have what may be termed 

 "weather sense," which draws them to follow shift- 

 ing seasons that offer conditions in their favor. In 

 late December, 1920, 1 was engaged in field observa- 

 tion in the western pampas of Argentina, in a region 

 where no rain had fallen in months, and where 

 lagoons and marshes were entirely dry. One even- 

 ing there came a tremendous downpour of rain, a 

 veritable flood, and on the following morning I 



