MIGRATIONS OF WATERFOWL 



the month and until May 4, it moved well south of Delta. On May 4 the 

 front retreated rapidly northward, and on the following days the Arctic 

 air was pushed beyond the northern boundary of Manitoba. Between April 

 10 and May 4 there was very little migration of waterfowl or other birds 

 northward from Delta. There were some massive arrivals from the south, as 

 on the morning of April 13; and there were times when scattered flocks, 

 especially of hawks, blackbirds, and Crows, were seen moving northwest 

 against hard winds. But the whole period was one when there were no great 

 movements of any kind away from Delta, when scattered travelers were 

 seen only in small numbers. Through this period of Arctic air dominance, 

 there was much north wind; the weather was stormy, with occasional rain 

 and snow squalls. But there were also fine days of blue sky, rising tempera- 

 tures, and little or no wind. During such fair periods we watched for a 

 northward movement of ducks, but none passed through. Waterfowl re- 

 mained in their great concentrations on the marsh and on the flooded fields 

 in such numbers and so much later than usual that it was the subject of 

 much comment by local farmers and sportsmen. With the retreat of the Arc- 

 tic air on May 4, however, there began an avalanche of northbound water- 

 fowl and many other travelers, the first heavy passage we had seen since 

 April 9. 



What did these waterfowl perceive in the weather that inhibited their 

 northward travel during the fine days between April 10 and May 4? Had 

 they gone north of Delta in April, they would soon have reached country 

 still in the grip of frost. Surely on April's bright days they must have been 

 aware of some subtile character in the local weather that discouraged their 

 migration into the frigid region beyond. 



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