WINNIPEG ^370 Ml.- MINNEAPOLIS —340 Ml.— PEORIA' — 380 Ml. • MEMPHIS ^ 330 Ml. ^ BATON ROUGE 



NOV. I 



Fig. 9.— Hourly temperatures reported by weather stations at Winnipeg, Minneapolis, Peoria, Memphis, and Baton Rouge 

 on the day before and the day on which the mass waterfowl migration of 1955 passed through the region of each of these 

 cities; also the hours of greatest migration (indicated by heavy horizontal line) in each area, as interpolated from field 

 reports. 



while, on October 24, the average temperature was 30.8 

 degrees and the minimum was 16.6 degrees. 



It is apparent that the minimum tempeeature on 

 October 24 did not affect waterfowl migration to the ex- 

 tent a higher minimum did on November 1. It appears 

 that the cumulative effect of the cold was more im- 

 portant in initiating migration than a single sharp drop 

 in temperature. 



Fig. 9 shows the hourly temperatures reported by 

 five weather stations on the day before and the day on 

 which the mass waterfowl migration of 1955 passed 

 •through the region of each of these stations. The sta- 

 tions were spaced almost equidistantly along the line 

 of migration. 



It is apparent that the mass waterfowl migration 

 was well underway at Winnipeg, Manitoba, before the 

 Continental Arctic air mass began to depress the local 

 temperature at hour 15 on October 31. By hour 24, the 

 temperature had dropped 10 degrees below the minimum 

 of the previous day. 



The front of Continental Arctic air pivoted around 

 the low pressure area centered in southwestern Mani- 

 toba to swing eastward, thereby dropping the tempera- 

 ture at Minneapolis, Minnesota, at almost the same time 

 as at Winnipeg. At Minneapolis the waterfowl flight 

 arrived with the mass of Continental Arctic air, which 



dropped the temperature 7 degrees below the minimum 

 of the previous day. 



The main body of the waterfowl flight arrived at 

 Peoria, Illinois, in advance of the mass of Continental 

 Arctic air, which commenced to drop temperatures there 

 at 1 P.M., November 2. Temperatures fell 17-20 degrees 

 below minimum temperatures of the previous afternoon 

 and night. 



At Memphis, Tennessee, part of the main body of 

 the waterfowl flight arrived before and part with the 

 mass of Continental Arctic and Polar air, which 

 dropped temperatures 22-24 degrees below minimum 

 temperatures of the previous evening and night. 



The .Arctic and Polar air mass arrived at Baton 

 Rouge, Louisiana, during the early morning of Novem- 

 ber 3, dropping the minimum temperature 10 degrees. 

 Arrival of the waterfowl flight was concomitant with 

 arrival of the cold air. 



Precipitation. --When snow covers waste grain in 

 harvested fields to the extent that it makes for diffi- 

 culty in the feeding activities of mallards and pintails, 

 an exodus of these species may occur. The extent of 

 the exodus depends usually upon the depth of the snow. 

 The small amount of snow that had fallen on the Great 

 Plains of Canada by November 1 was not sufficient in 

 itself to account for the mass departure of mallards and 



23 



