FLIGHT TRAILS SOUTH 



through, as already described; sometimes they stopped, especially if the 

 storm was severe, leaving hunters to believe that it was the bad weather that 

 forced them south. When travelers choose to continue on in spite of the bad 

 weather they may have overtaken, their flights usually carry them through 

 to some more southern marsh. But the migrants by no means always attain 

 their destination, and sometimes vast numbers of waterfowl perish when 

 forced to ground by bad weather. ( See Chapter 12. ) 



A study of the movements of waterfowl through the autumn reveals that 

 ducks select anticyclonic weather for the start of their mass migrations, but 

 that the weather is not in itself the impetus. In September Mallards do not 

 always migrate with the favorable barometric situation that has a "trigger 

 effect" on Blue-winged Teal. Most Lesser Scaups and Mallards remain at 

 Delta through a mid-October anticyclone during which Redheads and Can- 

 vasbacks vacate the country. In the September and October movements 

 there is a falling temperature, but this may not even come close to freezing; 

 and both Blue-winged Teal and Canvasbacks leave a span of fair weather 

 and an abundance of food behind when they go. And while the November 

 migration of Lesser Scaups and Mallards coincides with the freeze-up, hard 

 weather and ice are not in themselves the cause of migration. Some years 

 large numbers of Mallards remain north in mild Novembers and then fail 

 to migrate southward when the inevitable deep cold of December and Janu- 

 ary arrives, sometimes perishing with open water only a few hundred miles 

 south (Rowan, 1931). 



The schedule of the autumn migration is a confusing puzzle, beginning 

 as it does in August and continuing until November. But when the differ- 

 ent sex and age groups are studied individually * we find that there is an ar- 

 rangement of order. At Delta the fall movements have a remarkable regu- 

 larity from year to year, the exceptions being traceable to extreme weather 

 variations, drastic water-level changes and late breeding seasons. First to 

 go in mid- August are the adult drake Pintails ; most of them are on the wing 

 (after the flightless period of the eclipse molt) by early August and have 

 departed from Delta by the end of the second or third week of that month. 

 Following close behind are the adult male Baldpates; so common as flight- 

 less molters in midsummer, they move away from Delta in late August or 

 early September and are uncommon for the balance of the autumn. At 



•The study of autumn movements has been greatly enhanced by the opportunities of 

 examining large numbers of waterfowl in banding traps and in hunters' bags along the stopping 

 places of migration and by the possibility of making completely objective appraisals of the sex 

 and age composition of these samples (Hochbaum, 1942; Elder, 1946). 



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