MIGRATIONS OF WATERFOWL 



The timing of this shift shows a remarkable consistency from year to 

 year. At Delta the first bands of postbreeding Mallard and Pintail drakes 

 are always seen by the tenth of May, the earliest large flocks by the end of 

 May, and dropped primary feathers, evidence of the first flightless drakes, 

 by the middle of June. At Whitewater Lake, Manitoba, Bossenmaier (1953a) 

 found only a week's difference between the gathering of the first flocks of 

 Mallard drakes in the very late spring of 1950 and that in the more normal 

 season of 1951. Baldpate and Green-winged Teal drakes regularly arrive at 

 Delta in mid-June, and the first cast primary feathers of Canvasback always 

 drift to the lakeshore in late July. Where nesting has been delayed by ad- 

 verse spring weather, however, there follows a delay in the peak of the 

 flightless period. 



We mark these events by the calendar, but the birds move on biological 

 time : the molt and the molting shifts are hinged to the sexual cycle. Drakes 

 of early-nesting hens are first to molt; males that breed later, molt later. So 

 it is that during the same week in May one may encounter some groups of 

 molting Mallard males, while other Mallard drakes, still paired, are in im- 

 maculate breeding dress. In some species, like Mallard and Pintail, the male 

 usually abandons his hen during the early stages of incubation. In others, 

 like Blue-winged Teal and Shoveler, the drake remains on his territory 

 through most or all of incubation, the postnuptial molt into the eclipse be- 

 ginning before the marital bond is broken. Although the molt into the 

 eclipse starts at about the same time as the hen commences incubation 

 (whether or not the male lingers on the territory nearby), there is yet no 

 complete understanding of the relation between the postnuptial molt and 

 reproductive activity. Seligmann and Shattock (1914) observed that the 

 "seasonal change of plumage in the Mallard is not connected with the sper- 

 matogenic function of the testicle," a decision recently confirmed by Hohn 

 (1947). 



The postnuptial molt into the drab eclipse plumage progresses gradu- 

 ally, the loss of the pinions and the flightless period of three to four weeks 

 coming as a climax ( Figure 19 ) . There is some individual variation in the 

 timing of the wing molt, however, and I found (Hochbaum, 1944a: 112) 

 that in old captive Canvasback drakes the flightless period arrived even 

 though there was not yet a complete change into the eclipse plumage. The 

 shift of molting drakes to the place where they pass the flightless stage is 

 likewise gradual. First there is a coming together by twos and threes, such 

 small bands being seen on the nesting range, the males presumably not far 



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