Land use, particularly grazing intense enough to completely remove the 
plant cover, may render unsuited to brood use some of the smaller, shallower 
potholes which might otherwise be used. Human interference such as continual 
activity, even of a violent nature, such as a brood beatout, does not diminish 
use except for the occasional brood driven ashore during the actual beatout. 
Even that brood is likely to return once the activity has subsided. 
Flightless adults 
Moulting ducks on the study area were a rarity, and none were seen until 
1952 when three flightless hens were found in deep marshes. It appears that 
there is not ordinarily deep enough water in the emergent vegetation on pot- 
holes of sufficient size to satisfy the needs of birds in this condition. 
Whatever the cause, potholes on the study area were of no importance in this 
regard. 
Flying juveniles and fall migrants 
Flying juveniles and fall migrants made heaviest use of the larger pot- 
holes, generally deep marshes or open-water areas. Gadwall, baldpate, blue- 
winged teal, and shoveller showed preference for open water, while pintails 
favored areas with more cover and mallards were intermediate. There were too 
few diving ducks present in late summer and fall to indicate preference. 
Selection of habitat by all species at that time was extremely haphazard and 
seemed to depend as much on a flocking tendency as on other factors. At this 
season, food was an important consideration, and gatherings might often be 
found in areas where there were beds of arrowhead or pondweeds. - 
With the advent of the hunting season, many ducks were driven off the 
“large open potholes. Such mallards and pintails as did not leave the region 
entirely were often found in the deep marshes. There they were seldom dis- 
turbed; no hunters were seen "jump shooting" these overgrown areas. 
The changing needs of the ducks were well adapted to the seasonal vari- 
ations in the habitat. Breeding pairs seeking isolation could find it in the 
abundant small depressions filled by melted snow and spring rains. During the 
early part of the nesting season, most areas had little cover, as all but the 
toughest vegetation had been beaten down during the winter. Later, in June, 
when the broods were hatching, many of the temporary areas and shallow marshes 
were dry, but by then the desire for dispersal had decreased and the birds 
could freely move into the larger more permanent areas. They were then more 
concerned with the shelter provided by the season's new growth of vegetation. 
In the course of even one breeding season, a pothole that did not play some 
part in duck production was a rarity; in the course of several years of 
varying climatic conditions, every depression capable of holding water on the 
Waubay study area was used by ducks and, because of that use, probably has a 
value in duck production. 
43 
