2 
IX. DISCUSSION 
It has been demonstrated in this report that waterfowl broods are able to adjust 
themselves to varying conditions of habitat such as occurred in 199 on the Minnedosa 
area. 
Interspersion of Pothole Types 
Owing to their high mobility, waterfowl are well able to make free use of 
various pothole types. Plate XIX summarizes the use of the various types by the 
three most critical phases of the breeding cycle and serves to point out the 
importance of considering the interspersion of the various types. Semipermanent 
cattall potholes were particularly conspicuous in having the highest percent acreage- 
use value fordiving-duck nests, but very low values for other functions. Permanent 
sedge-white top potholes, on the other hand, had little importance for nesting but 
a high rating for breeding pairs and broods. The only type providing a balanced 
habitat was “Permanent bulrush" which was heavily used by all three phases. We 
feel certain that temporary waters were undervalued in the study of their use by 
breeding pairs owing to the late date at which field work was begun. 
The data indicate that a region which contains a well-balanced mixture of the 
various types is highly desirable, To achieve maximum production, this should 
certainly include enough permanent areas, preferably sedge white-top and bulrush to 
assure sufficient rearing cover. Without sufficient nesting cover in the form of | 
cattail and bulrush, apparently preferred when found in small, semipermanent pot- 
holes, it is doubtful whether many diving-duck broods would be hatched. The sama 
conclusion would apply to suitable upland cover for river-duck nesting. Finally, 
without sufficiently dispersed breeding territories provided by a large number of 
semipermanent and temporary potholes, there would be few pairs resident in the 
region and few nesting attempts. 
The above discussion points out the importance of considering this type of 
habitat as a complex of potholes each having one or more functions in the produc- 
tion of waterfowl but each in turn dependent on its proximity to other potholes 
which can better serve other functions. To regard each individual pothole as a 
complete production unit seems illogical if we consider the fact that a pair of 
canvasback resting on it in the spring may have a nest in an entirely different 
type some distance removed, and may depend on a third type for brood rearing. 
None of these potholes should be considered as having produced a canvasback brood, 
but each was essential to its production even though it might function for only a 
very short time; rather, theregion produced the brood, Thus any consideration of 
this type of habitat must be based on a unit of land rather than the individual 
pothole, 
In habitat such as the Minnedosa study area, where the potholes are small and 
closely intermingled, it appears that the square mile is a good unit for consider- 
ation. The many small transient areas furnish breeding territories for a large 
number of pairs while there are mumerous potholes suitable for the other phases 
of the breeding cycle as has been discussed. There was considerable upland cover 
for river-duck nesting and considerable cattail and bulrush in both permanent and 
semipermanent potholes for diving-duck nesting. Several areas were used by post- 
breeding birds and flying young and there were apparently more than enough waters 
favorable for brood rearing. Finally, all of these factors essential to the repro- 
duction of the species present were contained in an area which was well within the 
limits of mobility of the species since both adults and young could easily traverse 
it. 
