39 
All but three types, A2, B3, and Bl, were used extensively, types Al and D 
most heavily by dabblers, while d‘ving ducks were found exclusively in Types Al 
and A3. The lack of use of Types B3 and Bh is probably not significant since no 
potholes of the former and only two of the latter types were sampled. The others 
were either dry or outside the boundaries of the area as it was first established. 
The low use of Type A2 suggests that the dense cattail surrounding these areas 
may have restricted visibility to the extent that birds did not feel secure in them. 
Table 20 shows the percentage of potholes occupied by breeding pairs during 
this period. Types A3 and D were the most heavily used (100 percent of each 
occupied) while Types Al and Al, follow with 78 percent and 71 percent. 
Table 20. Percent occupancy by type (breeding pairs). 


Type Number of potholes Percent 
sampled occupied 
Ws 
A2 5 20 
A3 3 100 
AL 7 71 
Bl 26 42 
R2 5 40 
B3 0 0 
Bh 2 0 
Cc 6 67 
D a 100 
Total 75 57 

Size Preference -- Table 21 shows the size of potholes used most heavily by 
breeding birds. In order to rule out the effects of cover types, only the Type 
Al and Bl potholes were considered. 
Table 21. Influence of pothole size on use by breeding pairs 
(4 Types Al and Bl potholes). 
Pothole size Number of Pairs per acre 
(acres) potholes ver ducks Diving ducks 
e oa e e 0 
0.5 = 0.99 12 Ty. 0 
1.0 ~ 1.9 6 1.5 0 
1.5 = 1.99 5 0.9 0 
2.0 - 2.99 3 0.3 OW 
3.0 - 3.99 3 0.6 Own 

Dabbling ducks in terms of pairs per acre of pothole made the greatest use of 
the 0.0 to 0.5 acre areas, while the diving duck curve starts at the 2 to 3 acre 
size class, There is a decrease in intensity of use by breeding river ducks with 
increase in size of the area. This phenomenon has already been discussed by Stoudt 
(in Williams 1919) and by Hochbaum (19),) who has shown that the number of pairs 
occupying an area is dependent upon the length of shoreline, which increases only 
as the square root of the area. 
The heavy use of Type A3 by diving ducks (Plate XVIII) may be caused more by 
the large size of those areas than by their cover type; comparison of Plate XVIII 
and Table 21 with Tables 8 and 11, showing the use made of the pothole types by 
broods, shows that the breeding birds were affected more by the size of the area 
and less by its cover type than were broods. . 
