Table 9.--Use of potholes by breeding pairs, 1950 to 1953 
[Based on 4,910 pair observations and 3,152 pothole 
observations. Includes the 391 potholes shown in table 3] 
Size class Pairs per acrel Average pairs per Pairs per wet 
(acres) acre, 1950-53 | acre, 1950 

0.0= 0.09 0 
O.l=- 0.3 8 
On4- 0.9 0 
1.0" 1.9 9 
2.0= 4.9 8 
5.0-11.9 7 
12+ 6 
All sizes 0.7 
‘Based on total acreage of size class even though some potholes of the size 
class are dry some of the time. 
Potholes larger than 2 acres were clearly the preferred early-season 
habitat for blue-winged teal and gadwall. The data for the mallard and pin- 
tail were inconclusive in that regard, as the main breeding population of these 
species had arrived before the beginning of spring work that year. Breeding 
populations of blue-winged teal and gadwall were low at that time, competition 
for space was not acute, and the use of small areas was insignificant. As the 
population built up, pairs became crowded and the use of small areas increased. 
These data also indicate that the populations responded quickly to fluctuations 
in water levels. An increase in the number of available potholes in the 
period May 23 - June 3 Was accompanied by a rise in the use by pintails of 
these small areas as the birds were able to distribute themselves more widely. 
A further rise June 4-13 in the number of areas available was accompanied by 
an increase in the use of small areas by pairs of mallard, gadwall, and blue- 
winged teal. Field observations in this and other years have detected a ten- 
dency in dry periods for the birds to congregate on larger potholes, making 
little use of the few small areas that remained. At those times, particularly 
June of 1950, the birds appeared to have lost interest in nesting. After a 
rain, when the number of potholes increased, the birds spread out over the 
countryside and could be seen on almost any puddle, making the greatest possible 
use of available space. This may possibly indicate a reduction in nesting 
activity during a period of overcrowding, followed by renewed interest when 
the birds could again spread out. 
There was considerable variation between species in their distribution 
throughout the potholes. Table 11 indicates that the diving ducks generally 
remained on large water areas, while the dabblers were much more dispersed, 
making most of the use of small areas. As shown in table 10, which deals with 
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