
contained water, while on the same date in 1952, owing to heavy February 
snows and rapid spring runoff there were nearly 350. These conditions are 
briefly expressed for the four years of study in table 4. It should be 
noted that pothole depths followed this same general trend for the four years 
of the study. 
Table 4.--Relative abundance of potholes on Waubay study area, 1950-53 
Growing season 
precipitation 

Pothole abundance 
before June 1 after June 1 

average 














fewest 
1950 average. medium fewest 
1951 high . Tewest medium medium 
1952 low most medium medium 
very high medium most most 


Much of this variability is due to factors not related to the actual 
amount of precipitation. It is dependent to a large extent on the character 
of the spring runoff, which is highest when the breakup comes quickly and the 
ground is frozen so that none of the water penetrates the soil. Under these 
conditions, even a moderate snowfall will put considerable amounts of water in 
the potholes. If this is followed by average rainfall throughout the season 
in the form of fairly hard showers, good supply of surface water is assured. 
Forty-one potholes on the study area went dry only one year out of the 
three and may be used to illustrate the variability of runoff. It would be 
expected that all of these would have gone dry in 1950 when average water 
levels were their lowest. However, only 26 of the 41 went dry that year, while 
the remaining 15 went dry only in 1952, a much wetter year on the average. 
Moreover, six of the areas that went dry only in 1952 lie immediately adjacent 
to potholes that went dry only in 1950, indicating that local differences in 
weather could not be a factor. The differences are due to the character of the 
individual watersheds as they influence runoff from rain or from melting of 
drifted snow. 
None of the potholes on the study area are permanent enough to survive a 
prolonged drought. For example, during the drought of the thirties every pot- 
hole on the study area went dry and most, even some of the most permanent, were 
capable of bearing crops. 
DUCK POPULATIONS 
opring migrants 
Karly trips in 1951 and 1952 indicated that spring migrants do not use 
this area to any great extent. The spring breakup in this relatively high 
country is somewhat later than in the Minnesota and James River Valleys which 
are major spring-migration channels. The majority of the birds seen-on the 
study area, even in early April, were in scattered pairs and appeared to be 
settled down preparing to nest. The exceptions were provided by a few scattered 
groups rarely amounting to more than 100 individuals. During the four years of 
the study, local breeding populations apparently branched from the main routes 
20 
