
100 Percent of potholes with 100 
water on May 10 
80 80 
60 60 
hO 4O 
reeding pairs per square mile 
20 20 
0 ) 

1950 1951 1952 1953 
Figure 23.--AVATLABLE WATER AREAS AND DUCK BREEDING POPULATIONS, 1950-53. 
in the spring and the size of the breeding population for the four years of 
the study. These variations in numbers of water areas are, of course, the. 
result of varying degrees of drought, but drought parallels the present-day 
pattern of drainage (that is, the smaller more temporary potholes are the 
first to go dry and the first to be drained, followed by those next in order 
of permanence). 
52 
