74 
The calculated ratio of brood per pair was .45. A figure somewhat 
lower than that obtained by Evans in 1949. This figure may have been altered 
by a marked egress of broods from the area, due to the abnormally dry year or 
by an incorrect census of the early flying mallard and pintail broods. 
Agricultural Influences 
Spring burning of stubble was general in the district surrounding the 
study area. Due to last year's wet fall, farmers found it more convenient to 
burn their stubble this spring. A search of four quarter sections of burned 
wheat and barley stubble revealed destroyed mallard and pintail nests. Birds 
appeared to be somewhat reluctant to nest in stubble which was over 100 yards 
from water; but they did utilize stubble which was adjacent to the grasslands 
around potholes. The dried grass edge around potholes and the shrubbery around 
the aspen bluffs constituted the best available nesting cover for dabblers. However, 
it readily caught fire when stubble was burned and thus many nests were destroyed. 
Crows would generally seek out burning fields and feed upon the exposed nests. 
Spring cultivating of unburned stubble exposed many nests, especially 
those near the adjacent pothole grasslands. Farmers as a rule, moved nests out 
of the way of their machinery. However, few, if any of these nests hatched 
successfully, because they were readily destroy2d by crows and other predators. 
Water Conditions 
Spring runoff in the immediate vicinity of the study area was much lower 
than that of the previous year. Light winter snows and lighter spring rains added 
very little water to potholes. Of 146 potholes on the area, only 41 showed a depth 
increase over a reading taken on September 5, 1951. Abnormally high April and 
May temperatures soon dried out many of the temporary water areas and reduced 
depths in all others. Weekly readings of water gauges in all potholes in the area 
showed an almost continual drying trend through the summer months. The decrease 
of water depth due to evaporation appzared greater in smaller potholes. The 
accompanying graph gives some indication of the number of potholes which were 
dry at weekly periods during the time of the study. 
Note that between June 17 and July 1 (see graph), 14 water areas which 
were previously dry, again became partially filled with runoff rain water. Rainfall 
during this 2-week period was 1.75 inches and the water level of all potholes was 
raised anywhere from .5 to 4.25 inches. It was noted that potholes which had 
previously gone dry did not hold much runoff rain water. This may have been due 
to drying and cracking of the mud forming the bottom stratum, which in turn 
affected the capacity of the depression to trap water. 
Rainfall played a very important part in regulating water levels. It reduced 
evaporation to a minimum and, if heavy enough, added some water to the potholes 
with large drainage basins. In the latter case, heavy thunder showers added more 
water to potholes than did a daylong drizzly rain. Certain potholes near Minnedosa 
which were examined by Kiel and myself, had added as much as eight inches of water 
after a heavy 20-minute thunder shower. However, such occurrences are very rare 
and localized. 
