
26 
es 
Fo <>" eo 
a ee ee ee, Soe ee 
ee ™ ye 4 — --r4, —s 
EE 2 tie Ss 
* Me 

Fig. 16. Wetland drainage and fall plowing in the Minnedosa study area. 
(1964:36) reported a 10% success rate for 67 canvasback 
nests. It was 37 % in 1960 and 19% in 1961. Drought con- 
tributed to the rate of nest destruction in 1959 and 1960 
because nests were stranded on dry ground before hatch- 
ing, which rendered them available to all upland predators. 
including raccoons. 
The 1968 nesting season provided some noteworthy in- 
formation on predator adaptability. As the nesting season 
progressed, a combination of receding water levels and ex- 
tensive burning contributed to a greater-than-normal toll 
by predators. Increased predation also occurred on other 
species of upland nesting ducks. indicating a shortage of 
predator food, This shortage was emphasized by the fact 
that certain predators such as red fox. skunks, and feral cats, 
which normally do not enter the water while hunting, were 
wading in the water more than 30 em deep to search for 
overwater nests. Raccoons were also more destructive than 
ever and many wetlands were so thoroughly searched by 
these predators that not a single intact duck, coot, or black- 
bird nest could be found. Data from 98 nests found in 1968 
on the intensive study area indicated nest success of only 
8% . the lowest ever recorded for canvasbacks. 
Nest studies were also conducted west of Minnedosa for 
a distance of about 64 km. Raccoon populations appeared 
to be lower west of the Minnedosa River Valley and less 
burning was done in that area, Both of these deterrents to 
nest success diminished consistently farther away from the 
river valley. Canvasback nest success apparently reflected 
this trend in 1968, Eggs hatched in only 7% of the nests 
south of Minnedosa,. 40% between Basswood and Newdale. 
and 62% in the vicinity of Shoal Lake. 
Basswood, Newdale, and Shoal Lake are 16, 32. and 
64 km northwest of Minnedosa, respectively. This disparity 
between nest success south of Minnedosa and that northwest 
