13 
Table 15. Nesting success of canvasbacks in the Minnedosa District, 1961-72. 

Number of nests 




Percent 
Year Found Active Usable# Failed Hatched successful 
1961 102 90 90 61 29 32 
1962 185 156 134 73 61 46 
1963 238 196 180 99 §1 45 
1964 227 187 156 67 89 o7 
1965 298 207 198 133 65 33 
1966 232 181 173 87 86 50 
1967 252 192 179 115 64 36 
1968 253 159 152 120 32 21 
1969 203 163 162 62 100 62 
1970 177 148 141 64 ee 55 
1971 175 160 153 63 90 59 
1972 169 146 140 73 67 48 
Total 2,511 1,985 1,858 1,017 841 45 


‘Nests deserted due to disturbance by the searching crew were not included in calculations of nest success, 
brood count was only 21; thus presumably not more than 
6 broods were produced by the second nesting attempt. 
Since nest success from the late nesting effort was 55% , 11 
(65 % ) of the 17 remaining hens must have renested, Age 
classes among the 21 broods found during counts on 21-23 
July were used to check accuracy of these calculations. Since 
15 broods should have come from the early nesting effort, 
they should have been of age class Ic or older, and the re- 
maining 6 should have been in classes Ia and Ib. The actual 
count of broods was five Ila. four IIb, and six Ic, plus two 
la and four Ib. 
Nest data for the entire area showed that, for first 
attempts, 115 hens produced 54 broods. Of the 61 remain- 
ing hens, 65% produced 22 broods. Total production in- 
cluding renesting was 76 broods and thus the adjusted nest 
success for 115 hens was 66%. 
This adjusted nest success was considerably higher than 
the uncorrected nest success of 50% , and probably repre- 
sented a value closer to the truth. Canvasback nest success 
adjusted for renesting in the Minnedosa area for other years 
of the study showed a 24% increase over the initial data 
which represents the effect of renesting (Table 17). 
Nest Losses 
Predation accounted for 86% of the nest losses and 
flooding, desertion, and burning for the rest (Table 18). 
Raccoons destroyed 64% of the nests lost to predators. 
During the 12-year period, 547 nests were observed 
without the hens being flushed. Inasmuch as these nests 
were not checked until after the eggs had hatched, no in- 
Table 16. Nest success of canvasbacks by areas in the Minnedosa District, 1963-72. 



Area 


Minnedosa—Shoal Lake 
South of Minnedosa 
Minnedosa—Strathclair Strathelair-Shoal Lake 








Destroyed Destroyed Destroyed Destroyed 
by by by by 
Nest Success raccoon Nest Success raccoon Nest Success raccoon Nest Success raccoon 
Year (no.) (‘%) (‘%) (no.) (%) (%) (no.) ( %) (%) (no. ) (%) (% 
1963 180 45 37 116 43 29 38 9 35 57 7 
1964 156 57 AT 11] ov 33 23 43 9 22 72 5 
1965 198 33 74 148 28 19 26 7 31 61 6 
1966 173 50 40 14] 49 12 58 0 20 50 6 
1967 179 36 69 134 28 56 20 45 g 25 68 4 
1968 152 21 70 98 7 60 25 28 7 29 62 3 
1969 162 62 33 108 56 26 22 50 5 32 88 9 
1970 14] 55 35 101 46 32 9 78 ] 31 71 2 
1971 153 59 29 112 57 26 10 70 ] 3l 61 2 
1972 140 48 47 115 44 43 § 50 3 17 76 ] 
Mean 163 46 50 118 42 18 49 5 27 67 4 


