14 
Table 17. Percent nest success of canvasbacks adjusted for 
renesting in the Minnesoda study area, 1961-72. 




Initial Adjusted 
Year success SUCCESS 
196] 32 — 
1962 46 
1963 45 60 
1964 57 70 
1965 33 47 
1966 50 66 
1967 36 50 
1968 21 95 
1969 62 70 
1970 55 62 
197] 59 70 
1972 48 66 
Mean 45 59 

Table 18, Probable cause of canvasback nest losses in the 
Minnedosa study area, 1961-72. 

Nests destroyed 




Cause of losses No. Percent 
Raccoons 672 56 
Crows and red fox* 184 15 
Skunks 89 7 
Other mammals 106 9 
Flooded 72 6 
Deserted 76 6 
Burned 8 ] 
Total 1,207 100 


“Predominantly crow predation but both crows and foxes remove 
eggs from nests, 
vestigator disturbance occurred. Success of undisturbed 
nests was 50% and success of nests from which the hen was 
flushed at least once was 45%. Success of nests not occu- 
pied by the hen was only 28% , but some of these nests may 
have been deserted when found. It is apparent that flushing 
hens had little if any effect on overall nest success (X* 
3,286, P > 0,05). 
Clutch Size 
A total of 1,131 canvasback nests had completed clutches 
when they were found (Table 19). Clutch size for the 
12-year period average 7.7 eggs and ranged from a low of 
7,2 in 1970 to a high of 8.5 in 1968. Unparasitized nests 
(those not containing redhead eggs) contained larger can- 
vasback clutches than did parasitized ones. Average clutch 
size for nests not parasitized by redheads was 8.2. The 
average number of redhead eggs per canvasback nest was 
1.8 or 20% of the clutch. The average number of canvas- 
back eggs laid was 8.2 in the first nesting attempts and 6.9 
in renesting attempts, Clutch sizes of 497 unparasitized nests 
ranged from 2 to 16 eggs. Clutches larger than 12 or 13 
eggs may indicate that two or more canvasbacks laid eggs 
in one nest. 
The average number of canvasback and redhead eggs in 
successful canvasback nests was 9.5, whereas the number 
of canvasback eggs per successful nest was only 7.7. Of 
these, an average of 6.2 canvasback eggs hatched per nest. 
indicating an egg loss of 20% (Table 20), 
Nest Parasitism 
The percentage of canvasback nests with complete 
clutches that contained one or more redhead eggs averaged 
Table 19, Canvasback clutch data from the Minnedosa study area, 1961-72, 


Total eggs per nest 
Canvasback eggs per nest 


Complete 
Year clutches Canvasback Redhead Total Unparasitized Parasitized 
1961 58 7.4 2.1 9.5 8.1 6.8 
1962 91 7.7 1.8 9.5 8.2 Ya 
1963 96 7.9 1.8 9.4 7.9 7.2 
1964 108 7.6 2.0 9.6 5.6 7.0 
1965 104 7.9 2.3 10.3 &.9 7.6 
1966 103 8.2 1.8 10.0 8.7 7.5 
L967 96 7.3 2.7 10.0 7.6 7.2 
1968 SO 8.5 1A 9.9 5.5 5.0 
1969 109 8.2 1,2 9.4 §.2 7.7 
1970 86 7.2 18 9.0 7.8 6.6 
1971 107 7.3 1,7# 9.0 ta 6.8 
1972 93 7.5 1.9 9.4 8.1 tad 
Total or mean 1,131 7.7 L:9 9.6 8.2 7.3 



“Includes six ruddy duck eggs. 
