=< Ct 
15 
Table 20. Mean clutch data from successful canvasback nests in the Minnedosa study area, 1961-72. 


Canvasback eggs 

Eggs lost 



Total Total egus No. per No. hatched 
Year nests in nest! nest per nest No, Percent 
196] 2) 9.9) 7.6 6.8 0.8 1] 
1962 a4 Y.4 TA 6.8 1.1] 14 
1963 58 8.5 6.8 5.8 1.1 15 
164 G7 10.0 7.9 6.3 1.6 20) 
1965 60) 10.0 7.9 6.0 1.9 24 
L966 70 10.2 8.3 72 1.2 14 
L967 59 9.8 Td 5.4 1.8 25 
1968 30 10.0 8.2 5.6 Zt 32 
1969) 77 9.4 8.3 6.5 LS 21) 
1970 59) 8.8 7.2 9.6 1.7 23 
197] 79 S.8 7.3 8 1.5 2] 
1972 61 9.2 Td 6.3 1.1 15 
Mean ob 9.5 Ted 6.2 i) 20 


“Includes redhead eggs. 
57 for 1961-72 (Table 21). The average number of redhead 
eggs in parasitized nests was 3.14, Overall average number 
of redhead eggs hatched in parasitized canvasback nests was 
0). 64, 
Redheads arrived and began nesting in the Minnedosa 
area about 2 weeks later than canvasbacks (Appendix B). 
Redhead first-nesting peaks coincided with renesting efforts 
of eanvasbacks. More canvasback renests were parasitized 
by redheads than first nests (paired ¢-test, P < 0.05; Table 
22). There appeared to be a positive relation between levels 
of nest parasitism by redheads and sizes of their breeding 
populations. 
Table 21. Average number of redhead eggs in parasitized 
cancasback nests in the Minnedosa study area, L961 —72, 


p bus No. redhead eggs in nests 
ercentage) ————— 



of nests Successful Failed Hatched 
Year parasitized nests nests per nest 
LOG] 53 1.9 4.0 (.5 
1962 55 3.2 3, 0.5 
1963 O7 2.6 3.1 0.6 
106-4 96 3.7 3.4 0.6 
1965 TO 3.0 3.6 0.6 
1966 56 3.2 3.3 0.9 
LOGT 64 3.8 5.0 (7 
L968 4] 3.1 3.6 0.5 
1960 42 2.5 3.0) 0.5 
L970 42 3.2 4.2 0.8 
1971 60) 3,1 3.1 OS 
1972 a4 L.7 2.2 0.6 
Total nests — 1,174 946 — 
Moan 57 3.1 3.0 0.6 
WNests that contained at least one redhead egg. 
bThese figures may be low because identification of egys was 
impossible in some hatched nests. 
Nesting Habitat 
The number and success of canvasback nests by habitat 
types within the intensive study unit are presented in Table 
23. Wetland sizes used in these tables are the same as those 
used in May habitat surveys (Tables 1-7). 
Of the total canvasback nests, 94% 
Types 4 and 5, and nest density was greatest in Type 4. 
These relations probably reflect the relative availability of 
suitable nest cover among the various wetland types. Nest 
success did not differ significantly in wetlands of Types 3, 
4. and 5 (X? = 0,225, P > 0.05). 
Of all nests, 41% occurred in wetlands of 0,2 ha or less 
and 65% in wetlands of 0.4 ha or less (Fig. 10). Areas of 
many of these wetlands were less than 0.5 ha, About 2% 
were in wetland 
of the nests found were in wetlands larger than 2 ha. During 
Table 22. Redhead parasitism of canvasback nests, by 
nesting attempt in the Minnedosa study area, 1964-72. 

First nesting Renesting 


Canvasback Redhead Canvasback Redhead 
nests egys/ nests egys/ 
parasitized canvasback parasitized canvasback 
Your (%) nest (%) nest 
1964 49 2.7 70 4.5 
L965 4] 1.3 78 2,7 
L966 os 1.6 ot 2.1 
L967 56 9,2 7A 3.4 
1968 33 1.0 08 21 
1969 48 1.3 35 1.2 
L970 40 I 54 2.0 
1971 58 1.6 68 2.2 
1972 53 1.3 095 1.9 
Mean 48 1.6 6] 2.5 



