
20 



4 
: = wv? dp “ = ; - 1+. 
oe ee . ’ 
= ; ‘e- : | . 
ne vs Pn we Se PORE pai oe 
panes. “bh Be Ba 2 , 
olay hares Me" ss a TOS tet ho 
yh 
byte ' . 4 
¥ : RS PRRs 
y ' =A 
. é . . ’ 
+ . 4 ce. ai ol ; 6. dean 
ih eA S f c py: VW fy ‘ , 40%) 4 
iba wr a 4, it, 4 ‘ " 5 ‘ we « 
Vi i y t yd “ aS ' ore 
ra ' ¥ 4 4 " ;" 
ert} iA be ie 44% ¥ 6 - ‘ ‘af 
‘ oe 5 kha ae Lr a AS she ie. uf wba malts 
Fig, 11, Canvasback brood in a small wetland in the Minnedosa study area. 
cause the number of breeding pairs was small, Nest suc- 
cess was poor in 1965 but production was only slightly 
below average because the breeding population was high, 
The poorest production — in 1968 —was caused mainly by 
poor nesting success. Production was highest in 1964, when 
the breeding population and nesting success were both high. 
Good production in 1963, 1966, and 1969 was mainly a 
result of a high rate of successful nesting. 
Dzubin’s (1952;:73, 1955:88) reports on the Roseneath 
study area permit a comparison of brood data from cer- 
tain other vears. The numbers of broods found averaged 
3.39 + 0.45/km? during 1949-55, as compared with 1.86 + 
0.77 on the same area in 1962-67. Although the number 
of broods produced were 0.54/km2 lower during 1962-67, 
these differences were not significant (f = 1.46, P > 0,05), 
Broods per nesting pair during 1949-55, however. were 0.88 
+ ().24 as calculated from Dzubin’s data (1952:73, 1955:S8) 
compared with 0.48 + 0.14 brood per pair on the same 
area from 1962 to 1967, These results showed significantly 
lower productivity (¢ = 2.29, P < 0,10). Productivity 
(broods per pair) on three study areas from 1961 to 1967 
was 0.7 for Redvers, Saskatchewan (Stoudt 1971), 0.6 for 
Lousana, Alberta (Smith 1971), and 0.4 for Minnedosa, 
Manitoba (present study). The lower rate of production at 
Minnedosa in recent years can probably be attributed to 
raccoon predation, 
Reproductive success of canvasbacks on the intensive 
study area was measured by nest studies and the number 
of pairs per brood. Average productivity was 37% by the 
pair-brood method and 53.3% by the nest success method 
(Table 32). The difference between the two may be a 
measure of brood movement off the roadside transects, mor- 
tality of entire broods, or failure of some hens to nest, 
Estimated annual production of canvasback ducklings 
