
10 
Table 6. Mean yearly number and area of May wetlands 
on transects, by dominant emergent vegetation, in the 
Minnedosa study area, 1962-72. 



Number Area (ha) 
Dominant emergent 
vegetation Mean Per km? Mean Per km? 
None 395 7.7 142.6 2.8 
Whitetop 357 7.0 83.8 1.6 
Cattail 206 3.9 96.4 10 
Mixed@ 254 5.0 161.6 al 
Bulrush> 107 1.9 117.1 2.3 
Willows 36 0.8 5.7 0.2 
Total 1,355 26.3 606.7 11.7 

aMixture of bulrush, cattail, and whitetop. 
bMainly hardstem bulrush, 
1972. the number and size of wetlands containing white- 
top were reduced considerably by high water. Hardstem 
bulrush was also plentiful. Wetlands with dense stands of 
bulrush along the shoreline were typical, especially early 
in the season before the emergence of whitetop, when resid- 
ual bulrush remained from the previous season. 
Less than 10% of the surface of 61% of the ponds was 
covered by emergents in early May (Table 7). The larger 
wetlands were usually the deeper, and the fringe of emer- 
gent plants was usually narrower than in the smaller wet- 
lands. 
Water Levels 
Mean water levels were 66 cm higher in 1972 than in 
1962. Both water levels and numbers of wetlands decreased 
markedly in 1968, apparently because precipitation was be- 
low normal in both 1966 and 1967. A 13,5-cm deficiency 
in rainfall occurred during the last 8 months of 1967, 
The poor relation between wetland numbers and water 
levels in 1971 and 1972 was caused by extremely high water, 
which often resulted in the joining of two or more ponds 
into a single body of water. Several residents in the area 
stated that water levels in 1972 were the highest they could 
remember. 
Breeding Populations 
Migrant flocks of canvasbacks enroute to nesting grounds 
are usually characterized by high ratios of males to fe- 
males — often as high as 2:1 (Bellrose et al. 1961). This ratio 
decreased soon after the birds arrived. Transect counts that 
measured chronological changes in breeding pair popula- 
tions showed that the best time to determine breeding densi- 
ties was at the peak of the nesting season. Olson (1964) re- 
ported that most of the drakes left the breeding area soon 
after nesting began and prevented an accurate estimate of 
the breeding numbers. The present study supported these 
conclusions. Breeding pair estimates seem most reliable 
when the drake to pair ratio reaches 1:1. At least half the 
hens at that time are on nests or have initiated nesting, and 
drakes have not yet left the area. This ratio was reached 
between 5 and 25 May in most years, and most frequently 
before 15 May. Breeding populations counted along road- 
side transects are shown in Table 8. Transect data in 1961 
were not directly comparable but indicated a breeding 
population of at least 2.3 pairs/km?. 
Two sections that were intensively searched for canvas- 
back pairs and nests in this study encompassed the former 
Roseneath study area reported by Dzubin (1952:73, 
1955:68). Breeding pair densities from 1949 to 1955 on the 
Roseneath area were compared with those found in the 
present study between 1963 and 1967. Average canvasback 
densities (breeding pairs/km?) were 3.13 + 0.85 in 1949-55 
and 3.84 + 0.73 in 1963-67. These densities were not 
significantly different (t-test; P > 0.05). Pair counts were 
not made on this area after 1967 because drainage was so 
intensive that the habitat was severely altered and water- 
fowl populations were no longer representative of the gen- 
eral study area. 
Table 7. Number and area of May wetlands by percent cover of emergent vegetation in the Minnedosa study area, 
1962-72. 


Percent coverage 

Wetlands per 



0-10 11-33 34-66 67-100 km? per year 
Species No. Ha No. Ha No. Ha No. Ha No. Ha 
Open 4,378 1,568.2 ~ — - — - _ 7.7 7.0 
Whitetop 1,479 421.2 1,083 263.3 702 134.1 623 101.7 7.0 3.9 
Cattail 956 539.5 715 358.0 482 140.9 124 26.3 oF 4.6 
Mixed 1,284 1,141.7 722 428.9 509 147.4 251 59.5 5.0 ae£ 
Bulrush 832 998.3 321 270.1 31 17.4 3 ~ 1.9 3.4 
Willows 200 30.0 130 19.9 69 8.1 6 _ 0.8 0.4 
Total 9,129 4,698.8 2,971 1,340.2 1,793 447.9 1,007 187.5 
Mean 830 427.3 270 122.3 163 40.9 92 17.0 26.3 29.0 
Percent 61 70 20 20 12 7 7 3 


