
Fig. 7. Type 5 wetland (Shaw and Fredine 1956) in the Minnedosa study area. 
to support nests. During early May, nest cover was limited 
to vegetation that remained standing from the previous 
year. Wetlands with a known history of canvasback nests 
were searched each year. Nest searching on the extensive 
study area was generally confined to the areas of known 
or suspected use because the objective was to find as many 
nests as possible. 
When a hen was seen on a nest before she flushed, the 
searchers did not disturb her. Hens which were never 
flushed yielded information regarding possible bias in nest 
success caused by flushing. However, most canvasback nests 
were found by flushing the hen and then locating the nest. 
Nests deserted due to disturbance by the search crew were 
not included in calculations of nest success. 
When a nest was located, data were recorded at the site, 
the eggs were covered with down, and the observers left 
the site quickly to avoid further disturbing the hen or 
attracting predators. Data were collected on nest material, 
nest cover, clutch size, incubation stage, and egg parasitism. 
Care was taken to straighten trampled cover and leave as 
little sign as possible near the nest. A willow stick with a 
plastic or cloth marker was placed 9 m or more from the 
nest. Nest data were recorded on individual survey forms. 
Most nests were revisited after expected hatching dates to 
determine success, parasitism by redheads, and other fac- 
tors. Most nests were rechecked after violent storms. 
Brood Counts 
Brood surveys were conducted on the same areas used 
for breeding pair counts. Additional data were obtained 
from observations made in areas adjacent to the transects. 
