Habitat Use and Productivity of Canvasbacks 
in Southwestern Manitoba, 1961-72 
by 
Jerome H. Stoudt 
U.S, Fish and Wildlife Service 
Northern Prairie Wildlife Research Center 
P.O. Box 1747 
Jamestown, North Dakota 58401 
Abstract 
A study of canvasbacks (Aythya valisineria) breeding populations, nest success, productivity, and habitat 
requirements was conducted from 1961 to 1972 on a 181.3-kim? area south of Minnedosa, Manitoba. 
Additional survey work was conducted in an area northwest of Minnedosa, These areas lie in the aspen 
parklands and are characterized by a diverse wetland complex. Land use in the region is primarily small 
grain farming, which has rapidly converted much of the woodland and grassland area to agriculture. 
Wetlands in early spring varied from 18 to 43/km? (average 26/km?) with a mean area of 0.5 ha, Most 
wetlands were 0.2 ha or less and ranged from 0.3 to 0.9 m deep. Seventy-one percent of the wetlands 
were located in cultivated land and a majority had open shorelines. Breeding pair populations ranged 
from 2.3 to 4.1/km2 and were highest on Type 5 wetlands over 0.4 ha with less than one-third of the 
water surface covered with emergent vegetation. Nesting usually began the first week in May and success 
for 1.858 active nests from 1962 to 1972 ranged from 32 to 62% (average 45%). Hen success adjusted 
for renesting was 56% . Nesting canvasback hens most frequently used semipermanent (Type 4) wetlands 
less than 0.4 ha in area containing cattail (Typha latifolia) or hardstem bulrush (Scirpus acuttus), No 
differences were found in nest success between wetland types, Of all canvasback nests examined, 57% 
were parasitized by redheads (Aythya americana). The average number of redhead eggs per parasitized 
nest was 3.2. Canvasback clutch size was reduced by about 1.0 egg in nests that were parasitized. More 
canvasback renests were parasitized by redheads than first nests. Predation accounted for 86% of the 
nest losses. and flooding, desertion, and burning made up the remainder. Raccoons (Procyon lotor) 
destroved 64% of the nests lost to predators and accounted for 56% of all nest failures. Disturbance 
by field workers locating nests and flushing hens did not affect nest success. Mean brood size was 5.9. 
5.6. and 5.3, for Class I, IL. and II broods, respectively, and 5.8 for all broods, Juvenile mortality 
averaged 21% from hatching to Class I. Canvasback production totaled 1.5 broods/km?* and averaged 
7.7 young fledglings/km2. Productivity (broods per pair) declined for the period 1949-55 to 1962-67 
but numbers of broods/km? were not significantly different. Brood use was highest on semipermanent 
and permanent (Type 4 and 5) wetlands larger than 0.8 ha with less than one-third of the surface covered 
by emergent vegetation. Canvasbacks used a diversity of Type 3, 4. and 5 wetlands during the active 
breeding period for feeding, nesting, and brood rearing. Evidence suggests that canvasbacks require 
a secure nesting site in a diversified wetland complex containing a variety of size. permanency. and 
cover types. 
An extensive drought in the prairie pothole region of the 
United States and Canada began to affect breeding habi- 
tat of canvasbacks (Aythya valisineria) as early as 1957 
(Stoudt 1971), Continental breeding populations of this 
species began to decline and restrictive regulations were 
initiated in 1958 to lessen the effect of hunting on breeding 
populations (Reeves and Carney 1976). During the 1960-63 
hunting seasons, a complete closure was imposed on canvas- 
backs in the United States to further protect remaining 
numbers. In view of the population status of canvasbacks 
and the new wetland habitat preservation programs begun 
during the post-drought period in the United States and 
Canada, it became imperative to learn as much as possi- 
ble about breeding habitat requirements of this species. 
Consequently the U.S. Fish and Wildlife Service (FWS) 
initiated research on the breeding habitat requirements of 
‘anvasbacks in 1961, The principal purpose of this study 
was to gather basic information for establishing manage- 
ment programs to preserve and improve habitat for can- 
vasbacks and other species of overwater nesting waterfowl. 
One of the first major publications dealing with canvas- 
back breeding biology was Hochbaum’s (1944) classic. “The 
Canvasback on a Prairie Marsh,” Most of this book dealt 
with canvasbacks on Delta Marsh, a habitat type particu- 
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