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Diet of Canvasbacks During Breeding

Results

Canvasbacks consumed both plant and animal material throughout the breeding season (Table 1). The proportion of plant and animal foods consumed did not differ among reproductive periods in females (F = 0.58; 4 df, P = 0.678), nor between males and females (F = 0.64, 1 df, P = 0.427). The lack of significant differences is probably due in part to the great variability of diets among individuals. Fennelleaf pondweed and midge larvae were the predominant foods except during incubation in females, when snails were the major animal food. Overall, remnants of Gyraulus, Lymnaea, and Helisoma snails occurred in 23 females and 6 males.

Plant foods consisted primarily of tubers and shoots of fennelleaf pondweed. Tubers contributed 91% of the total pondweed volume when tubers and shoots were measured separately. Seeds occurred in about half of the samples, but the volume was relatively small (Table 1). Seeds from pondweed and Amaranthus comprised more than 60% of total seed volume.

Table 1.  Foods consumed by breeding canvasbacks in southwestern Manitoba, 1977-81.
Food Percent occurrence Mean percent volume
Males Females Males Females
(14)b Prea
(11)		 RFG
(8)		 Lay
(17)		 Incub
(5)		 Renest
(7)		 (14) Pre
(11)		 RFG
(8)		 Lay
(17)		 Incub
(5)		 Renest
(7)
PLANT 93 91 88 88 60 86 57.8 52.3 64.0 42.8 32.2 51.0
  Vegetation 93 64 75 65 60 86 51.0 45.6 63.9 41.1 32.1 50.9
     Potamogeton pectinatus 57 36 75 59 40 57 49.8 33.6 63.9 40.4 32.1 50.9
     Chara 7 9 0 6 0 14 trc tr 0 0.5 0 tr
     other 21 36 0 6 20 29 1.2 12.0 0 0.2 0 tr
  Seeds 43 55 38 65 20 57 6.8 6.8 0.2 1.8 0.1 0.1
ANIMAL 64 82 63 100 80 86 42.2 47.7 36.6 57.1 67.7 49.0
  Insecta 64 64 63 100 80 86 40.7 46.3 35.9 48.4 11.0 41.4
     Odonata 21 18 25 35 80 29 2.1 9.1 0.3 2.5 1.1 5.3
         Anisoptera 0 9 0 6 40 14 0 0 0 1.4 0.2 5.3
         Zygoptera 21 18 25 35 80 29 2.1 9.1 0.3 1.1 1.1 0.9
     Trichoptera 14 18 25 53 80 14 1.4 0.2 11.9 9.9 4.2 0.7
     Chironomidae 57 64 63 82 20 71 36.6 37.0 23.6 35.8 5.5 34.3
     Corixidae 14 9 12 24 0 14 tr tr tr 0.2 0 tr
     Dytiscidae 14 9 38 12 0 14 6.7 tr 0.1 tr 0 0.2
  Gastropoda 21 18 12 47 80 14 1.5 0.1 tr 8.4 56.4 7.6
  Hirudinea 0 9 0 12 20 0 0 1.2 0 0.4 0.4 0
  Other 7 27 0 0 0 29 tr tr 0 0 0 tr
a Reproductive categories: Pre = prenesting, RFG = rapid follicle growth, Lay = Laying; Incub = incubation; and Renest = renesting.
b sample size
c tr = trace (<0.1%)
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