Mar 22, 1990 - Knowledge of foods consumed by ducks relative to stage of reproduction ... 'Present address: Oregon Department of Fish and Wildlife, Forest ...
Prairie Nat. 22(3):171-176.
1990.
Diet of Canvasbacks During Breeding JANE E. AUSTIN, JEROME R. SERlE I , and JAMES H. NOYES' U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center Jamestown, ND 58401 ABSTRACT - We examined diets of canvasbacks (Aythya valisinena) breeding in southwestern Manitoba during 1977 -81. Percent volume of animal foods consumed did not differ between males and females nor among prenesting, rapid follicle growth, laying, incubation, and renesting periods in females (x = 50.1 %). Tubers and shoots of fennelleaf pondweed (Potamogeton pectinatus) and midge larvae (Chironomidae) were the predominant foods, comprising on average 45% and 23% of the diet volume, respectively. Continued importance of plant foods to canvasbacks throughout reproduction contrasts with the mostly invertebrate diets of other prairie-breeding ducks, and does nor fit current theories of nutritional ecology of breeding anatids (i.e., females meet the protein requirements of reproduction by consuming a high proportion of animal foods).
Knowledge of foods consumed by ducks relative to stage of reproduction has aided our understanding of their nutrient requirements and habitat preferences during breeding (Krapu and Reinecke, in press). High energy foods are valuable to prelaying females (Krapu 1974, Hohman 1985, Noyes and Jarvis 1985) to increase fat reserves used during egg production and incubation (Drobney and Frederickson 1979, Barzen and Serie 1990). During egg-laying, females rely on foods high in protein, such as aquatic invertebrates, to supply the protein necessary for egg production (Krapu and Reinecke, in press). Bartonek and Hickey (1969) reported that the proportion of animal foods consumed by canvasbacks was greatest during breeding, but they did not differentiate results by stage of reproduction. On Ruby Lake, Nevada, the proportion of animal foods in female canvasbacks differed among reproductive periods (Noyes and Jarvis 1985). However, their intermountain study area is at the periphery of the canvasback's breeding range and may not be representative of breeding habitat for the species (Bellrose 1980). The majority of canvasbacks breed in the parklands and mixed-grass prairie of Canada and the Dakotas, with highest breeding densities in the aspen parklands of southwestern Manitoba near Minnedosa (Bellrose 1980, Stoudt 1982). We describe the diet of breeding canvasbacks in southwestern Manitoba relative to their stage of reproduction.
We determined diets of breeding canvasbacks near Minnedosa, Manitoba, adjacent to the area described by Stoudt (1982). The area lies in the aspen parkland region and is characterized by undulating topography with diverse wetland complexes (Kiel et al. 1972). Typical vegetation of these wetlands in'Present address: U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, Laurel, MD 20708 'Present address: Oregon Department of Fish and Wildlife, Forest and Range Science Laboratory, La Grande, OR 97850
cluded common cattail (Typha lattfolia) and bulrush (Scirpus spp.) in the deep
marsh zone and fennelleaf pondweed and common hornwort (Ceratophyllum dermersum)
in open water areas (Stewart and Kantrud
1971).
Foraging canvasbacks were collected on semi-permanent and permanent wetlands from late April to early July, 1977-81. Most birds were observed foraging for at least 10 minutes before collection. Esophageal contents were removed immediately and preserved in 75 % alcohol (Swanson and Bartonek 1970). The volume of each food was determined by water displacement and results were expressed as percent occurrence and mean percent volume (Swanson et al. 1974). Fragments of snail shells were excluded from calculations. Diets of females ~ere evaluated relative to their stage of reproduction. Reproductive periods were categorized by the female's ovarian condition (Hohman 1985, Barzen and Serie 1990): (1) pre nesting - from arrival until the beginning of rapid follicle growth (largest follicle diameter less than 7.5 mm); (2) rapid follicle growth (RFG) - during ovarian follicle growth, largest follicle at least 7.5 mm and no postovulatory follicles present; (2) laying - postovulatory follicles present and at least one developing follicle in the ovary or oviduct; (3) incubation - brood patch present and follicles regressed; and (4) renesting brood patch and postovulatory enlarged follicles evident and follicles developing (largest follicle at least 7.5 mm). Diets of breeding males were pooled across the breeding season. Because the number of birds collected from each reproductive period was limited, we pooled data from all years. We used multiple analysis of variance to compare mean percent volumes of plant and animal foods of male and female canvasbacks and, for females, among reproductive periods. Percentages were transformed (arcsine squareroot) before analysis to improve normality and equality of variances.
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 Percent Males --
Food
•...... -.J
"'"
PLANT Vegetation Potamogeton pectinatus Chara other Seeds ANIMAL Insecta Odonata Anisoptera Zygoptera Trichoptera Chironomidae Corixidae Dytiscidae Gastropoda Hirudinea Other
in southwestern
occurrence
Pre"
RFG
Lay
(11 )
(8)
(17)
93 93
91 64
88 75
57 7 21 43 64 64 21 0 21 14 57 14 14 21 0 7
36 9 36 55 82 64 18 9 18 18 64 9 9 18 9 27
75 0 0 38 63 63 25 0 25 25 63 12 38 12 0 0
1977-81.
Mean percent volume
Females
(14)b
'Reproductive categories: Pre = prenesting. bsample size 'tr=trace «0.1%)
Manitoba,
Males --
Females
Incub (5)
Renest
Pre
RFG
Lay
(7)
(14)
(11 )
(8)
(17)
88 65
60 60
86 86
57.8 51.0
52.3 45.6
64.0 63.9
59 6 6 65 100 100 35 6 35 53 82 24 12 47 12 0
40 0 20 20 80 80 80 40 80 80 20 0 0 80 20 0
57 14 29 57 86 86 29 14 29 14 71 14 14 14 0 29
49.8
33.6
tr
