Canvasback--BIOLOGICAL AND ECOTOXICOLOGICAL CHARACTERISTICS OF TERRESTRIAL VERTEBRATE SPECIES RESIDING IN ESTUARIES

Canvasback Contaminant Exposure Data
I.	Organochlorine Contaminants
1.	Between 1963 and 1965, fat was analyzed from Canvasbacks (N=4) which were collected from areas in California where pesticides were thought to be present (Keith and Hunt 1966). The following concentrations (ug/g ww) were the mean of the four analyses: DDT (2.88), DDE (54.41), DDD (2.10), Dieldrin (0.00), Endrin (0.00).
2.	In 1972 and 1973, Canvasback eggs were collected and analyzed from Nevada, Alberta, Saskatchewan, Manitoba and North Dakota (Stendell et al. 1977). The mean concentrations (ug/g ww) in Nevada (N=11) were DDE (0.74), DDT (0.03), Dieldrin (n.d.), HCB (0.02) and PCBs (0.89), Alberta (N=5) DDE (0.29), DDT (n.d.), Dieldrin (n.d.), HCB (n.d.) and PCBs (0.33), Saskatchewan (N=24) DDE (0.18), DDT (0.01), Dieldrin (0.01), HCB (n.d.) and PCBs (0.93), Manitoba (N=51) DDE (0.39), DDT (0.03), Dieldrin (0.01), HCB (0.01) and PCBs (1.1), North Dakota (N=6) DDE (0.20), DDT (n.d.), Dieldrin (n.d.), HCB (n.d.) and PCBs (0.51).
3.	Canvasback carcasses were collected and analyzed for organochlorine residues from Chesapeake Bay, Maryland in 1973 and 1975 (White et al. 1979). The mean concentrations (ug/g ww) in 1973 (N=29) were DDE (0.36), DDT (n.d.), DDD (n.d.), Dieldrin (0.19), PCBs (1.5), Toxaphene (n.d), cis-chlordane (n.d.), trans-nonachlor (n.d.), Oxychlordane (n.d.), Hexachlorobenzene (n.d.) and Heptachlor epoxide (n.d.). In 1975 (N=113) DDE (0.56), DDT (0.18), DDD (0.11), Dieldrin (0.19), PCBs (2.7), Toxaphene (0.17), cis-chlordane (0.19), trans-nonachlor (0.14), Oxychlordane (0.12), Hexachlorobenzene (0.15) and Heptachlor epoxide (0.11).
4.	Five male and one female Canvasbacks from Ontario County, New York had liver, muscle, and brain tissues analyzed for PCBs (Baker et al 1976). Three of the males and the one female had either no detections or levels below detection limits for PCBs. The concentrations (ug/g ww) of male one were, liver: PCBs (16.1), muscle: PCBs (2.8), brain: PCBs (10.2). In male two, liver: PCBs (1.4), muscle: PCBs (0.6), brain: PCBs (1.0).
5.	In 1980 and 1981, Canvasback wings from California ( SanFrancisco Bay and the Salton Sea) were collected from hunters and analyzed for organochlorine residues (Ohlendorf and Miller 1984). The mean concentrations (ug/g ww) of four male wings from San Francisco Bay were DDE (0.46), Dieldrin (0.02) and PCBs (1.6), four female wings, DDE (0.05) and PCBs (0.30). Five combined male and female wings from the Sultan Sea had concentrations of DDE (1.2) and PCBs (0.34).
6.	42 Canvasbacks were collected from San Francisco Bay, California in 1988 (Miles and Ohlendorf 1993). Carcasses were analyzed for organochlorines with the mean concentrations (ug/g ww, N=42) being PCBs (1.079), trans-nonachlor (0.013), heptachlor epoxide (0.012), Oxychlordane (0.011), Dieldrin (0.017), DDT (0.011), DDD (0.012), DDE (0.386). Skin and fat were pooled and analyzed for PAHs with the mean concentrations (ug/g ww, N=42) being 1,2-Benzanthracene (n.d.), Chrysene (n.d.), Fluoranthrene (n.d.), Fluorene (0.010), Napthalene (0.018), Phenanthrene (0.022), Pyrene (n.d.), n-Dodecane (0.116), n-Tridecane (0.067), n-Tetradecane (0.098), n-Pentadecane (0.092), n-Hexadecane (0.056), n-Heptadecane (0.154), n-Octadecane (0.065), n-Nonadecane (0.046), n-Eicosane (n.d.), Phytane (0.074), Pristane (0.056), Octylcyclohexane (n.d.) and Nonylcyclohexane (n.d.).
7.	Canvasback carcasses were collected at Fighting Island, Michigan between Autumn 1993 and Winter 1994 (Mazak et al. 1997). Mean organochlorine concentrations (ug/g lw, N=6) were HCB (0.023), PCB 28 (0.003), and PCB 149 (0.017).
II.	Cholinesterase-Inhibiting Pesticides
	No direct exposure data available
III.	Trace Elements, Metals, and Metalloids
1.	Between 1938 and 1953, Canvasbacks were collected from across North America, and their gizzards were analyzed for ingested Pb shot (Bellrose 1959). Canvasback gizzards (N=1216) from across North America were analyzed for the numbers of Pb shot pellets contained in each gizzard and the findings were 8.8% of gizzards contained 1 pellet, 1.07% contained 2 pellets, 0.99% contained 3 pellets, 3.29% contained 4 pellets, 0.08% contained 5 pellets, 0.25% contained 6 pellets and overall, 11.84% of all gizzards contained pellets. Between 1938 and 1954, Canvasbacks were collected from the Atlantic, Mississippi, Central and Pacific flyways of North America and their gizzards were analyzed for ingested Pb shot. From the Atlantic flyway, 128 gizzards were analyzed and 11.7% contained Pb shot. 413 gizzards were analyzed from the Mississippi flyway and 6.8% contained Pb shot. 222 gizzards were analyzed from the Central flyway and 5.4% contained Pb shot. 871 gizzards were analyzed from the Pacific flyway and 12.7% contained Pb shot. During the 1949, 50, and 51 hunting seasons, Canvasbacks were collected from Hovey Lake, Indiana and analyzed for ingested Pb shot. 4 gizzards were analyzed in 1949 with 0 containing Pb shot, 6 gizzards were analyzed in 1950 with 0 containing Pb shot and 5 gizzards were analyzed in 1951 with 0 containing Pb shot. Between 1938 and 1953, 88 Canvasback gizzards were analyzed from the Illinois River, IL with 11.36% containing Pb shot and 136 gizzards were analyzed from the Mississippi River, IL with 5.15% containing Pb shot. Between 1938 and 1954, 144 Canvasbacks gizzards were analyzed from North America all of which contained Pb shot. Of these gizzards, 74.3% contained one pellet, 9.0% contained two pellets, 8.3% contained three pellets, 2.8% contained four pellets, 0.7% contained five pellets, 2.1% contained six pellets and 2.8%contained over six pellets.
2.	Canvasbacks were collected from the eastern United States and livers were analyzed for Pb concentrations (Bagley and Locke 1967). Mean liver concentrations (ug/g ww) (N=4) of Pb were 0.5.
3.	Between 1972 and 1973 Canvasback eggs were collected from different locations and analyzed for Hg residues (Stendell et al. 1977). The mean concentrations (ug/g ww) were: Nevada (N=5, 0.08), Alberta (N=4, all < 0.05), Saskatchewan (N=6, 0.04), Manitoba (N=14, 0.04) and North Dakota (N=5, all<0.05).
4.	Canvasback carcasses were collected and tissues were analyzed for heavy metal residues from Chesapeake Bay, Maryland in 1973, 1975, and 1976 (White et al. 1979). Mean liver concentrations (ug/g ww) in 1973 were Pb (N=29, 0.25), Cd(N=29, 0.59), Cu(N=29, 59), Zn(N=29, 41), Hg(N=10, 0.24), Cr(N=10,0.02). Mean liver concentrations (ug/g ww, N=87) of Pb in 1975 were 0.14 and in 1976 (N=70) were 0.19. Mean kidney concentrations (ug/g ww) of Cd in 1975 (N=113) were 2.3 and in 1976 (N=69) were 2.3. Mean concentrations (ug/g dw, N=78) of Pb in wing bones in 1975 were 7.8. Lead residues between 1973 and 1975, 1976 differ significantly.
	Canvasbacks were collected during December 1970 and March 1971 from Chesapeake Bay, Maryland and West River, Maryland and breast tissue was analyzed for Hg (Baskett 1975). Eight Canvasbacks were collected from Chesapeake Bay, Maryland in December 1970 and had Hg concentrations (ug/g ww) in breast tissue of 0.09, 0.16, 0.05, 0.22, 0.11, 0.24, 0.15 and 0.10. Eight Canvasbacks were collected from West River, Maryland in December 1970 and had Hg concentrations (ug/g ww) in breast tissue of 0.16, 0.08, 0.08, 0.08, 0.12, 0.08, 0.10 and 0.08.
	Five male, and one female Canvasbacks from Ontario County, New York had liver, muscle, and brain tissues analyzed for heavy metals (Baker et al 1976). Three of the males had either no detections or levels below detection limits for trace metals. The concentrations (ug/g ww) of male one were, liver: Pb (12.6), muscle: Hg (0.048), brain: Pb (12.6). In male two, muscle: Hg (0.039). In one female, concentrations of Hg in the brain were 0.047 and the liver was 0.047.
	In 1976 and 1977 Canvasbacks were collected from LaCrosse, WI and Keokuk, IA and livers, wing bones and kidneys were analyzed for metals (Fleming 1981). Livers were analyzed for Hg in LaCrosse and the concentrations (ug/g ww) in 1976 were: adult males (N=5, 0.11), adult females (N=5, 0.07), immature males (N=5, 0.08) and immature females (N=5, 0.12), and in 1977 the concentrations were: adult males (N=5, 0.04), adult females (N=5, 0.08), immature males (N=4, 0.03) and immature females (N=1, 0.04). Livers were analyzed for Hg in Keokuk and the concentrations (ug/g ww) in 1976 were: adult males (N=5, 0.09), adult females (N=5, 0.07), immature males (N=5, 0.12) and immature females (N=5, 0.08), and in 1977 the concentrations were: adult males (N=5, 0.10), adult females (N=5, 0.07), immature males (N=1, 0.04) and immature females (N=1, 0.04). Wing bones were analyzed for Pb in LaCrosse and the concentrations (ug/g ww) in 1976 were: adult males (N=5, 18), adult females (N=5, 5.4), immature males (N=5, 0.76) and immature females (N=5, 0.98), and in 1977 the concentrations were: adult males (N=5, 11), adult females (N=5, 7.6), immature males (N=5, 0.68) and immature females (N=1, <0.5). Wing bones were analyzed for Pb in Keokuk and the concentrations (ug/g ww) in 1976 were: adult males (N=5, 6.3), adult females (N=5, 4.6), immature males (N=5, 0.53) and immature females (N=5, 1.3), and in 1977 the concentrations were: adult males (N=5, 1.7), adult females (N=5, 3.9), immature males (N=1, 18) and immature females (N=1, <0.5). Kidneys were analyzed for Cd in Keokuk and the concentrations (ug/g ww) in 1976 were: adult males (N=5, 1.1), adult females (N=5, 1.6), immature males (N=5, 0.12) and immature females (N=5, 0.05). Livers were analyzed for Ni in Keokuk and the concentrations (ug/g ww) in 1976 were: adult males (N=5, 0.02), adult females (N=5, 0.02), immature males (N=5, 0.02) and immature females (N=5, <0.02).
	45 Canvasbacks were collected between the states of Minnesota, Michigan, Missouri, Ohio, Illinois and Kentucky during the 1977-1979 hunting seasons (Anderson et al. 1987). Of the 45 Canvasbacks collected, 4 (8.9%) had ingested shot in their gizzards. Of this shot, 100% was Pb. During the 1938-1954 hunting seasons, Canvasbacks were collected from 7 states of the Mississippi flyway (N=413) with 6.8% having ingested shot (includes both Pb and steel), and during the 1977-1979 hunting seasons, Canvasbacks were collected from 11 states of the Mississippi flyway (N=45) with 6.7% having ingested shot (includes both Pb and steel).
	Between the wintering seasons of 1976-1977 and 1979-1980 Canvasbacks from Chesapeake Bay were collected, and the liver, kidneys and ulnar bones were analyzed for metals (Di Giulio and Scanlon 1984). The mean concentrations (ug/g dw) in livers (N=64) for Cd was 3.10 and for Pb was 3.8. The mean concentrations (ug/g dw) in kidneys (N=63) for Cd was 6.00 and for Pb was 13.3 The mean concentrations (ug/g dw) in ulnar bones (N=65) for Zn was 157 and for Pb was 7.0. The mean concentrations (ug/g dw) in livers (N=64) for Zn was 170 and for Cu was 113.7. The mean concentrations (ug/g dw) in kidneys (N=63) for Zn was 103 and for Cu was 26.6.
	Between November 1987 and February 1988 Canvasbacks were collected from Catahoula Lake Louisiana and the Mississippi River delta for analysis of the presence of lead pellets in gizzards (Hohman et al. 1990). Immature males and females analyzed from Catahoula Lake; November (N=29, 17% contained ingested Pb shot), December (N=31, 65% contained ingested Pb shot), January (N=22, 23% contained ingested Pb shot) and February (N=26, 35% contained Pb shot). Adult males and females analyzed from Catahoula Lake; November (N=17, 6% contained ingested Pb shot), December (N=22, 45% contained ingested Pb shot), January (N=29, 7% contained ingested Pb shot) and February (N=28, 21% contained Pb shot). Canvasbacks were also collected from the Mississippi River delta. Immature males and females collected (N=82) between November and February had 8% containing Pb shot. Adult males and females collected (N=118) between November and February had 1% containing Pb shot.
	Between November 1987 and February 1988, Canvasbacks were collected from Catahoula Lake Louisiana and the Mississippi River delta for analysis of trace elements and metals (Custer and Hohman, 1994). Livers of males (N=40) and females (N=80) were analyzed for concentrations (ug/g dw) of Pb, and mean concentrations of Pb from Catahoula Lake were: Females (November (0.19), December (10.9), January (2.7), February (1.7)) and males: (December (47.2), February (5.5)). Mean concentrations of Pb from the Mississippi River delta were females: (November (0.32), December (0.17), January (0.15) and February (0.32)) and males: (December (0.23) and February (1.1)). Livers of females (N=80) were also analyzed for concentrations (ug/g dw) of Fe. Mean concentrations of Fe from Catahoula Lake were (November (3003), December (3649), January (3764) and February (3877)) and from the Mississippi River delta (November (2501), December (4504), January (6337), February (7048)). Female (N=20) Canvasbacks were collected in December and January and livers were analyzed for Se and Hg concentrations. Mean concentrations (ug/g dw) of Se from Catahoula Lake were 4.0 and from the Mississippi River Delta were 3.6. Mean concentrations of Hg from Catahoula Lake were 0.32 and from the Mississippi River delta were 0.18. Female Canvasbacks were collected from Catahoula Lake and the Mississippi River delta and livers were analyzed for concentrations of Cd, Cu, Mg, Mn, and Zn. Mean concentrations (ug/g dw) from Catahoula Lake (N=40) were Cd (0.43), Cu (187), Mg (604), Mn (11.7), and Zn (137). Mean concentrations (ug/g dw) from the Mississippi River Delta (N=40) were Cd (0.66), Cu (85), Mg (604), Mn (12.4) and Zn (128).
	42 Canvasbacks were collected from San Francisco Bay, California in 1988 (Miles and Ohlendorf 1993). Liver and kidneys were analyzed for trace element concentrations (ug/g dw). Mean concentrations in livers (N=42) were: Al (n.d.), As (0.25), Cd (0.56), Cr (n.d.), Cu (99.1), Fe (618), Hg (3.09), Ni (n.d.), Pb (0.43), Se (13.2), and Zn (160). Mean concentration of Cd in kidneys (N=42) was 2.30.
	Canvasbacks were collected from the Mississippi flyway during the 1996-1997 hunting season, and their gizzards were analyzed for shotgun pellets (toxic and nontoxic) (Anderson et al. 2000). Gizzards (N=63) analyzed in Minnesota for ingested shot revealed four gizzards with ingested shot. Two gizzards contained Pb shot and two contained nontoxic shot. Gizzards (N=90) analyzed in Wisconsin for ingested shot revealed seven gizzards with ingested shot. Two gizzards contained Pb shot and five contained nontoxic shot. Gizzards (N=23) analyzed from other Mississippi flyway states for ingested shot revealed six gizzards with ingested shot. One gizzard contained Pb shot and five contained nontoxic shot. Gizzards (N=176) from the Mississippi flyway were analyzed for shot-in toxic and nontoxic shot which revealed 14 gizzards with shot-in shot. All of these gizzards contained nontoxic shot.
IV.	Petroleum
	No residue data available
Canvasback Contaminant Response Data
I.	Organochlorine Contaminants
	No response data available
II.	Cholinesterase-Inhibiting Pesticides
	No response data available
III.	Trace Elements, Metals, and Metalloids
	No response data available
IV.	Petroleum
	No response data available
References for Canvasback
Anderson, W. L., Havera, S. P., Montgomery, R. A. 1987. Incidence of ingested shot in waterfowl in the Mississippi Flyway, 1977-1979. Wildlife Society Bulletin 15:181-188.
Anderson, W. L., Havera, S. P., Zercher, B. W. 2000. Ingestion of lead and nontoxic shotgun pellets by ducks in the Mississippi Flyway. Journal of Wildlife Management 64:848-857.
Bagley, G. E., Locke, L. N. 1967. The occurrence of lead in tissues of wild birds. Bulletin of Environmental Contamination and Toxicology 2:297.
Baker, F. D., Tumasonis, C. F., Stone, W. B., Bush, B. 1976. Levels of PCB and trace metals in waterfowl in New York State. New York Fish and Game Journal 23(1):82-91.
Baskett, T. S. 1975. Mercury residues in breast muscle of wild ducks, 1970-71. Pesticides Monitoring Journal 9:67-78.
Bellrose, F. C. 1959. Lead poisoning as a mortality factor in waterfowl populations. Illinois Natural History Survey Bulletin 27:235-288.
Bull, J. and J. Farrand, Jr. 1977. The Audubon Society Field Guide to North American Birds. Alfred A. Knopf, New York. 455 pp.
Custer, C. M., Custer, T. W. 1996. Food habits of diving ducks in the Great Lakes after the Zebra Mussel Invasion. Journal of Field Ornithology 67(1):86-99.
Custer, T. W., Hohman, W. L. 1994. Trace elements in canvasbacks (Aythya valisineria) wintering in Louisiana, USA, 1987-1988. Environmental Pollution 84(3):253-259.
Di Guilio, R. T., Scanlon, P. F. 1984b. Heavy metals in tissues of waterfowl from the Chesapeake Bay, USA. Environmental Pollution 35:29-48.
Dieter, M. P., Perry, M. C., Mulhern, B. M. 1976. Lead and PCB’s in canvasback ducks: relationship between enzyme levels and residues in blood. Archives of Environmental Contamination and Toxicology 5(1):1-13.
Fleming, W. J. 1981. Environmental metal residues in tissues of canvasbacks. Journal of Wildlife Management 45:508-511.
Fournier, M. A., Hines, J. E. 1998. Productivity and population increase of subarctic breeding canvasbacks. Journal of Wildlife Management 62(1):179-184.
Hohman, W. L., Pritchert, R. D., Pace, R. M. III, Woolington, D. W., Helm, R. 1990. Influence of ingested lead on body mass of wintering canvasbacks. Journal of Wildlife Management 54(2):211-215.
Hohman, W. L., Woolington, D. W., Devries, J. H. 1990. Food habits of wintering canvasbacks in Louisiana. Canadian Journal of Zoology 68(12):2605-2609.
Jarvis, R. L., Noyes, J. H. 1986. Foods of canvasbacks and redheads in Nevada: Paired male and ducklings. Journal of Wildlife Management 50(2):199-203.
Johnson, D. H., Grier, J. W. Determinants of breeding distributions of ducks. Wildlife Monographs 100:1-37.
Keith, J. O., Hunt, E. G. 1966. Levels of insecticide residues in fish and wildlife in California. Transactions of the North American Wildlife and Natural Resource Conference 31:150-177.
Madge S. and H. Burn 1988. Waterfowl. Houghton Mifflin, Boston. 245 pp.
Maxson, S. J., Riggs, M. R. 1996. Habitat use and nest success of overwater nesting ducks in Westcentral Minnesota. Journal of Wildlife Management 60(1):108-119.
Mazak, E. J., MacIsaac, H. J., Servos, M. R., Hesslein, R. 1997. Influence of feeding habits on organochlorine contaminant accumulation in waterfowl on the Great Lakes. Ecological Applications 7(4):1133-1143.
Miles, A. K., Ohlendorf, H. M. 1993. Environmental contaminants in canvasbacks wintering on San Francisco Bay, California. California Fish and Game 79(1):28-38.
Noyes, J. H., Jarvis, R. L. 1985. Diet and nutrition of breeding female redhead and canvasback ducks in Nevada. Journal of Wildlife Management 49(1):203-211.
Ohlendorf, H. M., Miller, M. R. 1984. Organochlorine contaminants in California waterfowl. Journal of Wildlife Management 48(3):867-877.
Sorenson, M. D. 1993. Parasitic egg laying in canvasbacks: Frequency, success, and individual behavior. Auk 110(1):57-69.
Stendell, R. C., Cromartie, E., Wiemeyer, S. N., Longcore, J. R. 1977. Organochlorine and Mercury Residues in Canvasback Duck Eggs, 1972-73. Journal of Wildlife Management 41(3):453-457.
Stewart, R. E., Geis, A D., Evans, C. D. 1958. Distribution of populations and hunting kill of the canvasback. Journal of Wildlife Management 22: 333-370.
Tome, M. W., Wrubleski, D. A. 1988. Underwater foraging behavior of canvasbacks, lesser scaups, and ruddy ducks. Condor 90:168-172.
White, D. H., Stendell, R. C., Mulhern B. M. 1979. Relations of wintering canvasbacks to environmental pollutants-Chesapeake Bay, Maryland. Wilson Bulletin 91(2):279-287.

Species	The length of the Canvasback (Aythya valisineria) varies from 48-61 cm long (Bull and Farrand, 1977) with males having a mean body mass of 1366 grams and females 1311 grams (Dieter et al. 1976). Adult males have a chestnut head and neck with a black breast and upper mantle. Body and wings are a very pale gray while the tail feathers are blackish in color. Females have a chestnut neck and breast with a pale gray body and wings. Tail and rump are dark brown. In flight both males and females have a pale appearance with little contrast between body and wings Madge and Burn 1988).
Status in Estuaries	Canvasbacks breed on prairie marshes with a mix of open water and fringe vegetation (Madge and Burn 1988). Almost one third of the Canvasback population breeds in the boreal areas of Northwestern North America (Fournier and Hines 1998). Nests are usually found in inland fresh water marshes of medium depth and are typically found floating, attached to various marsh plants; however, plants are not particularly dense around nests.(Maxson and Riggs 1996). Females begin to nest in late April or early May and lay seven to nine greenish colored eggs which hatch in approximately 25 days. Upon hatching Canvasback young are precocial as they begin to feed themselves soon after hatching; although, the female leads and protects her brood for up to sixty days. Most Canvasbacks arrive at breeding grounds already in pair-bonds and take up fairly large territories as they are solitary nesters (Sorenson 1993).
Abundance and Range	The summer breeding range of the Canvasback extends from northeastern California and Nebraska northward across the western prairies and great plains to central Alaska and extends eastwards to Minnesota (Madge and Burn 1988). During the winter, Canvasbacks can be found along the Atlantic, Pacific and Gulf Coasts of the United States and Mexico. To a lesser degree they can also be found in the Southern Great Lakes region, the lower Mississippi River Valley, the southern plains, western desert areas and central Mexico (Stewart et al. 1958). In the mid 1970s, the population was estimated to be 500,000 which was 50% less than 20 years earlier. Although the population fluctuates considerably, it seems to be declining (Madge and Burn 1988).
Site Fidelity	Strongly philopatric (Johnson and Grier 1988).
Ease of Census	Moderate
Feeding Habits	Canvasbacks do majority of their feeding underwater either on or below the substrate. They insert their bills perpendicular to the substrate surface and use a rapid shaking motion to dislodge plant and animal material and then return to the surface to consume it (Tome and Wrubleski 1988) Typically plant material makes up greater than 90 percent of a Canvasbacks diet. During the winter and pre-laying stage of the breeding season, both males and females feed almost exclusively on plant matter from plants such as Potamogeton, Scirpus, Sagittaria, Vallisneria and others. (Hohman et al. 1990). Males continue to feed on plant material throughout the year, but during egg laying and brooding, females and their new ducklings may switch to a diet that contains greater than 90% animal matter before switching back to a diet of mainly plant matter in the fall. Animal matter consumed includes small clams and snails as well as dragonfly nymphs and caddis fly larvae (Noyes and Jarvis 1985; Jarvis and Noyes 1986). It has also been shown that Canvasbacks may consume a small amount of the invasive zebra mussel in the Great Lakes region (Custer and Custer 1996).