Large bodies of shallow fresh or brackish water are preferred on migration, es- 

 pecially those with areas of aquatic plant growth (Palmer 1976b). Bellrose 

 (1976) indicated that they regularly forage in water 2-10 ft (0.6-3.0 m) deep. 



Winter and Offshore Ruddy Ducks winter in ice-free inland waters and in 

 shallow brackish or salt water areas along the coast (Palmer 1976b). Ruddy 

 Ducks wintering in the Chesapeake Bay region are found nearly exclusively on 

 slightly brackish to brackish estuarine bays and apparently only exceptionally 

 on salty estuarine bays; they avoid coastal bays and open ocean (Stewart 1962 

 Ln Johnsgard 1975). Johnsgard (1975) thought that "ideal ruddy duck wintering 

 habitat consist[ed] of brackish to slightly brackish estuaries or coastal 

 lagoons of shallow depths." 



FOOD AND FEEDING BEHAVIOR 



Siegfried (1973c) reported that adult Ruddy Ducks on the breeding grounds 

 in southern Manitoba feed almost exclusively by diving; food is strained from 

 the mud of the pond bottoms. Surface feeding by skimming and straining was 

 also seen, but Siegfried recorded this only 5 times in 810 observations of for- 

 aging adults. Young birds also feed mainly by diving but tend to make shal- 

 lower, shorter dives than do adults. Ruddy Ducks tend to dive obliquely rather 

 than vertically and, like Lesser Scaup, move longer distances from the point of 

 submergence than do Canvasbacks and Redheads. Diving intervals in water 1 ra 

 deep averaged 18.6 sec in males, 20.6 sec in females (Siegfried 1973c); the 

 longest diving time recorded for captive birds was 29 sec (Johnsgard 1975). 

 Twenty-five dives by wintering Ruddy Ducks at Brigantine NWR, New Jersey, aver- 

 aged 19.78 sec and ranged from 17.4 to 21.8 sec (Heintzelman and Newberry 1964). 

 Ruddy Ducks only rarely peck at items on the surface of the water (Siegfried 

 1973c). 



Ruddy Ducks are largely vegetarians but their diet varies with age, season, 

 and location (Bellrose 1976). Adults and young birds in Manitoba feed primarily 

 (90%) on animal foods in the summer, according to Siegfried (1973c). Larval and 

 pupal midges ( Chironomus ) are the main food items, but other insects, crusta- 

 ceans, and molluscs are also taken. In other parts of the year, plant foods ap- 

 parently make up the major portion of the diet. Widgeon grass and pondweeds 

 are the most important food items in winter in Humboldt Bay, California (Yocura 

 and Keller 1961 jji Bellrose 1976). Clams and snails are eaten most commonly in 

 the clear brackish bays of the Chesapeake region (Stewart 1962 in Bellrose 1976), 

 Cottam (1939) showed that the overall proportions of food in the diet of Ruddy 

 Ducks was about 72% plant matter and 28% animal matter. 



We know of but one study giving details on food habits of Ruddy Ducks in 

 southeastern waters. Quay and Critcher (1965) reported that the food of 75 Rud- 

 dy Ducks wintering in Currituck Sound consisted primarily of the seeds of pond- 

 weeds ( Potamogeton spp. - 23.5% by volume) and widgeongrass ( Ruppia maritima - 

 33.8%). The vegetative parts of Potamogeton (6.4%) and muskgrasses (Characaeae - 

 4.4%) also were eaten in significant amounts; another 6.0% of the diet consisted 

 of animals, primarily insects (1.4%), amphipods (2.2%), and fish eggs (1.7%). 



Further details on specific foods eaten at other times of year and in other 



459 



