Foods and dietary strategies of prairie-nesting ruddy ducks and redheads

Actively feeding Ruddy Ducks (Oxyura jamaicensis) and Redheads (Aythya americana) were collected from North Dakota wetlands during the 1979-1981 breeding seasons. Foods found within esophagi were analyzed on a wet-weight aggregate percent basis. Male and prelaying and laying female Ruddy Ducks consumed >90% invertebrates, primarily chironomids. Postlaying female Ruddy Ducks consumed 73% invertebrates. Male and female (prelaying, laying, and postlaying) Redheads were consistently more omnivorous, consuming 51-70% invertebrates (mostly chironomids) and 30-49% plant matter. Seeds of shallow marsh emergent plants were important in the diet of prelaying and laying female Redheads in 1979, a wet year. Female Redheads used temporally available seed resources in shallow marshes to meet energy requirements for foraging on invertebrates in deeper, more permanent wetlands. Continued losses of easily drained shallow wetlands may represent a serious impediment to our efforts to maintain current Redhead population levels.