“Its intimate habits, its stupidity, its curious nesting customs and ludicrous courtship performance place it in a niche by itself. Even its eggs are unique in appearance and are deposited in a slip-shod, irregular manner that is most extraordinary. Everything about this bird is interesting to the naturalist, but almost nothing about it is interesting to the sportsman." J. C. Phillips, A Natural History of Ducks, Phillips 1926a
This small-bodied, stiff-tailed duck is still disdained by most hunters and ranks as a pest species in Europe, where it has been introduced. Birders appreciate it, however, because adult males are richly colored with a striking, bright, sky-blue bill and have a highly entertaining courtship display. Indeed, compared with other North American ducks, the Ruddy Duck is unusual in almost every aspect of its biology.
Unlike most waterfowl, pairs form on the breeding grounds. Males perform unique, comical courtship displays and establish seasonally monogamous pair bonds, but some males are polygynous. Females lay large, rough, white eggs in well-concealed nests over water; their eggs are the largest relative to body size of all waterfowl, with a correspondingly high energetic cost of egg production. Highly precocial ducklings are tended by the female only and for a shorter period of time than most ducks. Some non-paternal males are known to accompany the brood but provide no care. Unusual among waterfowl, except other stiff-tailed ducks, a small percentage of Ruddy Ducks apparently undergo 2 remigial molts per year.
Ruddy Duck populations are stable or increasing throughout most of the North American breeding range. This species breeds primarily in the prairie pothole region of North America and is a common winter resident of brackish to saline coastal habitats and large inland water bodies. Adults and ducklings are mostly carnivorous and feed extensively on midge larvae (Diptera: Chironomidae), almost to the point of being a specialist on these insects.
Most research on this species has concentrated on 1 or more of its unusual aspects. Substantive information is available from southwest Manitoba on bioenergetics of egg formation (Alisauskas and Ankney Alisauskas and Ankney 1994a , Alisauskas and Ankney 1994b ) and nesting ecology ( Brua 1999 ). Studies of foraging behavior in captives are excellent (Tome Tome 1988 , Tome 1989b ; Tome and Wrubleski 1988 ). Studies of nest parasitism in Utah also provide valuable information (Joyner Joyner 1976 , Joyner 1983 ). Due to their unique habits and interest to birders, stiff-tails have been covered in an excellent compilation by Johnsgard and Carbonell ( Johnsgard and Carbonell 1996 ). Future studies on adult survival, mating-system genetics, dispersal, and wintering ecology would be helpful.