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.
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