This diving duck, restricted to North America, breeds widely throughout the Prairie Pothole Region of the United States and Canada. It also nests in dense concentrations in marshes of the western United States. In contrast to its extensive breeding distribution, the Redhead in winter is concentrated mostly in coastal areas along the Gulf of Mexico, with hundreds of thousands of birds traditionally found in the Laguna Madre of Texas and the Laguna Madre of Tamaulipas, Mexico.
The Redhead begins arriving in its winter range in October. The species depends heavily on rhizomes of shoalgrass (Halodule wrightii), a seagrass species, for winter nutrition. Pairs begin to form on the winter range, and by the time the last birds have left on their northward migration in March, pair formation is well under way. Monogamous pair bonds continue developing rapidly in small migrating flocks, with birds initiating nesting by early May and extending at least into late June. Nests are constructed in dense emergent vegetation (usually cattail [Typha] or bulrush [Scirpus] spp.) of deep marshes.
The Redhead demonstrates facultative brood parasitism to a greater extent than any other North American duck. A breeding female chooses 1 of 3 laying strategies: (1) lays her own clutch, (2) parasitizes other nests before laying her clutch, or (3) parasitizes other duck nests without producing a clutch of her own. Inter- and intraspecific egg parasitism is very common with this species; parasitic egg-laying has been known to increase nest abandonment and depress clutch size, nest success, and egg success for some host species. Males usually abandon their mates early in incubation, after which they and unsuccessful females congregate in large flocks on Canadian lakes to undergo molt and to stage for fall migration.
This wide-ranging species exhibits a high degree of flexibility in habitat and food use and reproductive behavior, yet, paradoxically, its numbers consistently are surpassed by populations of most other prairie-nesting ducks of North America. Many aspects of Redhead biology are well known: e.g., timing and routes of continental migration, courtship behavior, and pairing chronology (Weller Weller 1964a , Weller 1965b , Weller 1967a ; Johnsgard 1965 ; Bergman 1973 ); nesting ecology, reproductive biology, breeding habitat, and brood parasitism in Utah, Iowa, Manitoba, Montana, and North Dakota ( Williams and Marshall 1938 ; Low 1945 ; Weller 1959b ; Lokemoen Lokemoen 1966 , Lokemoen 1991 ; Kantrud and Stewart 1977 ; Sorenson 1991 ; Sayler 1996 ). Recent advances have been made in estimating survival of Redhead ducklings and females ( Yerkes 2000a , Arnold et al. 2002 ); time-activity budgets in winter in Texas, Louisiana, and Tamaulipas ( Mitchell et al. 1992 , Michot et al. 1994b , Woodin 1994 , Adair et al. 1996 , Vázquez et al. 1996 ); foods and foraging ecology of breeders ( Bartonek and Hickey 1969a , Noyes and Jarvis 1985 , Jarvis and Noyes 1986 , Woodin and Swanson 1989 , Kenow and Rusch 1996 ), of postbreeding birds on Manitoba lakes ( Bailey and Titman 1984 ), and of wintering birds in Texas and Louisiana ( Mcmahan 1970 , Cornelius 1977 , Michot and Nault 1993 , Mitchell et al. 1994 , Woodin 1996 ).