A medium-sized (41.9 to 43 cm, 730 to 850 g) black and white diving duck, one of the most abundant and widespread of North American ducks. Adults sexually dimorphic most of year. Male in Definitive Alternate plumage characterized by slaty blue bill; black head with purplish gloss; black neck, breast, and upper mantle; white flanks and belly; gray-flecked lower mantle; and black vent and undertail region. Female is fuscous to chocolate brown with white patch of varying size at base of bill (sometime broken into patches of white); upperparts darker; wing-coverts flecked with gray; bill dark gray. Iris color in males is brilliant yellow, but in females varies with age from olive brown to olive or brownish yellow (Austin et al. 1998).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.
Western Hemisphere Range
Normal migration periods in the Bozeman area are April 10 to May 25 and October 1 to November 20, with peak numbers on April 25 and October 25 (Skaar 1969).
In the Bozeman area, habitat is generally restricted to lakes and ponds (Skaar 1969). Throughout fall and winter this species forms large flocks on rivers, lakes, and large wetlands. Pairs and broods typically associated with fresh to moderately brackish, seasonal and semipermanent wetlands and lakes with emergent vegetation such as bulrush, cattail and river bulrush (Austin et al. 1998).
Mainly aquatic invertebrates such as insects, crustaceans, and mollusks. Seeds and vegetative parts of aquatic plants are important in certain areas (Austin et al. 1998).
At Bowdoin National Wildlife Refige, 25,000 were seen in November 1949. The major cause of unsuccessful nests at Freezeout Lake was skunk predation.
Individuals form new pair bonds during spring migration each year. Female builds nest on the ground near or over water, as well as in uplands, unlike other diving ducks. Eggs are elliptical to nearly oval in shape. The color is pale olive or greenish buff to dark olive buff. Most clutches have 8 to 10 eggs (Austin et al. 1998). Actual nest records are scattered from mid-May to August 10. Hatching dates at Freezeout Lake were from June 1 to August 20. Birds nesting on islands were more successful (60%) than those in other habitat types (average of all was 23.5%). Average clutch size was 9.5.