Montana Field Guide

An exclusively North American species. Gregarious and highly visible during the nonbreeding season. The Canvasback is a large diving duck. Male (51-56 cm/863-1589 g) slightly larger than female (48-52 cm/908-1543 g). Thin wedge-shaped head sloping upward from tip of long bill to back of crown and long, stout neck, head held erect. Adult male: rich chestnut red head and neck, black chest, white back and long sloping, blackish bill. Adult female: forehead, crown, nape and upper neck light brown to brownish olive; cheeks, chin and throat whitish buff; lower neck gray-brown, with reddish-brown cast. Mantle and scapulars light gray, lower back and rump grayish; belly white to grayish white; bill nearly black. (Mowbray, Thomas. The Birds of North America, No. 659, 2002).

Normal migration periods in the Bozeman area are from March 28 to May 20 and from September 20 to December 1, with peak numbers on April 15 and October 15.

Breeds in small lakes, deep-water marshes, sheltered bays of large fresh water and alkali lakes, permanent and semi permanent ponds, sloughs, potholes, and shallow river impoundments. In aspen parklands and mixed-grass prairie, prefers wetlands bordered by dense emergent vegetation. In boreal forest, utilizes open marshes. (Mowbray 2002).

Omnivorous. Foods vary depending upon availability. During winter and migration, mainly plants (winter buds, rhizomes, and tubers or aquatic plants. When plant food is limited, may take small clams and snails. (Mowbray 2002).

At Bowdoin National Wildlife Refuge in April 1948, 5000 were seen. At Freezeout Lake, all nests in emergent vegetation were unsuccessful due to flooding.

Monogamous and secretive during the breeding season. Nest is a large bulky structure. May be overtopped by vegetation and may have one or more well-maintained ramps. Eggs are elliptical to elliptical-ovate. Grayish olive or greenish drab in color. Clutch size is affected by egg parasitism. Size is widely variant (2 - 16) as a result. (Mowbray 2002). The nesting period is from late May through July. Hatching at Freezeout Lake was from June 1 to July 31; hatching dates are from May 21 to June 30.