Montana Field Guide

Species sexually dimorphic. Males in alternate plummage have gray brown body with a white abdomen and black rump. Black and chestnut portions of some inner median and lesser wing-coverts, slate gray bill, and yellow legs. Females overall brownish color with distinctive bill color (orange yellow with dark longitudinal midsection and gray black lateral spots), and presence of white speculum.

Normal migration periods in the Bozeman area are from March 20 to May 20 and from October 1 to November 10, with peak numbers reached on April 20 and October 15 (Skaar 1969).

At Bowdoin National Wildlife Refuge Gadwall nest density was highest in saline lowlands, followed by dense nesting cover, panspots, and silty/ shallow clay. Nest success was highest in saline lowlands, then clay, panspots, silty sites and dense cover (Holm 1984).

Diet consists mainly of submerged aquatic vegitation, seeds and aquatic invertibrates.

The primary cause of nest loss was depradation (67%) from (in order of importance) striped skunk, red fox, coyote, Richardson's ground squirrel, racoon, avian, and mink. At Freezeout Lake, skunks were the major cause of unsuccessful nests.

The brood size was 6.2 in rest-rotation grazing pastures in north-central Montana. Nesting occurred from late May to the third week of August. At Freezeout Lake, island nesters were most successful (75%). The average of all types was 28%. The average clutch size was 11.9 and hatching dates were from May 21 to August 10.