The Blue-winged Teal (Anas discors) was the subject of one of the first publications dealing with the breeding biology of a species of North American waterfowl (Bennett, 1938). Recent studies of the nesting chronology, clutch size, and incubation period of this species include the works of Hochbaum (1944), Sowls (1955), and Glover (1956). The present paper supplements information on these aspects of breeding biology.
Field work was done during the summers of 1961, 1962, and 1963 at the Delta Waterfowl Research Station (15 miles north of Portage la Prairie, Manitoba) which is adjacent to the Delta marsh at the south edge of Lake Manitoba. The climate in the area is subhumid. The mean annual temperature is 45.3°F and the annual precipitation is 20.1 inches at Winnipeg (60 miles ESE of Delta). The spring warming trend is variable and influences the time of spring arrival and the start of nesting of waterfowl (Sowls, 1955) and, as will be shown, the temperature may also influence the nesting chronology once a species has begun to nest. The daily mean temperatures and the daily lows at Winnipeg for the springs of 192 and 1963 are graphed in Figures 1 and 2. Daily records kept by nan Multer at Delta show that the temperatures there are similar to those at Winnipeg.
