Some Aspects of Breeding Biology of the Blue-Winged Teal

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 45.3øF 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 1962 and 1963 are graphed in Figures 1 and 2. Daily records kept by Nan Mulder at Delta show that the temperatures there are similar to those at Winnipeg.METHODS In the first summer in the field, I searched for nests within approximately a one-mile radius of the research station; three-fifths of the area was covered by water.In order to flush hen teal and thus locate their nests, we used rock-filled oil cans attached to a rope which was dragged between two men or tractors.Laths or bamboo poles were used to beat the heavier vegetation.During the 1962 nesting season the same area was covered but we intensified our efforts in the area immediately around the headquarters.Weller (1964).Teal normally lay one egg a day, as do other dabbling ducks.Usually the egg is laid before 1000 hours.Thus, when a female was flushed from a nest with an incomplete clutch after 1000, I arbitrarily considered that the egg for that day had been laid.Although this procedure may not be completely accurate, it does provide a reasonable demarcation from which' the date of clutch initiation can be obtained by backdating one day for each egg present in the nest. Date o/ nest initiation.---A review of the reproductive cycle of waterfowl has been given byWhen the eggs had already been incubated, the stage of incubation was discerned by candling the eggs.By backdating the number of days that 389