. The Canadian field-naturalist. 56 The Canadian Field-Naturalist Vol. 93 LAKE MANITOBA. PAIRS OF YELLOW SAOOLED MALLARDS I KM FiGi RE 1. Map ol the Delta Marsh illustrating the study areas and the location of marked females established outside the release sites in 1973. lished at Aikens Bay, a area, 8 km E of Delta. The aquatic and upland habitat at Aikens Bay was managed for waterfowl (mainly by water-level regulation) and was considered to be high quality. An unknown number of wild Mallards occupied each release site prior to stocking. A area at Cooks Creek Meadow, km E
. The Canadian field-naturalist. 56 The Canadian Field-Naturalist Vol. 93 LAKE MANITOBA. PAIRS OF YELLOW SAOOLED MALLARDS I KM FiGi RE 1. Map ol the Delta Marsh illustrating the study areas and the location of marked females established outside the release sites in 1973. lished at Aikens Bay, a area, 8 km E of Delta. The aquatic and upland habitat at Aikens Bay was managed for waterfowl (mainly by water-level regulation) and was considered to be high quality. An unknown number of wild Mallards occupied each release site prior to stocking. A area at Cooks Creek Meadow, km E of Delta, was chosen for a control (, no birds released) in 1972. That area is typical marsh habitat. In 1973 water levels were lower than usual on parts of the Delta Marsh. Wind tides from Lake Manitoba maintained water levels in the larger bays, but lack of precipitation left many nearby potholes and shallow marshes dry. Precipitation at Portage la Prairie was cm lower than the long-term mean for 6 mo prior to 30 March 1973 (Atmospheric Environment Monthly Reports). Methods Ducklings were hatched in an incubator, from eggs taken from a captive flock originating from eggs gathered in the wild and hatched at Delta. Ducklings were hand-reared (Ward and Batt 1973) until 4-5 wk of age before release. Each duckling was fitted with an individually num- bered plastic nasal saddle and a standard Fish and Wildlife Service leg band immediately prior to release. Birds were liberated in groups of 10-15 throughout all wetlands on the study areas. In 1971, 456 females and 180 males were released at the Diversion. In 1972, 503 females and 34 males were liberated at Aikens Bay and 245 females at the Diversion site. Mallard breeding densities were estimated by checking on foot each wetland on the study area. Each Mallard observed was checked for a nasal saddle. Counts were conducted as suggested by Dzubin (1969). A roadside transect was run 5-6 times a week on the Diver
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