Relative success of overwater and upland mallard nests in southwestern Manitoba

Overwater and upland Anas platyrhynchos nests were monitored in SW Manitoba. Nest success estimates were higher for overwater nests (43.9%) than for upland nests (12.2%). Overwater nests were more likely to be parasitized (primarily by redheads Aythya americana) than were upland nests (11% vs. 0% parasitized, respectively). Parasitized nests contained an average of 1.2 fewer mallard eggs and had 23% lower egg success than unparasitized nests, but these costs were not sufficient to offset the large advantage in nest success that was associated with overwater nesting. A large fraction of the local mallard population was thus nesting successfully in a habitat that is not searched during traditional nesting studies. -from Authors