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Female Redheads (Aythya americana) are known to deposit eggs in nests of Mallards (Anas platyrhynchos). Joyner (J. Wildl. Manage. 40:33-38, 1976) attributed a high rate of Redhead parasitism on Mallard nests at Farmington Bay, Davis Co., Utah, to crowding of host and parasite into the same habitat. Weller (Ecol. Monogr. 29:333365, 1959) stated that at Knudson Marsh, Utah, only a few deep channels and patches of water were suitable for feeding and courtship by Redheads, and nests of other ducks located near those areas were heavily parasitized; nests farther from the shore were parasitized less often. Redhead nest parasitism resulted in reduced host clutch-size (Weller 1959), displaced and broken host eggs (Joyner 1976) and increased nest abandonment (Ryder, Trans. N. Am. Wildl. Nat. Resour. Conf. 26:134-146, l6l).