US Geological Survey


Date of this Version



Published in THE WILSON BULLETIN Vol. 93, No. 4, December 1981.


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).