James H. Devries, John J. Citta, Mark S. Lindberg, David W. Howerter, Michael G. Anderson, Breeding-Season Survival of Mallard Females in the Prairie Pothole Region of Canada, The Journal of Wildlife Management, Vol. 67, No. 3 (Jul., 2003), pp. 551-563
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Devries et al. (2003) studied this question.