Fig. 3. Predicted duck nesting success and 95% CIs (dotted lines) in the Aspen Parkland of Alberta, Canada, in relation to nest-site vegetation density and field residual cover (RC), based on the most parsimonious nesting success model DSR (nest-site vegetation density*residual cover; n = 633 nest-fate intervals). Nest-site vegetation density was quantified as the mean of four visual obstruction measurements taken at each nest in each of the cardinal directions. Nest-site vegetation density and RC were not correlated (Pearson’s product-moment correlation, r < 0.01, P = 0.83). The horizontal dashed line represents the hypothesized threshold level of nesting success (0.15) believed necessary to maintain a mallard population (Cowardin et al. 1985, Klett et al. 1988). The vertical line represents the average nest-site vegetation density (2.2 dm) during the study.