Despite the fact that Lesser Scaup and Ring-necked Ducks are closely related and nest in similar habitats, the two species have inverse population trends. To evaluate the hypothesis that the difference in trends could be related to differences in reproduction, we compared nesting success of sympatric Lesser Scaup and Ring-necked Ducks in parkland habitat near Erickson, Manitoba. Data supported a model that allowed nest survival to differ by species more strongly than a model that did not. Daily survival rate of Lesser Scaup nests (0.941) was lower than that of Ring-necked Ducks (0.969). All Ring-necked Ducks nested over water, but only 57% of Lesser Scaup nested over water. Further, we found some evidence that nest survival was better over water than in upland locations. If our observed pattern of differential nesting success between species holds across broader areas, it may explain why Ring-necked Ducks are increasing across North America while Lesser Scaup populations are declining.
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Vol. 74 • No. 3