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Mallard Recruitment in the Agricultural Environment of North Dakota

Abstract


Recruitment of a mallard (Anas platyrhynchos) population was assessed on a 10,041-km2 study area in central North Dakota during 1977-80. We equipped 338 hens with radio transmitters and monitored them during the breeding season. Two hundred thirty-five of these hens furnished data reported here. Habitat use, nest site selection, fate of nests, and the rate of renesting were measured. Survival of hens during April-September and survival of young were determined. There was a high negative correlation between nest initiation date and mean April or May temperature. Hens selected nest sites most frequently in grassland and least frequently in cropland, but habitat use compared to availability indicated preference for road right-of-way and odd areas of cover and rejection of cropland. Use of other habitats was in proportion to their availability. Nest success was only 8% during the study. Hen success, a function of nest success and renesting rate, averaged 15% and varied among years because of increased renesting in wet years. In all years, 2-year-old and older hens were twice as successful as first-year nesters. Nesting effort was correlated with water conditions as derived from aerial photographs. April-September survival of hens averaged 80% because predation was heavy when hens were on nests. Only 74% of the hens that hatched a clutch were observed later with at least 1 surviving duckling. On average, hens in the spring population recruited only 0.27 young females to the fall population. Based on this recruitment estimate, published survival estimates, and a model previously developed for a closed population, we predict a 20% annual population decline. Nest success of 15% and a resulting hen success of 31% would be required for a stable population. The results suggest that the population on the study area is not maintaining itself but is being supplemented by pioneering birds. A serious recruitment problem has resulted from nest predation. Additional research is needed to determine the geographic extent of the problem. If the problem is widespread, management techniques must be devised to overcome nest destruction, mortality of hens, and mortality of ducklings.
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