Dabbling Duck Recruitment in Relation to Habitat and Predators at Union Slough National Wildlife Refuge, Iowa.

摘要

The influence of habitat quality and predation on nesting success and recruitment of dabbling ducks (Anatini) was studied at Union Slough National Wildlife Refuge in north-central Iowa, 1984-85. Blue-winged teal (Anas discors) and mallards (A. platyrhynchos) made up 91-93% of the breeding population. Pair numbers increased from 155 (27/sq km of wetland) in 1984 to 336 (58/sq km of wetland) in 1985 when local drought conditions prevailed. Water control structures maintained good wetland conditions in both years. Reflooded wetlands were more attractive than continuously and deeply flooded wetlands. The authors found more nests in 1985 (0.6/ha) than in 1984 (0.4/ha). Nest densities in uplands reflected numbers of pairs using the adjacent wetland. Hens selected nesting sites on the basis of nesting-cover quality. Mallards and blue-winged teal preferred nest sites that were most available in grass-legume fields. Overall nest success (Mayfield 1961) averaged 11.9%. Variation among fields in the quality of vegetation had no effect on nest success variability. Mammals caused most of the nest failures (82%); the primary predator was the red fox (Vulpes vulpes). Although nest success was highest in the few areas without red fox, it only occurred in fields with low nest densities.