Long-term declines in nest success of prairie ducks

Increased predation on nests of ducks in prairie uplands, as a result of habitat alteration, has been hypothesized to cause decreased nest success and population sizes. We tested whether, and by how much, nest success declined using data compiled from 37 studies conducted between 1935 and 1992 at 67 sites in the Prairie Pothole Region of Canada and the United States. Nest success declined (P = 0.0002) over time, but time explained only 10% of the variation; precipitation (P = 0.79) did not account for additional variation in nest success. Nest success declined at similar (P = 0.13) rates among 5 species, but late nesters (gadwall [Anas strepera], blue-winged teal [A. discors], and northern shoveler [A. clypeata]) had higher success (P = 0.004) than early nesters (mallard [A. platyrhynchos], and northern pintail [A. acuta]). Populations of gadwalls and northern shovelers, however, have not declined, indicating that declines in nest success may not be related causally to population change. Long-term population declines in blue-winged teal, northern pintails, and mallards coincide with large-scale temporal declines in nest success. Declines in nest success were parallel in parkland and grassland regions, suggesting a causal agent (or agents) that act(s) at a broad scale, despite inherent differences in the composition of the predator communities and habitats between regions.