Nest success, climate variability, and population dynamics of prairie ducks in an agricultural landscape

The Prairie Pothole Region in the North American mid-continent has experienced increases in mean annual temperature. In addition, cropland has replaced much of the native grasslands. These changes may have eroded the landscape's capacity to support duck populations. Indeed, nest success of 5 species of common duck species breeding across the Prairie Pothole Region declined from an average of 30% in the mid-1930's to roughly 10% in 1992. I re-examined this decline by compiling recent estimates of nest success for these 5 duck species, and analyzed temporal trends using local regression, and found that, rather than having undergone a monotonic decline, average nest success has fluctuated through time. Further, these fluctuations are not associated with availability of wetlands, which is known to strongly affect population growth rates of prairie ducks. In contrast, nest success has a positive correlation with mean spring temperature. This correlation suggests that climate warming will not deleteriously affect nest success, and may partly explain the temporal fluctuations in nest success. While the assumption that nest success drives population dynamics of prairie ducks is a key tenet of many habitat management programs, it has not been empirically tested. I compared historical records of nest success with observed population growth rates at 3 spatial scales, and found little evidence of a strong link between nest success and population growth rate. These results cast doubt on the common conception that nest success is the major driver of the number of ducks breeding in the prairies. In an effort to relate the population dynamics of ducks to the natural and anthropogenic changes in the landscape, I partitioned the variation in spatial synchrony of the most common duck species to factors relating to variation in wetland availability, distance among sites, and agricultural cover. Synchrony for most species was largely driven by availability of ephemeral wetlands, and decreased with distance among sites. The effect of agricultural cover minor relative to climate and distance, and differed by species. Thus, availability of ephemeral wetlands and dispersal processes, 2 factors over which managers may have little control, largely drive population dynamics of prairie ducks.