Compensatory predation on ducks in a complex prairie food web

Prairie ducks were studied in the context of complex food webs to understand the influence of predation on local duck abundances. I tested the hypothesis that raptors increase consumption of ducks upon decreased consumption of duck eggs by mammals (compensatory predation). I predicted (1) greater abundance and reproductive success of raptors (numerical responses) and (2) greater proportion of ducks in the diet of raptors (functional response) where mammalian predators were reduced relative to where they were more abundant. Roadside surveys, spot counts and nest searches were used to evaluate the strength of numerical responses in raptors. I tested for a functional response in red-tailed hawks Buteo jamaicensis using stable isotope analysis of C (carbon) and N (nitrogen) on blood components of hawk nestlings and prey items. Compensatory predation on ducks by raptors appeared weak overall. The efficacy of managing predators to increase duck abundance depends on the relative influence of predation, food resources and abiotic factors on duck survival.