Interpreting Evidence of Depredation of Duck Nests in the Prairie Pothole Region
GEOLOGICAL SURVEY JAMESTOWN ND NORTHERN PRAIRIE WILDLIFE CENTER
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We examined patterns of depredation of duck nests by 9 species and 2 congeneric species-groups of predators in the Prairie Pothole Region coyote Canis latrans, red fox Vulpes vulpes, raccoon Procyon lotor, striped skunk Mephitis mephitis, American badger Taxidea torus, mink Mustela vison, weasels ermine M. erminea and long-tailed weasel M. frenata, Franklins ground squirrel Spermophilus franklin ii, black-billed magpie Pica pica, American crow Corvus brachyrhynchos, and gulls ring-billed gull LARUS DELAWARENSIS and California gull L. californicus. We discuss factors affecting amount and types of evidence of depredation left by predators at duck nests, including characteristics of eggs and nest sites, behavior of ducks and predators, anatomy and size of predators, and effects of other animals. Accounts of depredation patterns of individual predator species and species-groups are provided and include summaries of positive and negative indicators of depredation. Information presented is mostly from studies we conducted during 1972-92, which involved offering duck eggs to captive and free-ranging predators and monitoring responses by direct observation, time-lapse camera, or revisiting sites. Variables of depredation were quantified on nest depredation records and included disturbances of eggs, ground surface, and nest material. Patterns of depredation of some predator species varied little e.g., red fox but patterns of others varied greatly e.g., coyote. There was much overlap of patterns among some predator species e.g., Franklins ground squirrel, weasels. A format with instructions for preparing nest depredation records is provided. Recommendations for interpreting depredation records are discussed. We applied recommendations to 389 depredation records from waterfowl production areas in Minnesota, North Dakota, and South Dakota and discuss outcomes of that exercise.