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There has long been interest in the influence of predators on prey populations, although most predator-prey studies have focused on prey species that are targets of directed predator searching. Conversely, few have addressed depredation that occurs after incidental encounters with predators. We tested two predictions stemming from the hypothesis that nest predation on two sympatric freshwater turtle species whose nests are differentially prone to opportunistic detection-painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina)-is incidental: (1) predation rates should be density independent, and (2) individual predators should not alter their foraging behavior after encountering nests. After monitoring nest survival and predator behavior following nest depredation over 2 years, we confirmed that predation by raccoons (Procyon lotor), the primary nest predators in our study area, matched both predictions. Furthermore, cryptic C. picta nests were victimized with lower frequency than more detectable C. serpentina nests, and nests of both species were more vulnerable in human-modified areas where opportunistic nest discovery is facilitated. Despite apparently being incidental, predation on nests of both species was intensive (57% for painted turtles, 84% for snapping turtles), and most depredations occurred within 1 day of nest establishment. By implication, predation need not be directed to affect prey demography, and factors influencing prey crypsis are drivers of the impact of incidental predation on prey. Our results also imply that efforts to conserve imperiled turtle populations in human-modified landscapes should include restoration of undisturbed conditions that are less likely to expose nests to incidental predators.

drogen atoms were placed in calculated positions (C-H = 0.95 Á) and were constrained to ride on their respective carbon atoms.The absolute configuration was assigned by first assuming the R,R configuration. Six final cycles of least-squares refinement converged at R, = 0.0448 and R2 = 0.0493. Anomalous dispersion due to Mo was included in the calculation. The alternate hand of the structure was then refined to convergence from the same starting point, again with six cycles of least-squares refinement, giving a final R, = 0.0466 and R2 = 0.0515. Thus the original assignment of configuration, depicted in Figure 1, was shown to be correct.

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