Evaluating deterrents to reduce depredation of wood duck eggs in nest boxes

Abstract Wood ducks ( Aix sponsa ) are secondary natural cavity‐nesting species that also nest in artificial nest boxes. Since the early 20th century, nest boxes have been widely deployed in North America to increase nesting sites for wood ducks and bolster production. Equipping nest boxes with a predator guard beneath the box is a common practice to deter climbing predators from accessing boxes; however, there is no device to repel avian predators. We found that eastern rat snakes ( Pantherophis alleghaniensis ) and woodpeckers (Picidae) were primary predators of wood duck eggs in boxes in North Carolina and South Carolina. Accordingly, we designed experiments to deter snakes and woodpeckers using a commercial brand of snake repellent pellets and a plastic raptor decoy, respectively. Male and female snakes that accessed boxes averaged 1.4 m (SE = 2.0 cm) in length. Digital camera data indicated that snakes climbed nest box posts and thrust their anterior body atop predator guards to continue their ascent into the box. We recorded 671 nest failures of which rat snakes accounted for 39.9% ( n = 268) and woodpeckers 22.4% ( n = 150). Snakes consumed ≥649 eggs, observed as protuberances in their stomachs. Our experiment showed that commercial snake repellent pellets did not deter snakes ( P = 0.957). Placing a plastic hawk decoy atop nest boxes when females were incubating ≥12 days increased nest survival during the incubation stage ( P = 0.001). Wood duck nest boxes at our study sites may be experiencing increased nest predation by rat snakes due to poor maintenance and installation of predator guards. Rat snakes and woodpeckers may be depredating wood duck eggs in the southeastern United States at unknown rates, potentially decreasing production and recruitment from these structures.