Nest‐Box Use by Wood Ducks and Black‐Bellied Whistling Ducks in Coastal South Carolina

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ABSTRACTWe surveyed nest‐structure use by sympatric nesting wood ducks (Aix sponsa) and black‐bellied whistling ducks (Dendrocygna autumnalis) across coastal South Carolina, USA, in 2016–2017. Of 718 nest boxes surveyed cumulatively in 2016 and 2017, 61% were used by wood ducks and 15% by black‐bellied whistling ducks. Lower nest‐box use by whistling ducks was related to recent arrivals and breeding by the species in South Carolina. Nest‐box use by wood ducks was 6% greater for every 1,000‐cm3 decrease from the mean internal box volume of all boxes monitored, whereas use by black‐bellied whistling ducks was 20% greater for every 1,000‐cm3 increase from the mean internal volume of all boxes. Box use was 15% and 11% greater by wood ducks and black‐bellied whistling ducks, respectively, for every 10% decrease from the mean percent canopy cover of all nest boxes. Nest‐box use by black‐bellied whistling ducks was 18% and 10% greater for every 10‐cm increase from the mean distance from the base of a box's entrance vertically to the ground or water and every 10‐m decrease from the mean distance to the nearest box for all boxes monitored, respectively. Our results suggested nest boxes with internal volumes of ~15,000–31,000 cm3 were most used by wood ducks, but the conventional nest box with an internal volume of 34,375 cm3 and internal dimensions of 25 × 25 × 55 cm accommodated wood ducks and black‐bellied whistling ducks, and can be deployed where the species are sympatric. However, where black‐bellied whistling ducks occur, the diameter of an entrance hole for nest boxes should be 13 cm to allow passage by the larger bodied species. We suggest a need for research to estimate recruitment rates for box‐nesting females and cost effectiveness of box programs based on female recruitment. © 2020 The Wildlife Society.