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

We 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.