Box-nesting Wood Ducks and Black-bellied Whistling Ducks in Coastal South Carolina

Installation and maintenance of artificial nesting structures are established practices for increasing production of secondary cavity nesting waterfowl, especially wood ducks (Aix sponsa). In South Carolina, tens of thousands of nest boxes have been erected on public and private lands. Ad- ditionally, since the early 2000s, black-bellied whistling ducks (Dendrocygna autumnalis) have expanded their range into South Carolina and now are nesting sympatric with wood ducks in boxes. We conducted a survey of 364 and 354 nest boxes in 2016 and 2017, respectively, across the Ashepoo, Combahee, and Edisto river (ACE) and the Santee Rivers Delta and Winyah Bay (SRDW) basins in coastal South Carolina. We did not detect a differ- ence in frequency of nest box use between basins by wood ducks (~61%) or black-bellied whistling ducks (~15%). We believe low use of nest boxes by black-bellied whistling ducks was due to their recent colonization of South Carolina. Nest success (i.e., ≥1 egg hatched) across both years was 65% for wood ducks and 51% for black-bellied whistling ducks. Based on presence of egg-shell membranes or ducklings counted in boxes, we estimated an av- erage of 10.2 wood duck (SE = 0.3) and 9.5 black-bellied whistling duck (SE = 0.8) ducklings exited successful nests. We used our reproductive data and a published recruitment rate for yearling female wood ducks returning to nest boxes in South Carolina (6.8%) to cost-evaluate wood duck recruitment from boxes. Assuming 2.8 female recruits produced per box over a 20-year box life, cost per female recruit per box was only ~1/3 the lifetime cost of a box and its maintenance. Our study rationalized the need for regional and cross-flyway investigations of recruitment by wood ducks and other ducks nesting in artificial structures and natural cavities.

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