Abstracts

Presented by Gillie D. Croft - Email: gcroft@clemson.edu

We surveyed nest-structure use, duckling production, and other metrics of reproductive ecology of wood ducks (Aix sponsa), black-bellied whistling ducks (Dendrocygna autumnalis), and hooded mergansers (Lophodytes cucullatus) during a landscape-scale study across coastal South Carolina in 2016-2017. Wood ducks used the greatest proportion of >350 monitored boxes (61%), followed by black-bellied whistling ducks (15%) and hooded mergansers (<1%). Wood ducks began nesting in January, before most black-bellied whistling ducks did in May. Peak nesting for wood ducks occurred in March-April for wood ducks and June for black-bellied whistling ducks. Based on phenology by these species, we speculate little competition occurs for boxes between them. Additionally, average percent use, numbers of eggs laid, and number of ducklings exiting from boxes were greater for wood ducks than black-bellied whistling ducks, because the latter species is not breeding abundantly yet in South Carolina (61% vs. 15% box use, 8 vs. 2 eggs, 5 vs. 1 duckling[s]). Our results indicated size of the conventional nest-box described by F.C. Bellrose was used by both species and therefore can be deployed where these species co-exist. However, where black-bellied whistling ducks are becoming increasingly abundant, we suggest nest-box entrances should have 5-inch diameters to facilitate use by this larger duck species. Lastly, we assessed cost of female wood duck recruits from nest boxes, based on expenditures to fabricate boxes, annual maintenance, an assumed longevity of 20-years for an annually maintained box (total=$143.23/box[U.S.2018]), reproductive metrics from our study, and a wood duck female recruitment rate of 6%. The cost per female wood duck recruit was $59.68, which was 2.4 times less than the cost of the box, its mounting-structure, predator-shield, and maintenance over 20-years ($143). Therefore, nest boxes in our study areas seem cost-effective, but female recruitment rates should be estimated cross-flyways to determine if nest-box populations are self-sustaining and cost-justified.