Carrying capacity of wintering American black ducks in forested wetlands

Wintering populations of American black ducks (Anas rubripes) have declined throughout their range since the 1950s. Conservation for wintering black ducks is based largely on bioenergetic models of carrying capacity, and managers seek to provide wetlands with sufficient food energy to support target populations. Although the significance of salt marsh to wintering black ducks along the Atlantic Coast is well documented, forested wetlands are also used by wintering black ducks, and yet their foraging value and energetic potential is unknown. Therefore, quantifying the energetic value of forested wetlands is important for accurately estimating the carrying capacity of black ducks. We collected soil core samples from forested wetlands on Prime Hook National Wildlife Refuge, Milton, Delaware in 2014 (n = 46) and Edwin B. Forsythe National Wildlife Refuge, Galloway, New Jersey, USA in 2015 (n = 41) to estimate food biomass and quantify the energetic capacity of forested wetlands representative of the mid-Atlantic region. We estimated the mean energetic value of forested wetlands as 84,667 ± 21,822 kcal/ha. Considering all forested wetlands that are potentially available to black ducks along the mid-Atlantic Coast, we estimated that forested wetlands within a 24.1-km distance from the coast provide between 103,696,524–192,678,224 duck-use days supporting 489,135–908,860 black ducks over the 212 days of winter. Forested wetlands may be an important foraging resource for wintering black ducks, and our estimates of energetic value will help to refine bioenergetic models for black ducks in the Atlantic Flyway. © 2017 The Wildlife Society.