A Comparison of Sampling Methodologies to Improve Estimates of Available Food for American Black Ducks in New Jersey

Potential habitat limitations and availability of food energy may be the cause of decline in American black duck (Anas rubripes) populations. It is critical that food availability estimates are determined, in order to develop a carrying capacity estimate for black ducks, in the future. Research was recently conducted to estimate the biomass and energy supply of black duck foods using a single core sampling method, but high variance was found for these estimates. Our goal was to improve estimates of available foods for the American black duck in New Jersey by comparing a single core sampling method and a multiple core sampling method. Core samples were collected from 7 habitat types (mudflat, subtidal, low marsh, high marsh, quasi-tidal pools, east pool tidal impoundment, and west pool freshwater impoundment) in coastal New Jersey. There were no differences in the mean weight or the mean energy content for the single core samples and the multiple core samples, across all habitat types, for all black duck foods, black duck animal foods, or black duck seed foods. The only exception was the east pool impoundment, where the multiple sampling method found more animal foods (single: 0.005853g ± SE 0.000930 vs. multiple: 0.011661g ± SE 0.002376) and energy available (single: 0.004110 kcal ± SE 0.000642 vs. multiple: 0.008189 kcal ± SE 0.001739) than the single sampling method. Data was averaged between methodologies and we compared biomass weight and energy between habitats. Overall, since no differences existed, we recommend continuing to use the single core sampling method to save both time and money for future researchers.