Addressing variability in estuarine food density for American black ducks

Abstract

ABSTRACTHabitat limitation and availability of food energy may be the cause of decline in American black duck (Anas rubripes) populations. Estimating food availability is a critical step in developing winter carrying‐capacity estimates for black ducks. Recent research has estimated the biomass and energy supply of winter black duck foods in coastal marshes using a single‐core sampling method, but estimates had large variability. We tested whether taking bulk core samples (i.e., homogenizing multiple core samples and subsampling a single core from it) at the same location (vs. a single core sample) would alter the mean and variance in food estimates in 7 different landscape–vegetation types (hereafter, habitat types: mudflat, subtidal, low marsh, high marsh, quasi‐tidal pools, a tidal impoundment, and a freshwater impoundment) in coastal New Jersey, USA, during 2011. In all but one habitat type, there were no differences in the mean biomass or the mean energy density estimates for the single core samples and the bulk core samples, across all food types. Variance was reduced in subtidal and quasi‐tidal pool habitats, but variance increased in tidal impoundments. Assessing time and cost‐efficiency of bulk samples over single samples, cost per sample increased 4–12%/core. Because we observed little difference in food biomass, energy, and their respective variance estimates between single and bulk methods, while recording a slightly greater cost, we recommend researchers use the single‐core sampling method to save both time and money. Further reductions in variance will likely need to be achieved through increased sample sizes. © 2016 The Wildlife Society.