Resource partitioning among five species of waterfowl (Anasspp.) at an autumn migratory stopover: combining stable isotope and mercury biomarkers

Abstract

The Saskatchewan River Delta (SRD) is North America’s largest inland delta and an important stopover site for waterfowl in the Central Flyway. However, little is known about their basic feeding ecology at this site and how species segregate or overlap in resource use. We used stable carbon (δ13C) and nitrogen (δ15N) isotopes and mercury concentrations ([Hg]) in liver tissue to trace use of local nutrient sources by five waterfowl species and tested for differences in diets among species, sexes, and age groups. Macrophytes were the dominant food source for Northern Pintail (Anas acuta L., 1758) and American Wigeon (Anas americana Gmelin, 1789) with median proportions of 0.86 and 0.98, respectively. There was also evidence of partitioning of resources, as Blue-winged Teal (Anas discors L., 1766) and Green-winged Teal (Anas carolinensis Gmelin, 1789) consumed invertebrates, as did a subset of Mallards (Anas platyrhynchos L., 1758), suggesting that these birds might minimize competition for resources during the short staging period in the SRD when waterfowl densities are high. Other isotopes or tracers, such as [Hg] that varied among sources (0.03–0.20 μg·g–1 dry mass) and waterfowl species (0.22–3.19 μg·g–1 dry mass), can be used for further refining dietary estimates.

The Importance of Isotopic Turnover for Understanding Key Aspects of Animal Ecology and Nutrition

“…Differences in the isotopic signature of dietary items require differences in isotopic fractionation, which can result from physical processes (e.g., geographic 2 H gradients) [9,45,46,88], metabolic pathways (e.g., C 3 vs. C 4 plant δ 13 C) [9,12,43], trophic level (e.g., plant vs. consumer δ 15 N) [9,40,44], or biome (e.g., marine vs. terrestrial δ 13 C and δ 15 N) [9,[40][41][42]. Once diet has been established, that information can then be used to answer a wide range of ecological questions, including what resources are used by different species [13,[89][90][91], where individuals move to acquire those resources [92][93][94][95], how energy and nutrients move among trophic levels [34,35,96,97], and how communities and biomes are linked by the flow of energy and nutrients [42,[98][99][100]. The diversity and novelty of these applications contribute to the great popularity of stable isotope-based diet reconstruction methods.…”

Bioacumulación de mercurio y plomo en el pato Dendrocygna autumnalis en la subregión de la Mojana, Colombia

“…Además, los macroinvertebrados de los que se alimenta tienen como fuente alimenticia plantas macrófitas y sedimentos. El proceso de biomagnificación del Hg inicia en los sedimentos, pasando a las macrófitas, y de estas a los macroinvertebrados acuáticos de los que se alimenta D. autumnalis (34). Las concentraciones de Pb registradas en sangre y plumas de D. autumnalis se pueden explicar por la acumulación de Pb en matrices ambientales que sirven como sustrato alimenticio para esta especie como los cultivos de arroz, los cuales requieren altas concentraciones de agroquímicos, que son ricos en metales pesados (35).…”