Stable Isotope Signatures Reveal Cryptic Differences in Diet of Sociable Weavers

Foraging habits of animals are a critical component of their ecology; however, estimates of feeding that rely solely on observation may not detect all of the factors that affect foraging decisions. Importantly, few studies have examined the influence of sociality on dietary regimes in avian species. The stable isotope ratios of carbon (δ¹³Q and nitrogen (δ¹⁵N) were used to assess the foraging habits of Sociable Weavers (Philetairus socius) at a field site in Namibia. Sociable Weavers were sampled from three different nests, at two different time points over the course of a year. We found significant differences in stable isotope composition between nests, and subsequently compared the isotopic profile to the isotopic profile of the preferred food item. Isotopic structuring between nests suggests that sociality may constrain foraging decisions and could be a common feature of species of animals where foraging groups are temporally stable. We also found that larger nests are more isotopically similar to the preferred foraging source, and thus larger populations may be supported by nearby foraging resources.