Using a Three-Isotope Bayesian Mixing Model to Assess The Contribution of Refuse Dumps in The Diet of Yellow-Legged GullLarus michahellis

Abstract

Summary. The yellow-legged gull Larus michahellis is usually considered as an opportunistic species that depends on food derived from anthropogenic activity, such as garbage and fishery discards. However, although it has become a problematic species in many Mediterranean countries, there is still no information about its status in Tunisia. The aim of this work was to assess the differential use of marine and terrestrial resources by the yellow-legged gulls breeding in an urban area on Chikly Island. Dietary reconstructions were performed through the analysis of regurgitates and δ13C, δ34S and δ15N of fledgling's feathers. Contrary to most Mediterranean breeding colonies, and to our expectations, the mixing model showed that yellow-legged gulls from Chikly are above all marine foragers. Whereas the Lake of Tunis was the principal source of food in 2005 and 2007, chicks from 2006 were fed mainly with prey from the Gulf of Tunis. Although the Gulf is located further from the breeding colony and has less fish...