Use of anthropogenic debris as nesting materials in a south-Mediterranean yellow-legged gull (Larus michahellis) breeding colony in relation to their environmental availability.

The use of plastics and other anthropogenic debris (AD) as nesting materials by the yellow-legged gull Larus michahellis (YLG) has been previously reported in different north Mediterranean and Atlantic breeding colonies. This behavior is also suspected to widely occur in south-Mediterranean areas, and possibly to a greater extent because of high AD availability related to inefficient waste management systems, but data are lacking. The aim of our study was therefore to investigate AD incorporation into YLG nests in a southern Tunisian breeding colony and determine to what degree this integration was associated with debris availability in the environment. We examined nest materials from 232 nests and evaluated AD pollution within the colony area using transect sampling. Eighty-eight percent of sampled nests contained AD which accounted for 3% of the weight of nest materials. Although plastics were the most common AD category, representing 78% of recorded AD items and 71% of AD weight, there was no evidence of a preference for plastics over the other categories. Indeed, AD of different categories were incorporated into nests in accordance with their availability in the surroundings. However, our results did suggest a preference towards white-clear AD, a pattern that could be driven by the probable dietary origin of these materials. Overall, we report a level of AD in YLG nests that is among the highest found in the Mediterranean, and we suggest that the YLG may be a facilitator of Mediterranean coastal pollution by carrying human waste elements into natural areas.