Kleptoparasitism as an important feeding strategy for migrating Wigeon Anas penelope

Abstract

This study investigated Wigeon Anas penelope feeding strategies adopted at two wetlands in response to differing macrophyte communities, water levels and levels of disturbance. Wetland I contained a diverse macrophyte community dominated by Beaked Tasselweed Ruppia maritima in shallow areas and stoneworts Chara sp. in deeper water. Wigeon did not feed on the Ruppia maritima but kleptoparasited Coot Fulica atra foraging on Chara. In this case, kleptoparasitism was related to food quality, with Ruppia maritima having lower nutritional value than Chara which contains high quantities of easily digestible non-structural carbohydrates. Thus Wigeon ignored an available but low quality food source in favour of kleptoparasitising Coot to obtain higher quality Chara. Wetland II had abundant food resources dominated by Spiral Tasselweed Ruppia cirrhosa in both shallow and deeper areas but hunting was permitted, causing shoreline disturbance to feeding Wigeon. Before the hunting season, Wigeon fed primarily in single species flocks in shallow water using pecking and head-dip feeding methods. When the hunting season opened, those Wigeon remaining on the site moved to deeper waters and fed exclusively by kleptoparasitising Mute Swans Cygnus olor. Wigeon must feed for most of the day to meet their energy requirement and this study shows that kleptoparasitism is one of the strategies that they use to maintain food intake rates under different foraging constraints.