Temporal changes in the diet of Tufted Ducks Aythya fuligula overwintering at Lough Neagh

Numbers of Tufted Ducks Aythya fuligula wintering at Lough Neagh declined dramatically following the winter of 2000/01. The abundance and biomass of benthic macroinvertebrates, their main food source, declined significantly between the winters of 1997/98 and 2010. Therefore, information on recent diet was required to determine if there had been any significant changes before and after the observed declines in numbers of both macroinvertebrates and birds. Here, we used oesophageal content analysis to characterise the contemporary diet of Tufted Ducks at Lough Neagh during 2010-12. Out of 75 shot ducks, only three individuals had prey items in their oesophagi while all four ducks that accidentally drowned in gill nets contained prey items. Oesophageal contents were then compared with data collected during a study conducted in the late 1990s. Contemporary diet of Tufted Ducks was dominated by Asellus aquaticus (48%), but molluscs (14%), grain (13%) and chironomid larvae (11%) were also consumed. Between 1998-99 and 2010-12, the contribution of Asellus aquaticus to the diet significantly decreased while the proportions of chironomid larvae, grain, Gammarus spp. and Mysis spp. increased. Alternative methods of dietary analysis, for example stable isotope analysis, are recommended in future studies of diving duck diet at Lough Neagh.