Foraging ecology of the Great Crested Grebe (Podiceps cristatus L.) at a mesotrophic-eutrophic reservoir

The foraging ecology of the Great Crested Grebe wasstudied at Dobczyce Reservoir in southernPoland. The mean diving frequency of grebes withoutyoung was 19.3 h^–1, while grebes with young dived onaverage 32.5 h^–1. The mean number of apparent prey caughtby grebes without young was 0.5 fish h^–1. Birds with young caught a greater number, on average4.5 fish h^–1. Probably, birds fishing forthemselves ate much prey underwater. The total lengthof the fish consumed by adult grebes was on average10.0 cm. Adults ate larger fish in the breeding seasonthan in the autumn migration period. Young birds werefed fish about 8.3 cm long. More than 50% of preywere bleak. The mean success of dives of birds withoutyoung was 3.3% and for individuals with young 14.8%.A comparison of the weight of the daily food demandwith the weight of fish brought to the surface showed that it was 70% lower than the dailyfood demand. The poor relation between prey size anddiving success shows that grebes can eat both small andlarge fish below the water surface.