Prey Composition of Great Crested Grebe (Podiceps cristatus) and Red-Throated Diver (Gavia stellata) in Freshwater Reservoirs during Migration

Abstract

The diet composition and prey length of the Great Crested Grebe (Podiceps cristatus) and the Red-throated Diver (Gavia stellata) co-occurring in late autumn in two reservoirs was studied. Their diet was analyzed based on carcasses from incidental mortality of individuals in fishery gill net surveys in two different freshwater reservoirs (one deep, one shallow) in southern Poland during autumn migration (October - December). Five fish species were identified in the diet of the Great Crested Grebe and nine fish species were identified in the diet of the Red-throated Diver. The proportion of a particular fish species in diet was different between the studied bird species. The ruffe (Gymnocephalus cernua) was the most common prey in the diet of the Great Crested Grebe at both reservoirs. The diet of Red-throated Diver was dominated by roach (Rutilus rutilus) at the deep reservoir and the zander (Sander lucioperca) at the shallow one. The Red-throated Diver consumed larger fish than the Great Crested Grebe at both reservoirs.