溜池におけるカンムリカイツブリ(Podiceps cristatus)の給餌生態 : 青森市における観察例

抄録

We studied the feeding ecology of Great crested grebes Podiceps cristatus that were breeding in an irrigation pond; the study was performed during the chick-raising period. The grebes nearly exclusively exploited Stone morokos Pseudorasbora parva and Crucian carp Carassius gibelio langsdorfii and C. cuvieri. While the parents size-selectively used these fishes as food for the chicks, they also exploited seasonally abundant underyearling fishes. Consumable prey size was restricted for the youngest chicks, and the body depth of the fish was the restricting factor for consumption. Stone morokos were an important part of the diet for the youngest chicks, whereas Crucian carp became a more important food item at a later stage. Thus, our findings indicate that in the early stage of a brood, the important prey may be small fish with a low body depth, whereas larger fish with greater weight may become important prey at a later stage.