1982 年 14 巻 2-3 号 p. 232-245
Located at about 30km north-west of Akita City, a colony of the Grey Heron (Ardea cinerea) has been maintained at the foot of Mt. Honzan in Oga Peninsula. It is surrounded by a natural 24.8ha cedar (Criptomeria japonica) forest of about 215 trees, approximately 150 years old. We made a distribution map of cedar trees and marked every tree, and their nest sites were indicated. The population size of Grey Herons in this colony was estimated to be about 390 in 1980 and 400 in 1981. All-day observations were done to investigate their feeding behavior. Departure and return to and from the colony were frequent both in the morning and the evening. The dropped foods, dead-nestlings and adult birds were eaten by mice and unknown middle-sized mammals, and decomposed by many insects. The Grey Heron colony has existed very long time, and big old cedar trees are gradually dying year by year. As the result, the whole colony is forced to move toward the north of the forest.