2011 年 60 巻 2 号 p. 200-215
Lagopus mutus japonicus is the southernmost subspecies of Rock Ptarmigan. This susbspecies is a relic population, remaining after the most recent ice age, isolated on mountain peaks and ridges of central Honshu, Japan, where it inhabits the alpine zone. Seasonal changes in food items were investigated by observations of ptarmigan foraging behavior on Mt. Norikura. Among the total 46,523 pecks observed throughout a year, 92.9% of them were made at vegetable matter, 4.7% at animal matter and the remaining 2.4% were made at inorganic matter such as grit. Rock Ptarmigan in Japan winter in the subalpine area below 2,600 m where their main winter food consists of the buds of Betula ermanii extending above the snow. After returning to the alpine zone in April, their main diet changed for the leaves of evergreen-dwarf-shrubs including Empetrum nigrum, Vaccinium vitis-idaea, and Arcterica nana. During May and early June they were also observed feeding on small insects, Aeolian plankton, deposited on the snow surface by updrafts from the lowlands. In addition to the leaves of evergreen-dwarf-shrubs, the flowers of deciduous-dwarf-shrubs and herbaceous plants were their main foods in summer. Many kinds of fruits and seeds are eaten in autumn. It was found that the diet of ptarmigan in Honshu, changed considerably both in quantity and in quality with seasonal changes in snow conditions and plant growth. The close relationship between the seasonal diet and the life history of the ptarmigan in the alpine environment was discussed.