Abstract
Life history studies of the Japanese Rock Ptarmigan Lagopus muta japonica provide important information on this subspecies' adaptation to cold environments and the effects of global warming on it. In this study, we examined the breeding and wintering ecology, seasonal flock composition, and altitudinal movements of the Japanese Rock Ptarmigan on Mt Norikura. In relation to seasonal changes in the weather conditions of the alpine zone, the size and composition of ptarmigan flocks varied five times within a year reflecting stages of the life cycle: movement to the breeding area, commencement of incubation, the hatching period, the beginning of independence from parental care, and movement to the wintering. All birds left the alpine zone in winter, but gender segregation of wintering areas occurred. Males observed in a wintering area had bred in areas nearby. However, the area in which females wintered (as revealed by radio tracking), was steeper and at lower elevations than males. Realized sex ratios were skewed towards males throughout the year, but observed sex ratios varied in relation to changes in ptarmigan life history. Taken together, our findings revealed that in comparison with foreign populations and related species the Japanese Rock Ptarmigan exhibits complete separation of breeding and wintering areas but lacks summer movements to higher elevations as reported in other subspecies or related species of other countries. We suggest that these characteristics of the Japanese Rock Ptarmigan may be in response to heavy snow in winter and to the distribution of alpine vegetation in the alpine zone. Finally, we suggest that among alpine ptarmigans the subspecies of the Rock Ptarmigan in Japan is the most sensitive to global warming.
