九州

The changes in population size and home range of the Japanese field vole, Microtus montebelli, were investigated on two grids set near the summit of Mt. Hitome situating on the border between Kumamoto and Oita Prefecture from December 1975 to December 1980. One grid (GKA) was located on a young plantation of Hinoki cypress (Chamaecyparis obtusa) on the west side and another (GKB) on a native grassland on the east side of a ridge. One more grid (GAA) was established on a native grassland on the top of the northern somma of Aso from September 1977 to November 1980. The area of each grid was 0.49 hectare (70m×70m) and the total of 196 traps (14×14) were set with five meters' trap spacing. The mark-and-recapture method with live-traps was applied to the grid GKA for three days and the removal method with snap-traps to the grid GKB for three days, while the removal method was used on the grid GAA for monly a night. Investigations were carried out 27 times on the grid GKA, 17 times on the grid GKB and 15 times on the grid GAA. The results obtained are summarized as follows: 1. On the grid GKA, a remarkable population growth in June 1976 appeared to have begun in spring of 1975, and after that the population size indicated a declining tendency up to December 1980. Onthe grid GKB, the voles had been poisoned with the rodenticide Z·P (Zn2P3) in late November 1975 just begore the first investigation, and the control effects were evaluated to have lasted for about a year. 2. On the grid GKA, the population density at the first time of investigation was 62.8/ha, when a large number of the young Hinoki cypress, eulalia (Miscanthus sinensis), bamboo grasses (Sasa nipponica and Arundinaria pygmaea) and other plants had been damaged by the voles in the study area at Mt. Hitome. The highest density (145.1/ha) was recorded in June 1976, and the damage continued under the density of 62.7/ha up to August of the same year. The vegetation showed signs of recovery in 1978. 3. On the grid GAA where the prescribed burning in spring and grass cutting in fall have beenn gractised very year, the population has been stabilized with a low density compared with population density on the grid GKA. The factor accountable for the low density seemed to involve the loss of shelter and temporary shortage of food which suppress the vole's outbreak. 4. On the grid GKA, there was no sex defference in the home range for adults under high density, but the male home range became remarkably longerthan female one under the low density, although it fluctuated more than did the females' range; thus the difference in density was strongly influential for males. It was interesting that there appeared frequently males with a placid temper under the high density. On the other hand, in subadults the size of home range hardly had any connection with the density, although they had great individual variations.