Gliding Flight in the Japanese Giant Flying Squirrel Petaurista leucogenys

抄録

Field observations of gliding and quadrupedal locomotion in the Japanese giant flying squirrel Petaurista leucogenys were made at five shrine groves with different topographies, tree densities and canopy heights. The main mode of locomotion was gliding, although arboreal quadrupedal locomotion was preferred to gliding flight in forests with a canopy height of less than 10 m, presumably because gliding was not energetically advantageous. The mean horizontal length of glides varied from 17.1-33.1 m among the study areas. Short glides of less than 10 m were infrequent. The longest glide recorded was of 115 m, but such long distance glides were rare and normally limited to circumstances where no intervening trees were available. Even when long distance glides were topographically possible, the animals tended to repeat glides of less than 50 m. Squirrels were found capable of gliding at a glide ratio (horizontal distance/vertical drop) of 3.5, but such extremes were not normal. More typically, glide ratios were found to be within the range of 1-3. Both glide ratio and speed tended to increase in longer glides, and horizontal gliding speeds ranged from 7.0-13.3 m/sec. The reasons why glides rarely approach the maximum capacity are discussed in relation to 1) wind velocity, 2) small home ranges, and 3) necessity of buffering landing impacts.