ニホンザルにおけるGPS首輪による測位の成否と誤差に影響する要因

抄録

We tested the success rate and accuracy of GPS collar positioning for a free-ranging Japanese macaque. The orientation of the GPS unit, behavior of subject monkey and environmental conditions during positioning attempts were videotaped, in order to examine the factors affecting success rate and accuracy. Total positioning success rate was 38 % (54 success in 142 trials). Orientation of the collar GPS unit primarily influenced the positioning success rate. Success rate was 81 % when the collar GPS unit was oriented above or horizontal to the gravity, while all positioning attemps failed when the collar GPS unit was oriented downward. Vegetation also affected the success rate. Success rate was lower in the evergreen broad-leaved forest than those in the feeding site, grassland and defoliated broad-leaved forest. Orientation of the GPS unit was not seriously affected by positional behavior of the monkey. Frequent manipulation of the GPS collar by the subject monkey caused the changes in the relative position of the GPS unit around the neck (dorsal, ventral or side). On the other hand, other monkeys did not touch the collar. We conducted positioning by handheld GPS (Garmin GPS V) at the same time and place of each GPS collar positioning attempt. The difference between coordinate values of the GPS collar and that of the handheld GPS was 13.2 m on average, suggesting that the accuracy of the GPS collar is comparable to that of a handheld GPS. Effect of vegetation on the difference between coordinates recorded by the GPS collar and by the handheld GPS was not detected. The results clearly indicate that the orientation of the GPS unit is of primary importance to achieve higher success rate in GPS telemetry. In applying GPS telemetry to primate research, measures to stabilize the GPS orientation to upwards, no matter how hard the animal manipulates the GPS collar, must be considered.