札幌市円山動物園におけるチンパンジーのタワーへの昇降行動の変化

抄録

 Nowadays, zoos are expected to provide facilities that place importance on the living environment of the animals, which should belong in their natural habitats. In a wild rainforest where chimpanzee's live, understories surround tall trees exceeding 20m in height. Chimpanzees, which are semi-arboreal animals, use them when transferring themselves between the treetop and the ground. At the outdoor chimpanzee facility in the Sapporo Maruyama Zoo, ropes, logs, imitation trees were additionally installed as understory substitutes around the tower, that was introduced for environmental enrichment. The objective of this research is to measure the changes in the behavior of the chimpanzees going up and down the tower caused by the additional elements, reveal its causes, and determine what spatial elements around the base of the tower are effective in guiding the animals up the tower.
 We conducted a behavioral study focusing on the elements used by the chimpanzees during arboreal locomotion on the tower at Sapporo Maruyama Zoo. We separated the tower from its form and its materials into its components, and measured how frequently the tower elements had been used, position of going up and down the tower and trigger elements according to their age.
 As a result, it was discovered that the imitation tree side platforms, logs and gently inclined ropes that were additionally installed around the tower, were highly influential as they were used by the chimpanzees as an opportunity to move up and down the tower. In particular, by placing a side platform on the left side of the base of the tower, it made it easier to go up and down the tower, increased going up and down the tower from the left, and increased the number of movements by the adults. The logs with gentle inclinations subtending less than 40° with the ground were mainly used for the ascents. Also, the ropes inclined at approximately 25° allowed the intersecting ropes to be used in combination and the usage of the ropes as a whole was increased. Direct climbing of the column ceased, as other handholds were now available in the surrounding area. Moreover, the two ropes connecting the exit from the room to the tower were frequently used as a means of aerial movement instead of using the ground. For the Adult group, there was no change in the basic behavior of climbing the tower by using mainly the columns and the composite materials (beams, piers and decks). However, they began to use the side platforms and logs en route to the column. Also, the object they grasped for support in the beginning changed from the thick pipes to the horizontal ropes. In contrast, the Young group showed a major change in the element usage itself, where they used to descend to the ground via the columns, but now they have changed to jumping off the horizontal ropes using its momentum.
 From the above, the following four spatial elements around the base of the tower were found to be effective in guiding the animals up the tower:
 1. Placing a solid footing by the base of the tower. It should be positioned such that the distance between the footing and the objects on the tower that can be grasped is less than the height of the chimpanzee.
 2. Install a slip-resistant diagonal members inclined at less than 40° to the ground with handholds, such as logs with bark.
 3. Place ropes arranged so that they intersect with each other. The inclination of the horizontal ropes should be no more than 25°.
 4. Install an aerial path to the tower without coming down to the ground.