Ambush Site Selection at Night by Chinese Green Tree Vipers, Trimeresurus s. stejnegeri

• Main Authors: Fang-ru Li, 李方儒
• Other Authors: J. J. Perng
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/30402240734947443484

碩士 === 國立屏東科技大學 === 野生動物保育研究所 === 92 === Abstract We examined 1) ambush site characteristics, 2) orientations and posture of ambushing snakes and 3) the correlation between abiotic factors, preys and snakes to study the ambush site selection by the sit-and-wait pit-viper, Trimeresurus s. stejnegeri, at the stream area at night. This study was conducted from November 2001 to February 2004, at Boi-li Stream in Ping-tung County. In the 30 working nights, we observed 94 times of ambushing snakes (N=63). The proportion of female ambushing snakes observed is higher than that of male. Most of the ambush sites located at the stream section with high frog density. The shortest distance between two ambush sites was 0.5m. Almost all ambush sites located at the positions including at least one of the following three conditions：1) the distance between ambush sites and water edge (DW) < (less than) 1m, 2) the distance between ambush sites and stream bank (DS) < 1m or 3) the distance between ambush sites and the ground (DG) < 0.5m. About 51.7％（N=46） of the ambush sites located at the positions with DW < 2m, DS < 6m, and DG < 1.2m. The DS of females was longer than that of males. Almost all of the snakes ambushed either on stones or on vegetation. Only few ambush sites were on the ground. Females usually ambushed on the stones with the size: 6.5~25.5㎝, and had higher ratio using stones than males. About 72.3％（N=68）of the ambushing snakes oriented to water area. About 42.2％（N=38）of the snakes ambushed with head down toward the ground, but 53.3％（N=48）kept their heads horizontally. The forebody of ambushing snakes performed in a concertina shape, whereas the posture of the other part of body varied with different sites. When snakes ambushed on the ground, they raised their heads and kept the snout-vents horizontally. When snakes ambushed at high and flat places, their heads might hang down, put closely on the site surface or raise but keep the snout-vents horizontally. The ambushing snakes were found throughout the year during the survey period. The correlation between the number of frogs and the number of ambushing snakes sampled was not significant. The correlation between the number of ambushing snakes and abiotic factors was not significant. However, the water cover, current velocity, and water depth of the stream were negatively correlated with DW, respectively. In summary, the green tree vipers primarily searched for the stream section both with high density of preys and ambush sites available, and secondarily located at the places close by the water, above the grounds with certain height, or not far away from the stream bank. At last, the head orientation of the ambushing snakes was dependent on the movement and stay of the preys. Consequently, the results of these ambush selections would increase the probability of encountering with the preys. Particularly, in contrast to the males, the females had higher ratio for ambushing and showed a more strict selection of ambush site, indicating a higher energy requirement for females than for males.