中文摘要
在造橋地區進行的赤尾青竹絲Trimeresurus stejnegeri長期研究中，明顯呈現較多雄蛇出現的現象。因此，我懷疑這樣的情形，可能是因為在生殖過程中，有較多的雄性個體誕生；兩性個體在活動模式、棲地選擇利用的差異，造成我們的取樣誤差；或是出生後雌性個體的高死亡率、高遷出率，導致族群內雌蛇數量的減少，因而得到性別比偏離 1的觀察結果。
於是，每月至少一晚，我沿樣區內固定穿越線進行夜間採樣記錄工作。在三年裡，於各季出現的雄蛇個體數顯然多於雌蛇，且達到顯著水準(t=-4.99, P＜0.001)，顯示雌蛇並無規則性的於特定季節出現個體數量多過雄蛇；而兩性個體在清晨、正午、傍晚三個不同時段的出現情形，在為期一年的每月觀察中，無論在任何時段中，都以雄性個體的數量較多。但是，只有傍晚的兩性個體出現比例，到達顯著水準 (χ2=4.98; df=1; P＜0.05)；而在赤尾青竹絲的活動上，雌蛇也不比雄性強，因此不會有較高的雌蛇遷出率。
兩性個體的微棲地利用並無不同；且無論樹林內部(χ2=8.16, df=1, P＜0.01)，還是樹林邊緣的利用情形(χ2=31.14, df=1, P＜0.001)，都顯著的以雄蛇為多。同時，在造橋地區並未發現有區域性雌蛇數量較多的現象，顯示赤尾青竹絲性別比偏離 1的現象並非僅發生於研究樣區內部。
於兩個生殖季中，共在造橋地區得到17隻懷孕雌蛇，產下45隻雄性仔蛇、32隻雌性仔蛇。結果顯示，造橋地區赤尾青竹絲族群的初生性別比並未偏離 1(χ2=2.2, df=1, P＞0.05)。因為兩性個體在活動性及棲地利用上，不會造成研究的取樣誤差，而實際標放個體資料中，樣區內赤尾青竹絲之族群整體性別比，也顯著偏離 1 (χ2=31.94, df=1, P＜0.001)。因此，雌性赤尾青竹絲因生殖而導致的高死亡率，應是造成赤尾青竹絲族群性別比偏離 1的主因。
我將所有標放個體，以誕生幼蛇平均體長為依據，每間隔10cm分為一個成長群，共分為一至四群。所得結果經分析後，僅第四群有顯著偏離1的現象(χ2=33.38, df=1, P＜0.001)，其餘三組均未達顯著水準。再將初生性別比一起併入，五組性別比數據相鄰兩組間進行比較。結果初生性別比與第一群、第一群與第二群、第二群與第三群間，性別比均無明顯不同，只有第三群與第四群間有顯著差異(χ2=12.14, df=1, P＜0.001)。顯示當成長階段進入第四群後，也就是完全達到性成熟後，性別比偏離 1的現象才逐漸浮現。

英文摘要
A male-biased sampling of Chinese green tree viper, Trimeresurus s. stejnegeri, was found at Tsao-chiao study site. Animal skewed sex ratio may induced by various reasons. Although unlikely, the skewed sex ratio at birth was still found in a few snake species. Sampling bias and/or differential mortality rate between sexes are more likely to be the causes of the observed skewed sex ratio. The aim of this study is to find out the cause of this skewed sex ratio.
By marking each individual, which encountered in the study site for 3 years, I could identify a total of 169 males and 79 females. The overall population sex ratio is significantly biased toward males(χ2=31.94, df=1, P＜0.001). I checked whether females may become more abundant than males at certain seasons or time of a day. But the results didn't support such speculation. If habitat preference is different between sexes, it may bias toward males by sampling at only one type of habitat. Other than the main transect located at the edge of the deciduous forest, I surveyed another transect in the forest for one year. Both transects had significantly more males than females. Besides, I checked the vicinities of the study site occasionally and found the same male-biased sex ratio.
17 gravid females were collected from Tsao-chiao area in 2 consecutive reproductive seasons. A total of 77 newborn snakes(45 males and 32 females) were obtained in the laboratory. At birth, though the males are slightly more than females, there was no significant biased sex ratio(χ2=2.2, df=1, P＞0.05).
Clearly, neither sampling bias nor differential birth rate between sexes was responsible for the skewed sex ratio of T. s. stejnegeri in Tsao-chiao. A differential mortality between sexes is likely to be the cause of this skewed sex ratio. I further divided the marked individuals into 4 groups according to their Snout-vent length. It revealed only the last group, which included all the mature individuals was significantly biased toward male. This implies mature females seem to have higher mortality rate than males.

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