冠羽畫眉巢位選擇和親鳥活動交互作用對巢被捕食之影響

Abstract

避免巢被捕食的策略演化被認為與親鳥的行為與巢位選擇有關。親鳥的存在對於沒有能力防禦自己巢的物種，會增加巢被捕食的危機；而巢的隱密度則可以提高其繁殖成功率。親鳥行為與巢位選擇對捕食率各自的影響已被研究多時，用以解釋避免巢被捕食的策略。研究發現親鳥行為的影響與巢位的影響有交互作用。但這些交互作用的詳細機制尚未明瞭。本研究的目標在於瞭解親鳥活動與巢位選擇兩因子是否對於巢捕食率有交互作用及其詳細機制。我們利用兩個操作實驗以及一個觀察測量實驗相互比較來瞭解兩個因子分別的影響及交互作用關係。研究結果顯示巢位選擇對巢捕食率有正面影響而親鳥活動與巢捕食率則有負面的關係。這兩個因子在自然巢的時候互相抵銷而觀察到對巢成功率中性沒有影響的結果，但在假巢中卻完全沒有影響。這研究顯示兩個結論：(1)親鳥活動因子和巢位因子對巢捕食率同時有相互彌補的作用與交互作用產生。(2)將假巢的結果外推到真實族群狀況可能會造成結果偏差，需要在有親鳥的狀況下利用明確而清楚的操作實驗來檢測兩因子分別的影響。

The evolution of nest predation avoidance tactics is thought to associate with parental behavior and nest site selection. Parental existence can increase the risk of nest predation for the species who has limited ability of defense, but concealed nest site could raise the nest survival rates. The effects of parental behavior and nest site selection have been demonstrated to interact with each other. The aims of our experiments were to determine if there were interactions between two factors influencing the rates of predation and investigate the underlying mechanisms of these interacted effects. We addressed two manipulating experiments to determine the net effect separately in active nests. The net effect of nest site on nest predation was examined by manipulating the level of foliage cover. The net effect of parental behavior was investigated by comparing the survival rates of active and inactive nests. Results indicated nest concealment revealed positive relationship and parental active activity showed negative concern on nest predation. These two factors compensated each other and showed a neutral effect on nest predation in active nests but did not show the significant importance in inactive nests. This study demonstrated two conclusions: (1) interactions and compensations between parental activity and nest site effect are existed influencing nest predation. (2)Extrapolation the result from inactive nest to real population may cause potential bias and a clear-cut manipulating experiment to examine the separating effect in active nests was recommended.