生態及社會因子對冠羽畫眉（Yuhina brunneiceps）偶外配對的影響

Abstract

Extrapair copulation（EPC） is a common behaviour in monogamous species, the current researches usually infer that EPC is for gaining indirect benefit like improving offspring genetic quality, but lack of discussion about influences from other factors. Taiwan Yuhinas （Yuhina brunneiceps） cooperate with unrelated individuals for joint-nesting, they have more chances to meet potential extrapair mate：27.55% of Taiwan Yuhina offspring are extrapair offspring（EPO）, and 58% of EPO are born with individuals in same breeding group. This research analyses the influence to the probability of EPO from ecological factors and social factors, data is from breeding season in 2001, 2003-2007. Analysis by ecological factors include precipitation and temperature, social factors include group size, hierarchy, relatedness. The result shows subordinate females tend to have more EPO with fewer precipitation, but among different hierarchicval females there’s no significant of having EPO while with more precipitation. Another result shows if a female has a more related social mate, there is more probability to seek intergroup EPC with more unrelated individuals outside the groups, and the intergroup EPO have more probability to be male. These results indicate that EPC affected by social factors and ecological factors simutaneously, and lower hierarchical females tend to seek EPC when the environmental condition is better, so ecological factors play important roles on parents-gaining-direct benefits, seeking EPC shall find a balance between the benefit for offspring and cost of parents.