蘭嶼角鴞（Otus elegans botelensis）的巢洞選擇

Abstract

蘭嶼角鴞（Otus elegans botelensis）為Otus elegans的蘭嶼亞種，僅分佈於蘭嶼地區，目前族群數量剩下約1000隻。蘭嶼角鴞是不會自行鑿洞的樹洞營巢性鳥類（secondary cavity-nesting birds），其繁殖成功與否受到巢洞可獲得性及品質的影響。本研究探討蘭嶼角鴞選擇巢洞時的偏好與依據的因數，以及哪些巢洞因數與角鴞繁殖成功與否有關。研究人員於2000年繁殖季，選擇蘭嶼森林中角鴞繁殖密度較高的地點作為樣區，進行樹與樹洞普查，測量項目包括巢樹特徵值、樹洞形值、洞內微氣候狀況以及洞內狀態資料，此外並配合繁殖記錄將樹洞區分為「巢洞」與「未被使用的樹洞」以探討角鴞的巢洞選擇，再將巢洞區分為「繁殖成功」與「繁殖失敗」者以瞭解角鴞繁殖成功與否與巢洞形值的相關性。研究結果顯示，蘭嶼角鴞使用巢洞時具有選擇性，並非隨機利用樹洞；選擇巢洞時主要的依據是樹洞的洞內大小、洞內潮濕程度、樹洞底部傾斜程度、樹洞底部平坦程度、以及樹洞離地面高度。而與角鴞繁殖成功與否相關的因數包括樹洞離地面高度、洞內寬、洞內體積、以及洞內潮濕程度。對蘭嶼角鴞而言，「合適的巢洞」應是離地面較高、洞內乾燥平緩且體積較大的樹洞，這樣的巢洞應能提供較安全與適合撫育下一代的環境。

Lanyu scops owl (Otus elegans botelensis), a subspecies of Otus elegans, inhabits in Island Lanyu only. Their population size is around 1000. Lanyu scops owl is one kind of secondary cavity-nesting birds, they cannot excavate a hole by themselves. Their success of breeding depends on availability and quantity of cavities. In the current study, possible bases of cavity selection are investigated. In the breeding season in 2000, a region with high density of breeding pairs was chosen as the experimental area. Elements of trees and cavities were measured, including characteristics of a tree, characteristics of a cavity, and micro-climate in a cavity. The results suggest that Lanyu scops owl selects specific cavities as their nests. Size of a cavity, moisture in a cavity, gradient of surface in a cavity, smooth of surface in a cavity, and height of a cavity could lead a cavity to be selected or not. For Lanyu scops owl, a high, large, dry, and smooth cavity is a good candidate. Such a cavity could provide a safe and comfortable environment.