Abstract

This investigation, undertaken in the two regions of Nanshi and Yujing in Tainan County over the period of 2001 to 2003, included three nests belonging to the Eastern Grass Owl (Tyto longimembris). From these, we collected a total of 157 owl pellets. Analysis and examination of the pellets revealed 329 prey items. More in-depth investigation determined that 95.1% of the Eastern Grass Owl pellets collected consisted of mammal remains, while the remaining 4.9% were made up of bird remains. Of the various types of mammals consumed, rats made up the highest proportion, with a total of 285 rats, accounting for 86.6%. This was followed by 27 shrews and moles, accounting for 8.2%. Hares and birds were seldom caught and consumed. The findings suggested that rats are the main food source of the Eastern Grass Owl, with the Spinus Country-rat (Rattus losea) comprising the majority with 136 counted (41.3%), followed by the Formosan Mouse (Mus caroli) with 96 counted (29.2%). Regarding biomass, the reversion method was used to calculate that owls at the three nests consumed approximately 22,987 grams of mammal and 480 grams of bird, accounting for 98.0% and 2.0%, respectively. The biomass consumed for each pellet was approximately 149.5 g.

中文摘要

2001 至2003 年研究期間，分別在台南縣楠西與玉井兩地，共發現三個東方草鴞 (Tyto longimembris) 的巢區，總共蒐集了157 枚食繭。食繭內容物經分析鑑定共有329 隻食餌包含其中，包括哺乳類與鳥類。東方草鴞的食繭中有95.1%是哺乳類，其餘4.9%是鳥類。哺乳類中又以囓齒目鼠類被捕捉比例較高，共有285 隻，比例86.6%。其次為食蟲目27隻，比例8.2%。兔子與鳥類被捕食的情況較少。可以看出，鼠類是東方草鴞主要食物來源，其中又以小黃腹鼠 (Rattus losea) 被捕食的比例較高，共有136 隻 (41.3%)。月鼠 (Mus caroli) 是被捕食第二多的哺乳類，共有96 隻 (29.2%)。生物量部分，利用回推方式算出此三巢東方草鴞捕食的哺乳類約有22,987 g，而鳥類有480 g，所佔的比例分別為98.0%與2.0%。每枚食繭約為消耗149.5 g 的生物量。

Keyword: Eastern Grass Owl, Tyto longimembris, pellet, diet, biomass, 東方草鴞, 食繭, 食性, 生物量