臺灣八色鳥分布特性

Abstract

八色鳥(Pitta nympha)為東亞遷徙性鳥種，全球性的易危鳥種之一，在臺灣屬夏候鳥，是其物種重要繁殖地之一，近年研究指出在臺繁殖八色鳥之族群數量持續下降，且北部下降最為明顯。本研究試從過去2001年至2017年點位資料中瞭解八色鳥分布狀況，整理了三十個環境因子探討物種棲地偏好環境，利用分布預測模式來瞭解影響八色鳥在臺分布的環境因子各貢獻度為何，以及推估目前臺灣八色鳥分布範圍，另外針對重點調查地點如：石門水庫、苗栗獅潭大湖、曾文水庫、美濃山區以及湖山水庫，進行年間大地衛星影像之分析棲地時空變化，比照經由監測資料趨勢與指數算出之年間族群指數，來查看巨觀棲地之變化對於八色鳥族群數量是否有影響。結果認為分布和過去研究所做之分布預測模型大致吻合，可得知八色鳥在臺環境偏好變化不大，影響出現之環境因子重要度以闊葉林面積最為重要，呈現正相關，其餘海拔標準差、農田地面積、海拔高度、竹林地面積等因子貢獻度較高，皆為棲地特徵類型因子，而主要調查地區族群數量上湖山水庫、石門水庫、美濃山區數量呈現下降趨勢，曾文水庫在數量呈現上升趨勢，衛星影像判別之地景分析上，除了湖山水庫有較大棲地上變化，其餘植物面積皆無明顯減少或上升。對於候鳥的研究，要考慮繁殖地與各度冬地兩地的棲地情況，近年八色鳥主要度冬地之一的婆羅洲因油棕樹的種植，取代了部分棲息環境，度冬存活率如果下降，對繁殖地的數目也會有衝擊，過去研究認為八色鳥在台灣各分區間數量下降速度不同，推測臺灣本島有來自不同度冬地的八色鳥族群並未遭受到棲地上的破壞。臺灣為八色鳥重要繁殖地，對保育存在不可或缺的角色，本研究試圖找出八色鳥偏好的環境因子，認為棲地特徵上的影響比氣候、人為活動等更為首要考量，希冀此研究可給予國際間八色鳥物種保育時更明確的方向。

Fairy Pitta (Pitta nympha) is a migratory bird species in East Asia. It is a summer migrant in Taiwan and one of the most vulnerable species in the world. In recent years, the number of Fairy Pitta in Taiwan has decreased, and a significant decline has been observed in the northern area of Taiwan. This study uses 30 environmental factors to explore the habitat preferences of Fairy Pitta and ranking the contribution of each environmental factors by using the species distribution model, and then estimated the current distribution of pitta nympha in Taiwan. In addition, this study uses satellite imagery to evaluate the temporal and spatial changes of the main survey sites such as: Shimen Reservoir, Miaoli, Zengwen Reservoir, Meinong and Hushan Reservoir. The results show that the distribution range is agree with previous studies, and it can be seen that the pitta nympha has little change in the environmental preference in Taiwan. The most importance environmental factors is the broad-leaved forest area, with a positive correlation. Other factors are the standard deviation of altitude, farmland area, altitude, and bamboo forest area. A decreasing trend was observed in number of Fairy Pitta in Hushan Reservoir, Shimen Reservoir, and Meinong while an increasing trend showed in Zengwen Reservoir. In the other hand, the forest areas have not decreased or increased significantly in satellite image of habitat except for the Hushan Reservoir. For the study of migratory birds, the habitats of the breeding grounds and the wintering sites should be considered as well. Main wintering sites: Borneo, where the natural forest area has been greatly reduced due to the cultivation of oil palm trees in recent years. In Taiwan, the number of Fairy Pitta in each region has declined with different rates. Therefore, we hypothesize that Fairy Pitta may come from different wintering sites. Taiwan is an important breeding ground and plays an important role in international conservation. This study provides the direction of species conservation in Fairy Pitta and demonstrates that the impact of habitat characteristics is more important than climate, human activities, etc.