以小水鴨(Anas crecca)分布探討華江濕地棲地改善工程的影響

Abstract

地處淡水河華江橋至中興橋之間的華江濕地位於新店溪及大漢溪匯流處，豐富的營養鹽以及和緩的水流營造了豐富的底棲生物相，歷年冬季吸引了大批候鳥前來度冬，其中以小水鴨(Anas crecca)數量最多。近年由於上游帶來的泥沙造成濕地淤積，產生陸域化的現象，泥灘面積的快速縮小也造成小水鴨度冬族群數量銳減，也使得濕地的經營管理顯得重要且急迫。因此台北市政府自2006年起持續每年在華江地區進行棲地改善工程。 本研究以地圖描繪法(mapping)記錄2012年9月至2013年3月以及2013年9月至2014年3月的每月鳥類調查記錄，配合遙測影像與實地調查取得之環境變數，取出泥灘面積、植被面積、水域面積、水際線長度、棲息點視野、人為活動區距離等變數進行小尺度的分析，期望了解棲地改善工程的成效、適合小水鴨棲息的環境因子以及行為和環境因子間的關係。 結果顯示在經過棲地改善工程後，2013年的小水鴨分布較2012年偏向棲地改善工程區周邊。小水鴨偏好高灘地面積、低植被面積、長水際線、視野開闊的地點棲息。相較於覓食行為，小水鴨休息時偏好離人為活動遠的地點。 雁鴨科鳥類在選擇度冬棲地時，食物資源相當重要，小水鴨等浮水鴨就經常會在水域與泥灘交界處覓食。本研究也認為為了躲避天敵以及與同伴溝通，小水鴨在選擇棲息處時也會考量視野，並且在休息時遠離人為干擾。因此建議棲地改善工程時除了現行工程營造出的大面積灘地外，也應考量延長水際線、營造低面積草澤區塊，讓小水鴨在覓食外也有躲避天敵的空間，並且區隔棲息處與人為干擾。

Huajiang Wetland is located on the merging point of Xingdian River and Da-Han River which between Hua-Jiang Bridge to Jhong-Hsing Bridge. Owing to its rich and diverse nutrients and its slow river flow, the area is endowed with a plethora of benthic invertebrates which attracts a large diversity of winter migrants, among which Eurasian Teal (Anas crecca) occupying the majority. In recent years, the accumulation of sediments from upper stream has caused an increase in terrestrialization on the cost of mud flat areas with a sharp decrease on the number of wintering Eurasian Teal. It is now apparent that the management of these wetlands is of utmost importance. Therefore, the Taipei City Government continued annually habitat improvement plan in Huajiang area since 2006. Present study utilizes monthly bird monitoring by mapping method from Sept, 2012 to March 2013 and Sept 2013 to March 2014. In addition to remote sensing data, actual survey data was utilized to obtain environmental data. Data analysis was conducted to variables including area of mud flat, area of vegetation cover, area of water, length of mud-water interface, visual field of ducks, and distance of Eurasian Teal from human disturbances. We look forward to better understand the efficiency of habitat improvement plan, environmental variables preferred by Eurasian Teal, and relation between duck behavior and environmental variables. The result shows that ducks preferred post recovery area, after the habitat improvement plan was carried out. Eurasian Teal prefer to roost at sites with vast mud flat area, narrow vegetation area, long shore lines, and broad vision. Comparing with feeding time, Eurasian Teal prefer sites away from human disturbance in resting time. Food resource is very important for wintering waterfowl choosing habitat. Dabbling ducks such as Eurasian Teal usually feeding at mud-water interface. To avoid predators and communicate with other ducks, Eurasian Teal will choose a habitat which has better visual field. Eurasian Teal will stay away from human disturbance. Except vast mud flat area constructed by current habitat improvement plan, we suggest that extending shore lines and constructing narrow marsh area should be take into consideration in the future. So that Eurasian Teal can feed and avoid predators at the same time, also separate resting site from human disturbance.