許厝港濕地棲地改善工程對鳥類群集的影響

Abstract

濕地可提供許多生態系服務及豐富的生物資源。許厝港國家重要濕地位於桃園市，為渡冬水鳥停留北臺灣重要的濕地之一。近幾年由於溪口垃圾堆積，影響鳥類的數量與分布。因此，桃園市政府海岸管理工程處於2019年清除老街溪口的垃圾、淤泥，並移除許厝港違法的廢棄魚塭，營造為適合鳥類棲息的棲地。本研究探討棲地改善工程對棲地地景造成的改變與其對於鳥類群集的影響。地景部分以ArcGIS將工程前後的衛星影像數化進行比較，鳥類調查由2019至2021年底，每季一次。分析比較鳥類群集變化，以相似性指數分析鳥類物種組成。以10m*10m的網格和鳥類座標點位，探討鳥類於四季分布之變化。 結果顯示，工程後灘地面積大量增加。整體鳥類於工程前的量豐度低，工程中增加許多後於2020冬季後下降。種豐度部分持續上下起伏，工程中數量上升後下降，同樣於2020年秋季才又回升。棲地同功群以泥灘涉禽佔有最大比例，水域泥岸游涉禽次之，泥灘涉禽量豐度、種豐度變化與整體鳥類相似。分布在工程前後先增後減，冬季增加，夏季減少，春秋都先增後減。密度於冬、夏兩季先增後減，春季不變，秋季相反。水域泥岸游涉禽量豐度上下起伏，在工程後增加，又再下降，至2020秋季回升卻又減少。種豐度變化較小，工程前後變化不大。分布於工程前後持續上升，除冬季上升外持續下降，密度都不高，夏季下降。優勢種—東方環頸鴴、黑腹濱鷸和太平洋金斑鴴皆於工程後才出現，數量與分布先增加後減少。小白鷺數量上下起伏，分布先升後降。四季間物種相似度2020與2021年皆最接近，冬季工程前後差異較大，但夏秋兩季都以2021年差異較大。 本研究顯示鳥類量豐度雖於工程後上升，但接下來的時間幾乎都減少，而新增的棲地區域確實增加了鳥類分布的範圍。與鄰近樣區比較發現工程中、後數量上升，與其他樣區不同，但隔年的數量下降其他樣區也未出現。水質中總磷與懸浮固體與鳥類數量呈高度負相關，可能為影響鳥類數量的因子，底棲物種數量則難以解釋鳥類數量變動情形。本研究認為工程區新增的棲地確實提供鳥類可棲息的環境，但鳥類變化於隔年無法維持一定數量為主要問題。可能因工程造成之變化正好為鳥類能承受的閾值，因此工程過一年後數量急速下降。建議增加棲地水深多樣性、種植植被以增加隱蔽性，及持續監測水質，避免汙染程度過高，並注意人類與其他動物的干擾。由於調查為每季一次，易因大量單一物種的出現，造成誤差，且此研究的觀測時間較短易受影響。也可能因物種需要時間適應新的棲地，此環境是否適合鳥類持續使用仍需更長時間的監測來評估工程的成果。

The Xucuogang National Important Wetland is located in Taoyuan City, which is one of the important wetlands for winter waterfowl to rest in northern Taiwan. However, the abundance and distribution of birds seem to be affected by the trash that piled up in the estuary in recent years. Accordingly, government of Taoyuan City carried out a project to dredge Laojie estuary and to remove the abandoned illegal fish farms to create a habitat suitable for birds, in 2019. Besides, it is necessary to keep monitoring the effect of habitat management for assessment and future plans. Therefore, this study would focus on the habitat changes caused by habitat improvement projects and their impact on bird assemblages. The sample area was the Laojie estuary and the abandoned fish farm for the project in Xucuogang Wetland. For the landscape, ArcGIS was used to digitize the Google Earth satellite images. Bird surveys started from 2019 to 2021 quarterly. Furthermore, seasonal analysis of bird abundance, species number and distribution of total of birds, each guild, and dominant species were conducted. Besides, we analyzed changes in species composition by the Jaccard similarity index. Next, bird positions were overlapped on a 10m*10m grid, and the distribution of each guild of the birds was calculated. The results showed that the area of the beach had increased a lot for the change of landscape. As regards the abundance of the total of birds before the project was low but increased a lot after. However, it declined after the survey in 2020 winter. The species number increased during the project in summer, but decreased after that, and it rose again in 2020 in autumn. Regarding the guilds, mudflat waders accounted for the largest proportion, followed by water-shore waders. The trend of changing of these guilds and the species number of mudflat waders were almost the same as the total abundance of birds. The species number of water-shore waders changed slightly. As for the distribution of the guilds, the change in mudflat waders was almost the same as the abundance but did not decrease in winter after. And it was the same as the water-shore waders in winter. However, it increased slightly and then decreased a lot in autumn, and it decreased a lot in others. The dominant species of mudflat waders, Kentish Plover, Dunlin, and Pacific Golden Plover, only appeared after the project. The abundance of the above increased considerably right after the project. Conversely, they declined the next year and so as the distributions. As for mud-shore waders, Little egret, decreased except in winter. The distribution of Little egret increased in the first year and decreased then. It follows that the species similarity is the closest in 2020 and 2021 of the four seasons, and the difference is bigger in winter. This study shows that even though the abundance of birds had increased a lot right after the project, it decreased in the next year generally and so as the distribution. Anyway, the positions of birds were on the habitat which appeared after the project. In general, the changes in the abundance of birds are different to those outside the project area, it decreased a lot rather others. The total phosphorus and the suspended substrate of water quality were negative correlated to the total abundance, which may be the factor that impacted, and it is not correlated with the abundance of benthos. In conclusion, the project provided new habitat for birds. The main problem was the decrease after the next year. It may because of the change was almost at the threshold that the birds could afford. Increasing the diversity of habitat water depth, or planting vegetation for birds to hide and perch, and monitor the water quality could be the method of improving the effect. Long-term monitoring is needed to assess the project to assess the impact of the project.