探討度冬大杓鷸族群在彰化灘地之分布

Abstract

度冬水鳥利用潮間帶灘地覓食補充能量，水鳥在灘地上的分布和灘地類型有關。在過去三十年，台灣度冬大杓鷸（Numenius arquata）在彰化灘地歷經分布改變和數量減少。分布改變代表適合棲息的環境改變，欲了解分布改變之因，需先了解大杓鷸分布於何種灘地類型。觀察大杓鷸在彰化海岸的分布，以及分布範圍內的底質類型，發現大杓鷸分布主要分布在芳苑外海灘地，分布範圍內地底質為泥質，在灘地上的主要行為為休息和覓食。為探討彰化海岸底質分布，利用大地衛星影像進行監督式分類和138個現場灘地的底質資訊，將彰化灘地底質分為沙質和泥質，結果顯示衛星影像分類之整體精確度為94%。由影像分類結果發現彰化海岸許多地方是泥質底質，但大杓鷸分布僅在芳苑外海灘地，顯示有其他因子影響大杓鷸在泥質灘地的分布。檢測漲潮停棲點和人為干擾是否對大杓鷸在泥質灘地分布有影響，比較有大杓鷸分布之泥質底質與無大杓鷸分布者，距漲潮停棲點、風力發電機、蚵架、台61西濱高架快速道路之最近距離有無差異。結果顯示有大杓鷸分布的泥質區域距漲潮停棲點較近，且距風力發電機、台61西濱高架快速道路較遠。本研究顯示彰化度冬大杓鷸族群偏好泥質灘地，且其分布之泥質區域距離漲潮停棲點近、距高架道路較遠。過去三十年，風力發電機、台61西濱高架道路尚未建立，欲探討分布改變，可以泥質灘地變遷、漲潮停棲點位置的變化來探討。欲保育彰化海岸大杓鷸的棲地，除了保育灘地底質之外，需將漲潮停棲點的位置和高架道路的干擾納入考慮。

Mudflat is the primary foraging habitat of wintering shorebirds. Shorebird distribution is related to mudflat type. The wintering population of Eurasian Curlew（Numenius arquata）shifted its distribution in the past 30 years in Chang-hua coastline. Curlew distribution change represents changes in their optimal habitat. In order to understand the cause of the distribution change, we must understand the preferred mudflat types for curlews. To do so, we observed wintering curlews’ distribution range on intertidal mudflat in Chang-hua coastline and studied the mudflat types in their distribution range. We found curlews mainly distribute themselves in Fang-yuan mudflat; furthermore, they seemed to prefer muddy substrates. Whilst there, their major behaviors included resting and feeding. To understand the substrate distribution of Chang-hua region, we collected 138 samples in the field and used Landsat satellite imagery to classify the mudflat type to ‘sand’ and’ mud’ through supervised classification. The overall accuracy of the classified map is 94%. Form the classified theme map, it was apparent that there were many muddy areas in Chang-hua coastline, but curlews, however, distributed themselves in particular muddy region of Fang-yuan. This suggested that there are others factors that affect curlews’ distribution on ’ muddy’ mudflats. We test whether if the distance to high tide roosting sites and human disturbances affect curlews’ distribution on ’muddy’ mudflat. Comparing between the ‘muddy’ mudflat areas with curlews and those without, we tested whether if the distances to (1) high tide roosting site and (2) wind turbines, (3) oyster culturing structure and (4) No. 61 West Coast Expressway were the factors in terms of curlew distribution. Our result revealed that curlews were distributed in ‘muddy’ regions near high tide roosting site. They were, on the other hand, distributed further away from wind turbines and No. 61 West Coast Expressway. 30 years earlier, none of the aforementioned infrastructures constructed. In hope to better understand curlews’ distribution change over the past 30 years, future studies must investigate (1) the change of ‘muddy’ mudflats and (2) the change in high tide roosting sites in north Chang-hua. Present study highlights the importance of mudflats on curlew conservation. While placing emphasis on the distance to feeding and roosting sites, it has come to light that various types of human disturbances may also play an important role in the distribution preference of the Eurasian Curlew.