黑面琵鷺度冬棲地的偏好

Abstract

1990年，黑面琵鷺被列為「極度瀕危(CR, Critically Endangered)」的物種，然而隨著保育觀念的提升，及全球同步普查的努力，黑面琵鷺的全球數量才開始有上升的趨勢；但即使數量有所成長，現今在東亞各地區仍舊面臨著棲地的喪失、食源的減少等威脅。 從香港觀鳥會發行的「黑臉琵鷺全球同步普查 2017」報告書中，篩選出大於該年度黑面琵鷺調查總數1%的地區做為度冬熱點；並在這最終的11個樣區中，利用衛星影像進行棲地類型判定與面積統計，得到樣區範圍內的棲地組成與分布狀況。藉著分析2017年黑面琵鷺的度冬熱點，來瞭解牠們對度冬地的選擇與偏好。 從歷年度冬地的地理位置分析中，推測黑面琵鷺偏好在東亞緯度34.0°N 到19.0°N 之間的範圍度冬，而度冬族群的分布主要是受棲地品質的影響。黑面琵鷺白天群聚休息的群棲地，多有完整面積的灘地且干擾低；並無特別偏好的群棲地類型，11個熱點中鹽田、林沼澤／紅樹林及河口三角洲皆是樣區中心的主要群棲地類型。覓食棲地共有漁塭、河口三角洲及潟湖三種棲地類型，得到從群棲地中心移動距離5公里的範圍內，覓食棲地總面積與黑面琵鷺隻數有顯著高解釋力；而覓食棲地對黑面琵鷺族群的影響力大於群棲地，故各熱點應優先針對覓食棲地進行評估及保護。另外，11個熱點中共有10個樣區範圍內有設立針對濕地的保護區，其中達到有效管理的共9個熱點，確實有發揮保育黑面琵鷺的功能。 一旦棲地承載量無法負荷或是遭破壞，就可能導致黑面琵鷺尋找更外圍的可用覓食棲地，甚至移棲到其他地區度冬，形成在熱點主棲地周圍的衛星棲地。在族群成長逐漸趨緩的現今，可以藉著研究成果的熱點特色找尋現存熱點附近的潛在熱點，並進行棲地維護；以增加黑面琵鷺的可用棲地，同時減少風險。

In 1990, Black-faced Spoonbill (Platalea minor) was listed as Critically Endangered. Since then, with the improvement of public awareness and the efforts of the international census, the number of Black-faced spoonbill has been recovering increased. However, even if the population has grown, the wintering sites from the coastal area on the eastern fringe of Asia are still facing threats, such as loss of wintering habitat and reduction of food resources. The regions recorded more than 1% of the total number in 2017 are selected as wintering hot spots, from the 'The International Black-faced Spoonbill Census 2017' report, issued by the Hong Kong Bird Watching Society. For the final 11 sample areas, Landsat satellite imagery was used to determine habitat type and calculate their area. Furthermore, this study is to obtain the composition and distribution of habitats within the sample areas. By analyzing the wintering hot spots of the Black-faced spoonbill in 2017, we can verify their choices and preferences for wintering sites. From the geographical analysis of the wintering sites in the past years, the results implied that the Black-faced spoonbill prefers wintering in the region of latitude 34.0 ° N to 19.0 ° N in East Asia, and the distribution of wintering population is mainly affected by the quality of habitats. During daytime, the wetlands where Black-faced spoonbill are used to gathering and resting in, are defined as “roosting habitats”, mostly with a large area and low interference. It shows that there is no particular preference for the type of roosting habitats, which salt pans, mangroves, and estuary are the main types in the center among the selected hot spots. There are three types of “foraging habitats” with rich food resource, such as fish ponds, estuary, and lagoon. Within a range of 5 kilometers from the center of the hot spot, the total area of foraging habitat had a high predictive power on the number of Black-faced spoonbill. Foraging habitats have a greater influence on the Black-faced spoonbill than the roosting habitats, so it is recommended that the authority should give priority to the evaluation and protection of foraging habitats in their hot spot area. In addition, 10 sample areas out of 11 hot spots have established protected areas for wetlands, and among all selected hot spots, only 9 of those that have been properly managed, actually carry out the function of conserving Black-faced spoonbill. Once the habitat exceeds the carrying capacity or gets worse, it may cause the Black-faced spoonbill to search for more available foraging habitats in the outer periphery, or even migrate to other areas to spend the winter, forming satellite habitats around the main hot spots. Nowadays, while the growth of population gradually slowing down, we can use the characteristics of hot spot, discovered from research results, to find potential hot spots near existing ones and to carry out habitat maintenance; by increasing the number of available habitat, can we reduce risks of the Black-faced spoonbill.