鷸鴴類岸鳥在魚塭環境的群棲地選擇與偏好

Abstract

鷸鴴類岸鳥度冬或過境棲地可分為覓食棲地與群棲地，後者指滿潮時岸鳥從潮間帶飛至內陸成群休息之棲地，兩者缺一不可。台灣彰化海岸屬東亞澳遷徙線上一重要度冬地與過境地，養殖區的魚塭堤岸成為岸鳥主要的滿潮群棲地。過去在自然環境進行的研究指出掠食風險與能量限制是影響岸鳥群棲地選擇的主要因素，但極少有針對魚塭環境的研究。魚塭環境和自然環境的差異可能影響岸鳥在此環境的群棲地選擇。本研究的目的包括（1）確認岸鳥在魚塭環境的群棲地利用具選擇性，並比較不同岸鳥的群棲環境偏好差異。（2）比較各環境變數之相對重要性，以瞭解岸鳥在魚塭環境的群棲地選擇主要受何種因素影響。 2011年10月至2012年5月在彰化濱海養殖區進行鳥類調查，並利用實地測量與遙測影像取得6種環境變數，包括堤長、植覆等級、天空能見度、覓食地距離、底質種類及可否避風。利用群集分析將樣本數較小的物種依使用堤岸的相似度分群後，用單變數分析比較使用堤岸和整體堤岸的環境變數差異，確認岸鳥在魚塭環境的群棲地利用具選擇性，並比較不同物種間的偏好差異。最後用廣義線性模式及模式平均法，比較各環境變數之相對重要性。 研究期間共記錄到鷸鴴類岸鳥18種，共使用147條魚塭堤作為群棲點，東方環頸鴴（Charadrius alexandrinus）數量和使用堤數最高，其次為黑腹濱鷸（Calidris alpina）。群集分析將東方環頸鴴和黑腹濱鷸以外的16種岸鳥分成兩群，類群1包括太平洋金斑鴴（Pluvialis fulva）、青足鷸（Tringa nebularia）、小青足鷸（Tringa stagnatilis）及赤足鷸（Tringa totanus），類群2包括灰斑鴴（Pluvialis squatarola）、反嘴鷸（Xenus cinereus）、大杓鷸（Numenius arquata）、大濱鷸（Calidris tenuirostris）、鐵嘴鴴（Charadrius leschenaultii）、蒙古鴴（Charadrius mongolus）、翻石鷸（Arenaria interpres）、紅胸濱鷸（Calidris ruficollis）、三趾濱鷸（Calidris alba）、紅腹濱鷸（Calidris canutus）、彎嘴濱鷸（Calidris ferruginea）及黃足鷸（Tringa brevipes）。單變數分析結果顯示所有物種與類群的岸鳥會選擇長度較長、距覓食地較近、能避風且天空能見度較高的堤岸群棲。類群1多數利用植覆較多的土堤，其他岸鳥則偏好植覆較少的水泥堤群棲。模式平均結果顯示，堤長、天空能見度、植覆等級及底質種類是六項環境變數中相對較重要的。 本研究確認岸鳥在魚塭環境下的群棲地利用具選擇性，所有物種與類群的岸鳥在魚塭環境中會選擇長度較長、距覓食地較近、能避風且天空能見度較高的堤岸群棲，以降低掠食風險並節省能量花費。不同物種對於堤岸的植覆程度有相反的偏好，可能是由於類群1的岸鳥在群棲時除了以成群作為避敵策略外，同時利用植覆增加自身的隱蔽性。過去許多研究探討岸鳥的成群避敵行為，卻較少探討不同岸鳥的避敵策略差異，未來值得針對此現象做更進一步之觀察與研究。六項環境變數中，掠食風險相關的堤長與天空能見度是影響岸鳥群棲地選擇的主要環境變數之一，顯示出魚塭環境由於被許多人為建物切割且存在較多視覺遮蔽，缺少自然海岸中連續大面積且空曠的群棲地，可能使岸鳥在此環境群棲面臨較高的掠食風險。

The habitats of shorebirds can be divided to foraging habitat and roosts, the latter is the area in which shorebirds rest in flocks when the intertidal flats are inundated during high tide period. The coastal area of Chang-Hua, Taiwan is an important wintering site and also a stopover site on the East Asian – Australasian Flyway. The nutrient rich mudflat in the central west-coast has been the major feeding habitat for thousands of shorebirds. However the neighboring land area is now occupied by man-made landscapes, forcing the shorebirds to roost on aquacultural ponds’ dikes during high-tide. Previous studies conducted in natural coasts indicated that predation risk and energy limitation are the major factors affecting roosts selection. However few studies has been made in aquacultural environment. Thus, the aim of this study is: (1) To verify whether the usage of roosting habitat of shorebirds is selective, and to compare the habitat preferences between different species. (2) To compare the relative importance of environmental variants. Bird surveys were conducted monthly from October, 2011 to May, 2012. The sample area is the aquacultural zone located in Fangyuan Township, Changhua County. Six environment variants of dikes were collected through fieldwork and remote-sensing images. Length, vegetation coverage and sky visibility are the variants related to predation risk. Distance to feeding site, substrate type and shelter are related to energy limitation. Cluster analysis is used upon species of small sample size, to cluster them into groups based on the similarity of the dikes they used. Univariate analysis is used to determine whether there is environment preference of roosts selection. Model analysis is used to compare the relative importance of variants. In the period, 18 species, 52922 individuals were recorded, which totally used 147 dikes as their roosts. Kentish Plover (Charadrius alexandrinus) had the highest abundance and number of dikes used, followed by Dunlin (Calidris alpina). Except these two species, two groups were made by cluster analysis. Group 1 includes Pacific Golden Plover (Pluvialis fulva), Greenshank (Tringa nebularia), Marsh Sandpiper (Tringa stagnatilis) and Redshank (Tringa totanus). Group 2 includes Grey Plover (Pluvialis squatarola), Terek Sandpiper (Xenus cinereus), Eurasian Curlew (Numenius arquata), Great Knot (Calidris tenuirostris), Greater Sand Plover (Charadrius leschenaultii), Lesser Sand Plover (Charadrius mongolus), Ruddy Turnstone (Arenaria interpres), Red-necked Stint (Calidris ruficollis), Sanderling (Calidris alba), Red Knot (Calidris canutus), Curlew Sandpiper (Calidris ferruginea) and Tattler (Tringa brevipes). The result of univariate analysis indicated that all species prefer to roost on dikes with longer length, higher visibility, shorter distance to feeding site and with sheltered side. The preference for vegetation coverage of group 1 is opposite to other species. The result of model analysis indicated that length, sky visibility, vegetation coverage and substrate are more important than other factors. This study verifies that like in natural coasts, roosts selection of shorebirds in aquacultural environment is also affected by predation risk and energy limitation. Different preference for vegetation coverage among species shows that different anti-predation strategies might be used. Besides flocking, shorebirds of group 1 possibly use camouflage simultaneously as their anti-predation strategy when roosting. Predation risk is the major factor affecting roosts selection of shorebirds. This might be attributed to the characteristic of aquacultural environment, which usually has fewer large roosting area and more visual obstruction than natural coasts due to the existence of complicated artificial buildings.