淡水河度冬水鳥族群的長期趨勢

Abstract

水鳥是淡水河重要的生態資產，過去已有許多局部樣區內的短期族群變動研究，推測淡水河的水質惡化、陸域化，可能致使水鳥族群下降。但遷徙性的水鳥族群，同時受到在地與國際因素影響，須先釐清何者扮演較重要的影響因子。此外，鳥群會在各樣區間移動，單一樣區的狀況無法代表整體淡水河的狀況。因此本研究以整條淡水河下游為群聚單位，藉由長期族群資料，試圖從水鳥的生物特徵，解釋族群變動的原因。 本研究以1991至1995、1997、1999及2011八年的冬季資料（11月至隔年2月），涵蓋挖子尾、關渡、社尖、社淡、成子寮、蘆洲、華江橋、華中橋、中正橋等九個樣站，以廣義線性模型進行卜瓦松迴歸，建立27個常見物種20年的長期趨勢。另以七項分屬棲地偏好、食性及國際因素等三大項水鳥生物特徵，與長期趨勢指數進行單變項及多變項分析，找出較能解釋族群趨勢的生物特徵。之後將研究尺度縮小至樣區內，檢視樣區尺度與整體尺度的狀況有何異同，以及不同生物特徵類群在樣區間的分布差異，更全面性地了解淡水河的狀況。 研究結果發現，27個常見物種的長期族群趨勢，10個物種顯著增加（P<0.05），另僅紅嘴鷗及小水鴨此2物種顯著減少。樣區尺度的結果顯示，僅關渡及蘆洲有較佳的水鳥族群狀況，其他樣區中多數族群趨勢卻在下降。原因探究方面，廣狹食性是最重要的因素，狹食性物種有較差的族群趨勢；在度冬地的棲地偏好是次重要的因素，鹹水型物種相較廣適型有較差的族群趨勢。本研究推論，水質汙染可能是造成狹食性物種族群狀況較差的原因。輔助的地景資料則證明，棲地陸域化使部分樣區棲地劣化，卻並非淡水河下游整體面臨的問題。至於國際因素，包括國際族群趨勢、度冬地區域、繁殖地區域、在繁殖地的棲地偏好等，都不是解釋族群變遷的重要因子。 本研究釐清淡水河各鳥種20年的族群趨勢狀況，以及水鳥在淡水河內分布情形的改變；生物特徵分析的結果雖然對於水鳥面臨的環境問題僅能作出推測，但已能肯定在地因素相較國際因素是較重要的影響因子，且應與食物資源有關，並可建議未來持續針對狹食性及鹹水型這兩種族群狀況較差的物種進行監測。此外，這樣的研究若能擴展至全台灣的尺度，將對台灣整體的水鳥狀況，以及台灣在東亞遷徙線上扮演的角色，有更全面的認識。

Waterbirds are one of the important natural resources of Tamsui River. There have been many studies focusing on short-term population change of them, mostly based on single sample site. Those studies suggested that pollution and terrestrialization might be the causes of population decline. But population trends of migratory waterbirds are affacted by both local and global factors, it should be verified in the first step. Besides, the trend within a single site doesn't represent the situation of the whole Tamsui River. Therefore, this study regards the populations at downstream of Tamsui River as one community, constructs long-term population trends, and explains the interspecies differences of population trends by biological traits. The data of waterbirds in wintering season (Nov. to next Feb.) are collected from 1991 to 1995, in 1997, 1999, and 2011, covering 9 sample sites. The long-term population trends of 20 years of 27 common species are constructed using poisson regression log-linear model. Then univariate and multivariate analysis are conducted between population trends and 7 biological traits, related to habitat preference, food preference, and global factors, identifying the biological traits that better explain population trends. The study also replicates the analyses on the scale of individual sample sites, attempting to find out the differences between different study scales. In the results, most of the long-term population trends of 27 common species are positive, 10 species have significantly increased (P < 0.05), only 2 species, common teal and black-headed gull have significant decreased. The results on the sample-site scale indicate the Guan Du and Lu Zhou support more waterbirds now, but most populations in other sample sites have decreased in the past 20 years. Among all biological traits, food preference explains the population trends best. Compared to food generalists, relying on both coastal and freshwater habitats, the species depending only on coastal habitats have more negative population trends. The study As to global factors, including global population trend, wintering location, breeding location, and habitat preference in breeding location, can't well explain the trend in Tamsui River. This study is the first one which constructs the 20-years-long population trends of waterbirds in Tamsui River. It also provides suggestion for monitoring those species that are food specialists or coastal-habitats-dependent in the future. Besides, the methods of this study can be applied to those studies focusing on waterbird populations of Taiwan.