觀音山是台灣北端最重要的春季遷移性猛禽過境調查點，亦為了解遷移性猛禽在台灣整體遷移模式的重要一環。本報告為1991 至2010 年間共20 年的調查成果。觀音山遷移性猛禽的主要過境期從3 月初至5 月底，長達3 個月，其中1992、1993、1995、2000~2008 等12 季為整季完整調查，其餘8 季僅部分調查。調查結果共記錄3科30 種猛禽，其中本地留鳥日猛禽3 種、遷移性夜猛禽3 種，其餘24 種為遷移性日猛禽，亦為本報告重點。在過境猛禽數量上歷年單季最大量為1993 年的13,208 隻。種類以灰面鵟鷹與赤腹鷹最多，每季過境數量均可維持在千位數，灰面鵟鷹過境數量以1992 年的6,841 隻最多，赤腹鷹則以2005 年的9,158 隻最多。東方蜂鷹過境數量可達百位數，以2004 年539 隻為最多。其餘種類，除鵟於2004 年曾記錄149 隻外，每季均不及百隻。長期來看某些種類的數量已有消長變化，例如灰面鵟鷹呈現逐年下滑現象，但早年數量稀少的北雀鷹、日本松雀鷹、蒼鷹等於近年有增加的趨勢。觀音山並非台灣春季最主要的猛禽過境點，然而具有獨特現象，包含：(1) 單季過境種類多（平均每季可觀察到15 種遷移性猛禽）；(2) 灰面鵟鷹與赤腹鷹的過境期較其他地區長；(3)其他調查點的稀有種類如蒼鷹、花鵰等，在觀音山為穩定過境；(4) 黑鳶在此有遷移族群；(5) 與其他過境點比較，觀音山猛禽過境的來去方向較多而複雜。

Guanyinshan is the most important spring raptor migration survey site in northernmost Taiwan, also an important key point to realize overall raptor migration pattern in Taiwan. This article presents results of 20 years survey from 1991 to 2010. The spring migration period is about three months from the beginning of March to the end of May. The survey teams have finished 12 complete survey seasons in 1992, 1993, 1995 & 2000~2008 during the past two decades, the other 8 seasons are partial survey only. Thirty species of raptors from 3 families were recorded, including 3 resident Falconiformes species, 3 migratory owls, and 24 migratory Falconiformes species which are the major subject in this article. The highest raptor number counted in one season is 13,208 in 1993. Numbers of two main species: Grey-faced Buzzard (Butastur indicus) and Chinese Goshawk (Accipiter soloensis) can reach thousands in each season.The highest record of Grey-faced Buzzard is 6,841 in 1992 and the highest record of Chinese Goshawk is 9,158 in 2005. Number of Oriental Honey Buzzard (Pernis ptilorhynchus) can reach hundreds in each season, the highest record is 539 in 2004. The others species were all below one
hundred in each season, except that the Common Buzzard was ever recorded 149 in 2004. Based on the long-term survey, the numbers of some species were changing. For example, the number of Grey-faced Buzzard has a trend of decrease, while the numbers of Eurasian Sparrowhawk (Accipiter nisus), Japanese Sparrowhawk (Accipiter gularis) and Northern Goshawk (Accipiter
gentilis) were increasing from very rare in the beginnings of the survey to fairly common in recent years. Although Guanyinshan is not the top survey sites with largest numbers in Taiwan, it has some unique attributes including: A. The average specie number in each season is more than the other survey sites in Taiwan. B. The migration periods of Grey-faced Buzzard and Chinese Goshawk are longer than the other survey sites in Taiwan. C. Northern Goshawk and Spotted Eagle (Aquila clanga) that are very rare in other places are quite regular in Guanyinshan. D. The
Black Kite is regular migratory in Guanyinshan rather than being resident in other places. E. The hawk migration direction in Guanyinshan is more complicated than the other survey sites in Taiwan.