邊緣效應對於福山鳥類群聚的影響

Abstract

本研究係探討邊緣環境對於鳥類群聚的影響。研究地點位於台灣北部福山試驗林海拔650至850公尺之間，於試驗林的植物園區和周圍的闊葉森林內部分別設置調查樣區，於1995年3月至5月以固定寬度穿越線法調查繁殖季之森林鳥類密度與分佈，記錄鳥類棲息的植被位置與混群狀況，並且採用周蓮香教授的資料以增加採樣數；在1995年3月到8月追蹤覓食中的鳥群，估計其移動速度，以鳥群移動速度和鳥類混群數作為食物豐富度的指標；於1995年7月到8月在森林內部與邊緣放置人工鳥巢，以此評估鳥類繁殖時掠食者對於鳥蛋的捕食壓力。 調查期間內共發現43種鳥類，本研究只分析其中較常見的21種。邊緣處鳥類的密度和出現的鳥種數都比森林內部高，由鳥類密度之差異以及鳥類分佈的狀況，鳥類可分為偏好森林邊緣者（15種）、偏好森林內部者（3種）以及沒有偏好者（3種）。以食性和活動層次，福山的鳥類可分為8個生態同功群，其中樹幹啄木者、灌叢食蟲者、地面雜食者、樹層雜食者和肉食猛禽等五者偏好邊緣環境，空中食蟲者、樹層食蟲者和地麵食蟲者沒有明顯偏好。 在邊緣處，鳥類混群的群數較少以及鳥群移動速度較慢都顯示邊緣地區的食物資源較豐富，人工鳥巢實驗則顯示森林內部位於喬木和灌叢上的鳥巢其鳥蛋比邊緣處容易被掠食者捕食，地面巢則沒有顯著的差異，邊緣地區鳥巢寄生者（筒鳥）亦較少被發現。這些原因都可能與邊緣地區鳥類較多有關。

This study concerned the effects of edge on the breeding bird community in low-elevation Fushan forest area in northern Taiwan. Bird density was censused along edge habitats and in the forest's interior using fixed-width transect line method from April to May in 1995. The locations of birds in forest stratum and mixed-species flocks were also recorded during the censuses. In order to increase the sample size, I use the data of Professor Chou's investigation, too. I estimated the speed of feeding flock of birds from April to August. The speeds of flocking birds and the mixed-species flocks were used to be the indexes of the relative abundance of food resources. The artificial nest experiment was performed to examine predation on bird's nest from July to August. 43 bird species were found in my study area. I analysis 21 species that were more abundant. The densities and the species abundance of the bird community were richer in the edge habitats. According to the differences in density and the distribution pattern of birds in the edges and interior of the forest, I classify 16 species as edge species, 3 as interior species and 3 as general species. Birds were divided into 8 guilds by their diet and activity stratum according to the information of previous studies and my data. In the 8 guilds, trunk probing insectivores, understory insectivores, ground omnivores, upperstory omnivores and carnivores appeared to prefer edge habitats, while upperstory hovering insectivores, upperstory gleaning insectivores and ground insectivores showed no preference. The number of mixed-species flocks and the speed of feeding flocks revealed that the food resources were more abundant in edge habitat. The artificial nest experiments showed that the predation rates of nests on scrubs and trees were higher in the forest interior than in the edge, while the predation rate of the nests on the ground did not vary between the edge and the forest interior. Besides, the nest parasite was more abundant in the forest interior than in the edge. Hence the preference of birds toward the edge habitats may be due to the more abundance of food resources and lower predation and nest parasitism on bird's nests.