臺灣低海拔灌叢鳥類調查：定點計數與霧網捕捉之比較

A Comparison of Bird Point Count and Mist Netting Used in a Lowland Shrub in Southern Taiwan

定點計數法與霧網捕捉法是鳥類群聚調查常用的方法。定點計數法效率高，但不易察覺隱密鳥種。相反地，霧網捕捉法較易調查到隱密鳥種，但必須投入大量人力及時間。兩種方法察覺到的鳥種特性不同，但調查得到的鳥類群聚結構差異卻很少被討論。我們於2012年4月至9月，在臺南市龍崎區海拔約100 m之灌叢與高草地，分別以這兩種方法調查鳥類。我們比較兩種方法得到的鳥類資料，包括鳥種組成、種類多樣性及鳥類的生物與生態特性。調查期間共記錄到17種，513隻次。其中，定點計數法12種，413隻次；霧網捕捉法13種，100隻次。兩種方法得到的種類多樣性類似，但鳥種組成相似性不高，Jaccard similarity index僅0.47。定點計數法不易察覺相對密度較低或不善鳴叫的鳥種；霧網捕捉法則不易捕獲體型較大或相對翼長較短的鳥類。我們認為在低海拔灌叢進行鳥類調查時，單獨採用定點計數或霧網捕捉法，均可能嚴重低估樣區的鳥種多樣性；僅採用其中一種方法調查鳥類，對於結果的詮釋，應特別謹慎。

Point count and mist netting techniques have been commonly used in terrestrial habitats for the purpose of surveying avian communities. However, the difference of community structures measured by both techniques is poorly known. We compared point count and mist netting data collected from the same plot in a subtropical lowland shrub in southern Taiwan from April to September 2012 to evaluate their descriptions of the measured avian communities. We detected 12 and 13 bird species by point counts and mist netting respectively, and totally accumulated 17 species from both methods. Species composition between the measured communities was very dissimilar with only 0.47 of Jaccard coefficient. The efficiency of both survey methods on a particular species was significantly affected by the biological and/or ecological traits of the bird. Birds that point counts failed to detect were usually silent or rare species; whereas birds that mist netting failed to capture were usually large or those with a relatively short wing length. Because both techniques detected different sets of community composition, we argue that using either alone to survey an avian community might seriously underestimate its richness with an incomplete description of that community, and the results should be interpreted cautiously.