臺灣黑翅鳶（Elanus caeruleus）族群分布趨勢及預測

Abstract

相對多數棲息在森林的留棲性猛禽，臺灣平原開闊地的留棲性猛禽有三種，其中一種為主要分布在旱作農地與草生地的黑翅鳶（Elanus caeruleus）。在非猛禽 遷徙季節，黑翅鳶除缺乏相同生態位階競爭者，棲地也提供牠們充足的食物資源， 使其有可穩定繁殖的優勢。黑翅鳶為近18年來的新記錄種及屬臺灣二級保育類動物，目前此物種分布仍持續擴增，然而其分布趨勢與潛在分布範圍尚未被釐清。因此，本研究搜集臺灣黑翅鳶調查記錄，選擇年均溫、年總降雨量、建物面積、森林面積與草原旱地面積等五項環境變數作為環境因子資料，利用Maximum Entropy、Ecological Niche Factor Analysis 和 Genetic Algorithm for Rule-Set Prediction 三種預測分布模式，建立一平方公里網格的黑翅鳶預測分布圖，並推估此物種族群量。結果發現黑翅鳶從主要分布的嘉義縣鰲鼓開始往南與往北，至2013年除基隆市和南投縣外的其它縣市都有黑翅鳶分布，表示此族群歷年確實由最初的小範圍擴張至大範圍分布的趨勢；模式結果顯示草原旱地面積、森林面積與年總降雨量為預測黑翅鳶分布的重要因子；綜觀模式疊圖的結果，顯示未來族群可能分布的地區主要出現於臺灣沿海至內陸之間草原旱地覆蓋面積較大、每年總降雨量較少、森林覆蓋面積較小、年均溫較高以及建物覆蓋面積較小的低海拔平原與臺地；族群量估算有9725隻。本研究首次整合黑翅鳶的歷年分布資料，了解該物種1998至2013年的族群分布趨勢，並運用預測分布模式建立黑翅鳶未來分布範圍與族群量推估，期望作為建立新記錄種的族群擴散模式與預測新記錄種分布的參考依據。

Of the three raptor species that occupy the open plains, the black-winged kite (Elanus caeruleus) is known to reside in arid farm and grassland. During non-raptor migration season, as there were no other competitors that occupied the same niche as the black winged kite, the kites were able to capitalize on the abundance of rodent prey and breed steadily to increase their population. Black-winged kites are the newly recorded and protected species which still expanding their habitats, however, the population trend of this species and its potential distribution are not well understood. Therefore, we collected distribution data of black-winged kite, and selected five environmental variables: average annual temperature, total annual rainfall, area of building, area of forest and area of arid farmland which may be important for the kite. Then we used three models, including maximum entropy, genetic algorithm for rule-set prediction and ecological niche factor analysis to predict the kite’s potential distribution and estimate their population size. From collected data prior to 2013, we found that black-winged kites expanded their distribution from Aogu, Chiayi into southern and northern Taiwan, then almost expanding across the whole country excluding of Nantou and Keelung in 2013. Most important factors that affected this species’ distributions were area of arid farmland, area of forest and total annual rainfall; According to the ensemble results of three models, the final result also showed that black-winged kites mainly appeared in coastal to plains or basins regions, which contained more arid farmland, lower total annual rainfall, smaller forest areas, higher average annual temperature and less built areas. The population size was 9725. Through this study, we first combined the historical data of the black winged kite to understand their expansion trend from 1998 to 2013, and then used predicted distribution models to build the species’ potential distribution and population size. Present study hope to provide a platform for future studies that may wish to build predict distribution and expansion pattern for newly recorded species.