臺灣黑翅鳶（Elanus caeruleus）族群分布趨勢及預測

Abstract

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.