大安森林公園三種鷺鳥生殖族群變化及棲地利用

Abstract

隨著都市化，部分鷺科（Ardeidae）鳥類開始能夠適應都市環境。鷺鳥體態優美又易於觀賞，但當其在都市覓食和繁殖，有時會有引發衛生疑慮、影響交通安全、造成植被破壞等問題而令人困擾。位於臺北市中心的大安森林公園大生態池人工島是夜鷺（Nycticorax nycticorax）、小白鷺（Egretta garzetta）、黃頭鷺（Bubulcus ibis）的集體營巢地，大量鷺鳥糞便產生的臭味即常引來民眾抱怨。本研究透過調查鷺鳥在大安森林公園歷年與不同季節間族群變化、巢數變化、巢位特徵、繁殖情況，探討公園未來可行的經營管理方法。研究期間為2019年1月至2021年5月，結果顯示三種鷺鳥在繁殖季的數量都有逐年增加的現象，尤其小白鷺與黃頭鷺在2020年的巢數分別是2019年的2.3倍與2.1倍。在繁殖季高峰，單月的鳥巢數量可多達823巢（至少1646隻成鳥），平均每平方公尺0.39巢，其中以夜鷺數量最多，有634巢（占77.0%）。在巢位特徵上，於雀榕（Ficus subpisocarpa）築巢的鷺鳥最多（占52.2%），巢位廣泛分布於樹冠低層至頂層，巢下支撐枝以直徑2公分以下細枝為主。多數鷺鳥僅以公園作為繁殖地，並未度冬。鷺鳥這三年的族群增長可能是受益於公園裡巢材和巢位豐富、食物來源充裕、近年颱風少、捕食壓力小等因素。若以施作可行性與民眾觀感為優先考量，建議控制鷺鳥族群的最佳方式是疏枝，可加強修剪細枝（特別是雀榕）以減少合適巢位，且應於9月至12月間執行以避開鷺鳥繁殖時間。同時還能搭配環境教育提升民眾對鷺鳥生態的認識，以改善其對鷺鳥的負面觀感，使人與鳥能在公園和平共處。

With urbanization, some heron species (Ardeidae) are beginning to adapt to urban environments. Herons are elegant and easy to watch. However, they sometimes cause problems such as hygiene issues, traffic safety impacts, and vegetation destruction when foraging and breeding in the urban area. Hence, they occasionally become a nuisance to humans. Daan Forest Park is in the center of Taipei City, and its artificial island in the ecological pond is a breeding site for Black-crowned Night-Herons (Nycticorax nycticorax), Little Egrets (Egretta garzetta), and Cattle Egrets (Bubulcus ibis). The odor from heron droppings often got complaints from the citizens. This study aimed to understand the population dynamites and number of nests between seasons and years, nest-site characteristics, and breeding conditions of the herons in Daan Forest Park to provide suggestions for park management. The research period was from January 2019 to May 2021. The results showed that the populations of the three heron species were increasing year by year in the breeding season. Especially the Little Egrets’ and the Cattle Egrets’ numbers of nests in 2020 are 2.3 times and 2.1 times higher than the numbers in 2019, respectively. At the peak of the breeding season, there could be 823 heron nests in a month (at least 1,646 adult herons), and nest density was 0.39 nests/m^2. The number of Black-crowned Night-Heron nests was the most among the three species (77.0%). In nest-site characteristics, most (52.2%) herons built nests in Large-leaved Banyan (Ficus subpisocarpa). The nest positions were widely distributed from the lower to the top of the canopy, and the supporting branches under the nest were mainly the twigs below 2cm in diameter. Most herons only used the park as a breeding site and did not spend the winter there. The population growth of herons in the past three years might be benefited from the abundant nesting materials and nesting sites, adequate food sources, fewer typhoons in recent years, and lower predation pressure. Considering the practicability of implementation and public reception, pruning the branches is the best way to control the heron population currently recommended. The amount of pruning of twigs (especially Large-leaved Banyans) could be strengthened to reduce suitable nesting sites, and it should be implemented between September and December to avoid the breeding time of the herons. Moreover, at the same time, park managers can use environmental education to enhance people’s knowledge of heron ecology, change their negative attitudes toward the herons, and make the people and the birds coexist in the park peacefully.