Mammal and bird species using cavities among forests of different ages on Okinawajima Island in the Ryukyu Archipelago, Japan

Various animals use tree cavities in the northern forest of Okinawajima Island in the Ryukyu Archipelago. However, the cavity characteristics and forest types used by cavity users are not well known. The aim of this study was to reveal the cavity users in natural forests of different ages in northern Okinawajima Island. Camera trap surveys were conducted to identify the utilization of cavities in four <i>Castanopsis sieboldii</i> dominated forests; one 40-year-old, one 70-year-old, and two mature forests. Only a few cavities were recorded in the 40-year-old forest and these locations were limited to the lower part of the trees. Consequently, cavity users were limited to two ground-foraging bird species. In contrast, cavities of various sizes were located at various heights above the ground in the other three types of forests, although endangered mammals such as Ryukyu long-furred rat (<i>Diplothrix legata</i>) and Ryukyu tube-nosed bat (<i>Murina ryukyuana</i>) only used cavities in mature forests. The greatest number of cavity-using bird species were recorded in the 70-year-old forest, and a Ryukyu robin (<i>Larvivora komadori</i>) built a nest in a cavity. These results show that mature forests provide various types of cavities with various functions which are important for diverse animal taxa, and that cavity users differ among forests of different ages. Furthermore, it was observed that cavity availability and use does not recover in 70 years. Cavity users should be considered in forest management not only in the core area, but also in the buffer zone of the protected areas in the future.

琉球群岛冲绳岛北部森林中，多种动物会利用树木树洞。然而，目前学界对树洞使用者所偏好的树洞特征与森林类型尚缺乏充分认知。本研究旨在探明冲绳岛北部不同林龄天然林内的树洞使用者类群。研究采用红外相机陷阱调查法，对4片以Siebold栲（Castanopsis sieboldii）为优势种的林分开展树洞利用监测，其中林分年龄分别为40年生、70年生以及2片成熟林。40年生林分内仅记录到少量树洞，且树洞均位于树干下部，因此其树洞使用者仅为2种地面觅食的鸟类。与之相反，其余3种林分中存在不同大小、分布于不同树干高度的树洞；但诸如琉球长毛鼠（Diplothrix legata）与琉球管鼻蝠（Murina ryukyuana）这类濒危哺乳动物，仅会利用成熟林内的树洞。70年生林分内记录到的树洞利用鸟类物种数最多，且有琉球歌鸲（Larvivora komadori）在树洞内筑巢。上述结果表明，成熟林可提供具备多样功能的多种树洞，这对多种动物类群而言至关重要；同时不同林龄的森林，其树洞使用者类群也存在差异。此外，本研究还观测到，林龄达70年的林分仍无法恢复树洞的可获取性与动物利用模式。未来在保护区的核心区与缓冲区开展森林管理时，均应将树洞使用者类群纳入考量范畴。