Preference of Helopsaltes pleskei (Taczanowski, 1890) (Aves: Passeriformes: Locustellidae) on uninhabited islets (Chengdo, Jikgudo, and Heukgeomdo) in South Korea as breeding sites

Abstract

This study was conducted to investigate the habitat and breeding status of the Pleske's Grasshopper Warbler (Locustella pleskei) inhabiting unmanned coastal islets (Cheongdo, Jikgudo and Heukgeomdo) on the Jeju Chuja Marine Provincial Park in South Korea. A total of 13 nesting sites were observed between April 2019 and April 2021. Six Camellia japonica (4 ea), Pinus thunbergii (1 ea) and Eurya emarginata (1 ea) nesting sites were found in the Cheongdo islet. Four C. japonica (2 ea), P. thunbergii (1 ea) and Elaeagnus macrophylla (1 ea) tree sites in Jikgudo islet were found, whereas only three C. japonica sites on the Heukgeomdo islet were observed. During the study period, 36 individuals were observed: 14 in Cheongdo, 10 in Jikgudo and 12 in the Heukgeomdo Islets. Most nesting sites were located in the bushy areas of the inner islets. Thus, birds tended to select nesting locations in response to predation and microclimates to increase reproductive rates and maximize offspring survival. This study highlights the importance of unmanned islands (islets) and the presence of bushy shrubs as important nesting and hiding sites for the ecologically vulnerable Pleske's Grasshopper Warbler.