Three decades of survey data reveal life on Taiwan’s volcanic islets refuge

Off the northern coast of Taiwan, three volcanic islets rise from the sea: Mianhua, Huaping and Pengjia. Two of them, Mianhua and Huaping, form the legally designated Mianhua and Huaping Islets Wildlife Refuge, a protected area whose ecological story has now been distilled into one of the most comprehensive long-term biodiversity datasets ever compiled for a Taiwanese offshore refuge. Published in the Biodiversity Data Journal, the data paper describes Version 1.37 of a dataset containing 20,533 occurrence records across nine taxonomic groups, spanning more than three decades of surveys from 1994 through 2025. The dataset has been released on the Global Biodiversity Information Facility under a CC BY 4.0 license, making decades of previously restricted survey reports openly available to researchers worldwide.

The refuge’s origin story is itself a tale of citizen science shaping conservation policy. In 1994, the Keelung City Government planned to develop the islets as a scenic area, but the Wild Bird Society of Keelung raised concerns about the enormous ecological impacts such development would cause. When the scenic draft plan was released, the society conducted the first documented ecological survey of avian and plant communities at Mianhua and Huaping Islets between May and September 1994. Their findings were proposed to the central competent authority, then the Council of Agriculture, recommending that the islets be designated as a Nature Reserve. In 1996, the Council of Agriculture instead designated Mianhua and Huaping Islets as a Wildlife Refuge, and access has since required prior permission and been restricted to research and educational purposes.

One of the most striking ecological recoveries documented in the dataset followed a simple management decision. To eliminate disturbances from historical livestock farming, goats were removed from Mianhua Islet after the refuge’s establishment in 1996. Over the subsequent decades, the ecosystem recovered naturally, characterised by a clear secondary succession in local plant taxa. Because plant surveys have been conducted using grid sampling across thirteen sample plots and line transect methods from 2008 onward, researchers can now examine this succession quantitatively. The species accumulation curves, plotted in survey order, show that the observed species richness for avian and plant taxa has reached a plateau, indicating that survey effort has largely captured the true richness of these communities, whereas the number of recorded species for other taxonomic groups continues to rise.

The refuge holds a distinction that makes it internationally significant: it is the only known breeding habitat of the Streaked Shearwater (Calonectris leucomelas) in Taiwan. In 2010, the Wild Bird Society of Keelung first recorded breeding nests of the species, and continuous occurrence records have been documented up to 2025. These seabirds nest in burrows near steep cliffs, where they face predation threats from rats while breeding. Due to an overall population decline, the IUCN Red List elevated the species’ status from Least Concern to Near Threatened in 2015, a status that remains in effect. Rat-eradication work and breeding surveys at the refuge help maintain the Streaked Shearwater population, making the site a critical stronghold for a species in trouble across its range.

Although the refuge hosts a breeding colony of the Streaked Shearwater alongside resident species like the Peregrine Falcon (Falco peregrinus), the vast majority of avian species recorded are transient migrants. Situated along the East Asian–Australasian Flyway, the refuge serves as a vital stopover before birds enter Taiwan, offering crucial resting and refuelling opportunities for migratory species. The dataset’s avian records therefore carry significance far beyond the islets themselves, contributing to understanding of migration along one of the world’s major flyways. The spatial coverage of the survey data extends beyond the legally defined refuge boundary, particularly in avian and cetacean surveys, capturing birds along patrol routes between Bachimen Fishing Harbour and the islets.

The refuge’s ecological significance extends into the marine environment as well. The marine area of the refuge overlaps with the Turtle–Northern Islands Important Shark and Ray Area, designated by the International Union for Conservation of Nature, which extends from Gueishan Island in the south to the three volcanic islets in the north. Chondrichthyan species have been recorded through visual observation and Baited Remote Underwater Video in 2011 and 2022 through 2025. Most notably, on 4 June 2022, the reef manta ray (Manta birostris) was sighted, a species protected under Taiwan’s Protected Marine Wildlife List. Because many Chondrichthyan records from video were identified only at the family level due to resolution limitations, they were excluded from the species accumulation curves, illustrating the careful taxonomic standardisation applied throughout the dataset.

The survey programme itself evolved through three distinct administrative stages. Before formal government-funded projects were established, from 1994 to 2005, ecological surveys were conducted by civil society organisations, including the Wild Bird Society of Keelung in 1994, 1997 and 2005 and the Wild Bird Society of Taipei in 2002 and 2003. From 2008 to 2011, surveys entered an early government-funded phase, mainly administered by the Marine National Park Headquarters under the Ministry of the Interior, with organisations such as the Taiwanese Coral Reef Society and National Taiwan Ocean University conducting marine and terrestrial work. From 2012 to 2025, the Keelung City Government administered the projects, implemented by different organisations across years, most recently Ceta explorers Co., Ltd., which has surveyed from 2021 to 2025.

Administrative changes also reshaped the refuge’s management and survey emphasis. In April 2018, the central authority was transferred from the Council of Agriculture to the Ocean Conservation Administration under the Ocean Affairs Council, and subsequent regulatory amendments defining the refuge’s spatial extent were announced by the Keelung City Government in July 2018. The refuge covers 226.38 hectares in total, zoned into a core region comprising the terrestrial areas of Mianhua Islet, at 13.30 hectares, and Huaping Islet, at 3.08 hectares, and a buffer region of 210 hectares of marine area extending 500 metres from Mianhua Islet and 200 metres from Huaping Islet. Following the administrative change, greater emphasis was placed on aquatic ecology, including benthic invertebrates, fish and cetaceans, with cetacean surveys beginning in 2019.

The technical rigour behind the dataset reflects modern biodiversity informatics practice. The data follow the Darwin Core standard, structured as a star schema with one occurrence-based core table of 41 columns and an Extended Measurement or Fact table recording body length measurements for fish collected exclusively through the Underwater Visual Census Line Transect method. For records lacking precise GPS points, the Point-Radius Method was applied, assigning exact centroids with five decimal places while representing spatial uncertainty through the coordinateUncertaintyInMeters field. Scientific names were validated using NomenMatch and the Catalogue of Life in Taiwan, tools developed by the Taiwan Biodiversity Information Facility, and the data format was checked by the GBIF data validator before publication. Since 2021, quality control has followed a standardised operating procedure ensuring experienced surveyors, no duplicate individual sightings and verified GPS coordinates.

The dataset also documents the subtle taxonomic challenges of field identification. There are 1,070 unique scientific names but 1,072 unique taxon identifiers, a discrepancy arising from indistinguishable species complexes in the field. The genus Phylloscopus, the leaf warblers, corresponds to three different identifiers: one for the Arctic Warbler complex, one for the Blyth’s, Claudia’s and Hartert’s Leaf Warbler complex, and one for general Phylloscopus species that could not be assigned to either. To adhere to Darwin Core, the scientific name was kept at the genus level, with the ambiguity resolved through vernacular name, verbatim identification, identification qualifier and taxon remarks fields. A similar approach was applied to the Japanese bush warbler complex. As an open-access resource, the dataset now improves cross-border data integration and exchange, supports ecological research on volcanic islets within the Ryukyu Arc, and will be continuously updated as future annual surveys are completed, ensuring that this small refuge’s biodiversity story keeps growing.

Subject of Research: Long-term biodiversity survey data of the Mianhua and Huaping Islets Wildlife Refuge, Taiwan

Article Title: Long-term biodiversity survey data of Mianhua and Huaping Islets Wildlife Refuge, Taiwan

Article References: Chang, J.-W., Tsai, H.-H., Liu, M. J.-Y., Hung, C.-H., & Huang, Y.-T. (2026). Long-term biodiversity survey data of Mianhua and Huaping Islets Wildlife Refuge, Taiwan. Biodiversity Data Journal, 14, Article e209979. https://doi.org/10.3897/bdj.14.e209979

Image Credits: AI Generated

DOI: 10.3897/BDJ.14.e209979

Keywords: Mianhua and Huaping Islets Wildlife Refuge, Streaked Shearwater, biodiversity dataset, GBIF, species accumulation curves, secondary succession, East Asian–Australasian Flyway, Important Shark and Ray Area, Manta birostris, Darwin Core, Taiwan, wildlife refuge