Hainan Island’s Mammals Revealed: 95 Species, Many Facing Extinction Risk

Hainan Island, China’s largest tropical island, has long been recognized as a place where geography and evolution have conspired to produce something extraordinary. Separated from the mainland for millions of years, the island’s forests, mountains, and coastal lowlands harbor a mammalian fauna shaped by long-term isolation, producing species found nowhere else on Earth. Yet the full extent of this diversity has remained surprisingly poorly documented, resting largely on a foundational survey published more than four decades ago. A new study, published in the journal Biological Diversity by researchers affiliated with the South China Botanical Garden of the Chinese Academy of Sciences, now delivers the most comprehensive accounting of the island’s terrestrial mammals to date, and the picture it paints is both richer and more precarious than previously understood.

The research team built their updated checklist on the shoulders of a landmark work: Birds and Mammals of Hainan Island, published in 1983. That volume served as the baseline for virtually all subsequent assessments of the island’s mammal diversity, cataloguing 76 terrestrial mammal species. In the decades since, however, taxonomy has been revolutionized by molecular techniques, museum collections have grown, and field surveys have accumulated a vast body of literature documenting new records and revised species concepts. The researchers systematically synthesized this four-decade archive of published records, museum specimen data, and modern taxonomic frameworks to produce a rigorous, up-to-date inventory of what actually lives on the island.

The result is a checklist documenting 95 terrestrial mammal species, distributed across 9 orders, 26 families, and 63 genera. That total represents 12.91 percent of China’s entire terrestrial mammalian species richness, a remarkable figure for a single island. Compared with the 1983 baseline of 76 species, the new inventory reflects substantial changes in how scientists understand Hainan’s fauna. The team revised the taxonomic status and nomenclature of 40 species, a figure that underscores just how much species concepts have shifted with the advent of integrative taxonomy, which combines genetic, morphological, and ecological evidence to delineate species boundaries more accurately than older, morphology-only approaches.

In addition to these revisions, the researchers added 19 new distribution records for the island, the majority of which involved bats and rodents. These two groups are notoriously difficult to survey and are frequently underrepresented in historical inventories, partly because many bat species are cryptic in the field and several rodent lineages can only be distinguished reliably through genetic analysis. The additions suggest that even for a comparatively well-studied region of China, the true diversity of small mammals may still exceed what is formally documented. At the same time, the team exercised caution: two previously reported species were excluded from the checklist because their distributions fall outside Hainan Island proper or because they lack solid field evidence, a decision that reflects a commitment to verifiable records over inflated species counts.

Beyond simply counting species, the study assessed the conservation status of Hainan’s terrestrial mammals against multiple authoritative reference frameworks, including the IUCN Red List of Threatened Species, the appendices of the Convention on International Trade in Endangered Species (CITES), and China’s national and provincial wildlife inventories. The findings are sobering. Ten species qualify as threatened under IUCN criteria, while 22 species are considered threatened according to the China Red List of Biodiversity. The discrepancy between these two figures highlights how national assessments can capture extinction risk at finer regional scales than global evaluations, which may lag in recognizing the precarious status of geographically restricted populations.

Endemism emerges as one of the island’s most striking features. Seven of the documented species are endemic to China, and six of those occur exclusively on Hainan Island. This concentration of range-restricted species means that the fate of a significant fraction of the island’s mammal diversity rests entirely on the management of a single, relatively small landmass. The most famous of Hainan’s endemic mammals, the Hainan gibbon, has become a global symbol of both extinction risk and conservation hope, but the new checklist makes clear that the island’s smaller, less charismatic mammals face comparable pressures with far less public attention.

The study’s biogeographical analysis confirms a pattern long predicted by island-biogeography theory: Hainan hosts fewer mammal species than the neighboring mainland provinces of Guangdong and Guangxi. Isolation, limited land area, and the dynamics of colonization and extinction all contribute to reduced species richness on islands. Yet the researchers found that Hainan carries a disproportionately high share of critically endangered taxa relative to the mainland. This elevated proportion of imperiled species makes the island’s mammal fauna exceptionally vulnerable to human disturbance and habitat fragmentation, the twin forces that have reshaped tropical Asian landscapes over the past century. When a species’ entire global population is confined to one island, habitat loss there translates directly into global extinction risk.

Compounding the problem is a persistent gap in basic knowledge. Roughly 10 percent of the recorded species remain data-deficient or unevaluated, meaning that scientists lack sufficient information even to assess whether they are threatened. This knowledge gap is particularly pronounced among insectivorous bats and forest-dwelling rodents, groups that are difficult to detect, challenging to identify, and often overlooked by funding priorities that favor larger or more visible animals. For these species, the absence of data is itself a conservation concern, because unassessed populations may be declining unnoticed. The checklist’s authors emphasize that closing this gap is a prerequisite for any credible conservation strategy on the island.

From these findings, the research team lays out a clear agenda for future work. They recommend integrative taxonomic studies that combine molecular and morphological evidence to resolve remaining uncertainties in species boundaries, targeted field surveys aimed at under-sampled habitats and taxa, and long-term biodiversity monitoring programs capable of tracking population trends over time. They further call for strengthened in-situ conservation, which protects species within their natural habitats, and ex-situ conservation measures, such as captive breeding and seed or tissue banks, that provide insurance against catastrophic loss. Finally, they stress that taxonomic and threat assessments must be updated regularly and dynamically, since a static checklist quickly loses its value as new species are described, ranges shift, and threats intensify.

The significance of the new inventory extends well beyond Hainan’s shores. Baseline data of this kind are the foundation of evidence-based conservation planning: without knowing which species occur where, and what condition their populations are in, managers cannot prioritize sites, allocate resources, or measure whether interventions are succeeding. For China’s tropical island province, which has invested heavily in forest protection and in the recovery of flagship species, the checklist provides an essential reference against which future change can be measured. It also serves as a model for other regions where historical inventories, however groundbreaking in their time, have not kept pace with modern taxonomy and accumulated field knowledge. Four decades after the original survey, Hainan’s mammals are finally getting the detailed accounting they deserve, and with it, a stronger scientific basis for survival.

Subject of Research: Updated species inventory and conservation assessment of terrestrial mammals on Hainan Island, China

Article Title: Updated checklist reveals rich, threatened terrestrial mammal diversity on Hainan Island

Article References: Updated checklist reveals rich, threatened terrestrial mammal diversity on Hainan Island. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Hainan Island, terrestrial mammals, taxonomy, species checklist, endemism, conservation, IUCN Red List, biodiversity monitoring, island biogeography, bats, rodents, habitat fragmentation