Rare Vietnamese skinks found near Hanoi as models reveal vast hidden ranges

Two of Vietnam’s most elusive skinks have turned up on forested slopes just outside Hanoi, and new computer models suggest their ranges may be far larger than scientists ever imagined. In field surveys conducted in Ba Vi National Park in July 2023 and August 2024, researchers documented the Vietnam Skink (Plestiodon tamdaoensis) and the Devouring Forest Skink (Scincella devorator) in the park for the first time, adding two poorly known reptiles to the species inventory of a protected area on Hanoi’s doorstep. The findings, published in the journal Herpetozoa, combine traditional fieldwork with species distribution modeling to paint a much broader picture of where these secretive lizards might live.

Plestiodon tamdaoensis has a long and scattered history in the scientific literature. The species was described in 1937 by the French herpetologist René Bourret from specimens collected in Tam Dao National Park in northern Vietnam, and for decades it remained known from only a handful of localities. Today it is recorded from evergreen forests in the Vietnamese provinces of Ha Giang, Cao Bang, Bac Kan, Vinh Phuc, Bac Giang, Hai Duong, Son La, Hoa Binh, Thanh Hoa, and Nghe An, as well as from Hong Kong in southern China, at elevations between 300 and 1,200 meters above sea level. Despite this spread, the International Union for Conservation of Nature currently lists the species as Least Concern largely because so little is known about its true distribution and population status.

Scincella devorator, by contrast, is a much younger species with an even murkier record. Darevsky, Orlov and Ho described it in 2004 from Quang Ninh Province in northeastern Vietnam, originally placing it in the genus Sphenomorphus. In 2011, Nguyen reported the species from Yen Tu Mountain in Bac Giang Province and transferred it to the genus Scincella based on two diagnostic traits: a lower eyelid bearing an opaque window, and a lower secondary temporal scale that overlaps the upper one. Subsequent records from Vinh Phuc and Son La provinces extended its known range, but the species remains endemic to northern Vietnam and is classified as Data Deficient on the IUCN Red List, meaning scientists lack even the basic information needed to assess its extinction risk.

The new records come from Ba Vi National Park, a 10,814.6-hectare protected area that spans Ba Vi District of Hanoi and the Luong Son and Ky Son districts of Hoa Binh Province. The park sits in the subtropical climate zone of northern Vietnam, with an annual average rainfall of 900 millimeters, an average temperature of 21.8 degrees Celsius, and average humidity of 79 percent. Its natural habitat above 600 meters consists of evergreen mixed forest of conifers and broadleaf trees. Survey teams working along two forest trails, one leading toward Vua Peak and another toward the Old Church, searched for reptiles between 8:30 in the morning and 4:00 in the afternoon, collecting specimens by hand under guidelines approved by the American Society of Ichthyologists and Herpetologists.

The Plestiodon tamdaoensis specimen, a subadult collected on 28 August 2024 near the Old Church trail at 810 meters elevation, matched the historical descriptions of the species in every measurable detail. Its snout-vent length was 30.5 millimeters and its tail length 46.5 millimeters. The researchers documented large supranasal scales in contact with each other, frontoparietals touching, an interparietal larger than the frontoparietals, separated parietals, two pairs of nuchal scales, four supraoculars, and a scaly lower eyelid. The animal had 24 rows of smooth midbody scales, 45 paravertebral scales, and 52 transverse rows of ventral scales. In life, its head and body were black with two cream stripes running from head to tail base, its flanks were black-brown with a cream stripe on each side, and its tail glowed bright green above, a striking coloration that fades to brown in preservation.

The Scincella devorator specimen, an adult female collected on 28 July 2023 near Vua Peak at 1,105 meters, was found under a carpet of fallen leaves at mid-morning. It measured 56.5 millimeters in snout-vent length with a 76.1-millimeter tail. Key anatomical features confirmed its identity, including the large undivided opaque window in the lower eyelid that gives Scincella skinks their characteristic appearance, the absence of supranasals, prefrontals separated from each other by the frontal scale, three pairs of enlarged nuchal scales, and 28 rows of midbody scales. In life the animal was lightly brownish gray with a wide black vertebral stripe, two pale gray bands extending from the head to the tail base, and a distinct black stripe running from behind the eye to the hind limb. Both skinks were found in disturbed evergreen forest of medium hardwood and shrub, with humidity between 70 and 85 percent and air temperatures between 26 and 32 degrees Celsius.

To understand where else these skinks might occur, the team turned to species distribution modeling, a technique that uses known occurrence records together with environmental data to predict suitable habitat across the landscape. The researchers compiled all published records of both species from papers, field reports, and proceedings, cleaned the datasets following standard protocols, and used the spThin package in R to remove spatial autocorrelation by thinning localities closer than five kilometers apart. This produced a final input set of just six records for Scincella devorator and eleven for Plestiodon tamdaoensis, small numbers that reflect how rarely these animals are encountered. The team then ran MaxEnt version 3.4.4, a widely used maximum-entropy modeling program, with 19 bioclimatic variables from the WorldClim 2.1 database at 30-arcsecond resolution, restricting the study area to a two-degree buffer around the minimum convex polygon of known localities.

The modeling workflow was carefully tuned for reliability. The researchers tested feature class combinations and regularization multiplier values from 0.5 to 10.0 in increments of 0.5, used 10,000 background points, and applied the jackknife method, which is recommended for species with few occurrence records. Model performance was assessed with the area under the curve, or AUC, a standard metric in which values above 0.9 generally indicate strong predictive power. The optimal model for Plestiodon tamdaoensis used a regularization multiplier of 2.5 with linear and quadratic feature classes and achieved an AUC of 0.9142, while the best model for Scincella devorator used a multiplier of 2.0 with the same feature classes and reached an AUC of 0.8967. Final maps were thresholded using the 10 percent training presence rule to separate suitable from unsuitable areas.

The results were striking. The model predicts that Plestiodon tamdaoensis could occupy roughly 110,000 square kilometers across northern Vietnam and a small area of southern China, while Scincella devorator could range over approximately 130,000 square kilometers spanning northern Vietnam, southern China, and northern Laos. Both predictions encompass all known records, including the new Ba Vi localities, and both dramatically exceed the current IUCN range maps for the species. The authors caution, however, that the relatively high regularization multiplier values mean the final models are slightly generalized, and the small number of input localities means the predictions should be interpreted as potential zones rather than confirmed distributions, particularly at the edges of the mapped areas where populations may not actually exist.

Even with those caveats, the implications for conservation are significant. The models suggest that protected areas across northern Vietnam and adjacent parts of China and Laos, especially those covered by relatively large tracts of forest, probably form important strongholds for both skinks. The new records also bring the total number of reptile species recorded in Ba Vi National Park to 52. The researchers call for targeted surveys in promising but underexplored regions, particularly the Cuc Phuong, Ngoc Son Ngo Luong, Pu Luong, and Pu Hu areas spanning Thanh Hoa, Ninh Binh, and Hoa Binh provinces, and the Dong Son Ky Thuong area in Quang Ninh Province. For two skinks that have spent decades hiding in the leaf litter of Vietnam’s mountains, the message is clear: there is far more suitable habitat out there than anyone knew, and finding the animals that live in it will require looking in the right places.

Subject of Research: New distribution records and habitat modeling of two rare skink species in northern Vietnam

Article Title: New records and modeling potential distribution of Plestiodon tamdaoensis (Bourret, 1937) and Scincella devorator (Darevsky, Orlov & Ho, 2004) in Vietnam ( Scincidae )

Article References: Pham, A. V., Nguyen, A. T., Nguyen, A. M. H., Dao, L. T. T., Tran, C. H. T., Le, M. D., & Nguyen, T. Q. (2025). New records and modeling potential distribution of Plestiodon tamdaoensis (Bourret, 1937) and Scincella devorator (Darevsky, Orlov & Ho, 2004) in Vietnam (Scincidae). Herpetozoa, 38, 13-19. https://doi.org/10.3897/herpetozoa.38.e139606

Image Credits: AI Generated

DOI: 10.3897/herpetozoa.38.e139606

Keywords: skinks, Vietnam, Ba Vi National Park, Plestiodon tamdaoensis, Scincella devorator, species distribution modeling, MaxEnt, herpetology, conservation, IUCN Red List, Scincidae, biodiversity