The Laotian Rock Rat, Laonastes aenigmamus, was first discovered in 2005 in Lao People's Democratic Republic (Jenkins et al. 2005). The species was recognized as a surviving member of the otherwise extinct rodent family Diatomyidae, known from early Oligocene to late Miocene sites in Pakistan, India, Thailand, China, and Japan (Dawson et al. 2006). The Laotian Rock Rat was previously found only in limestone forests of Khammouane Province, Central Lao (Jenkins et al. 2005, Khotpathoom 2011, Vongsa 2010). In 2011, this species was recorded for the first time from Vietnam on the basis of four specimens trapped by local villagers in the buffer zone of Phong Nha Ke Bang National Park (PNKB NP), Central Vietnam (Nguyen et al. 2012). The discovery of a second population of Laotian Rock Rat in PNKB NP promotes opportunities for conservation for this enigmatic species. However, very little is known about the status and ecology of the Vietnamese population. During 2013 and 2014, we carried out 4 surveys in PNKB NP and adjacent areas to identify the distributional extent and habitat preference of the Laotian Rock Rat in Vietnam. In addition, threats to this species and its habitat were evaluated.

The PNKB NP is located in the western part of Quang Binh Province, which borders Khammouane Province of Lao. The national park is characterized by very specific topographic conditions consisting of precipitous karst ridges, which rise to elevations of around 400 m. Scattered among these ridges are narrow valleys and pockets of igneous rock formations. The limestone karst is almost entirely forested, apart from steep cliff faces. Forest clearance occurs only in flat valleys within the limestone massif and in lowland areas bordering it. The most widespread forest type in the PNKB NP is limestone evergreen forest, but there are also significant areas of lowland evergreen forest distributed on non-calcareous substrate in valleys among the limestone karsts (Le et al. 2012). The climate in PNKB NP area is tropical, hot and humid. The annual mean temperature ranges between 23^oC and 25^oC, with summer maximum of 41^oC and winter minimum of 6^oC. The high annual rainfall averages 2,000 - 2,500 mm, 88% falling between July and December, though there is rain in every month. The mean annual relative humidity is 84% (Le et al. 2012). Because of limestone topography, drainage is complex and there are few permanent water sources.

The range of the Laotian Rock Rat distribution was identified through village interviews and live-trapping. The village interview survey was conducted in three communes (Thuong Hoa, Hoa Son and Dan Hoa) of Minh Hoa District, Quang Binh Province. These communes were selected because only these communes contain primary or little affected limestone forest as preferable habitat of the Laotian Rock Rat and are situated close to locality where the first Vietnamese specimens of Laotian Rock Rat were collected in 2011. During the village interview survey, all previously trapped animals of Laotian Rock Rat or their remains were collected for further laboratory studies.

Based on the results of our village interview survey, 12 areas where local villagers have previously trapped the Laotian Rock Rat were selected for targeted field surveys using cage traps and box traps. After taking morphological characters, all live-trapped animals were released back into the wild at the place where they were trapped. Study of Laotian Rock Rat habitat was carried out in the same 12 areas using transect survey and plot survey techniques. Plots of 10 x 10 m were used for inventory of all trees with height more than 3m, plots of 4 x 4 m for inventory of bush trees of height from 0.5 m to 3 m, and plots of 1 x 1 m for inventory of herbs and tree seedlings less than 0.5 m high.

Food items of the Laotian Rock Rat were identified by examining the stomach contents of 10 preserved specimens, food remnants found in the species dens, and observation of live specimens in semi-wild conditions in natural habitat. Food identification was conducted by taxonomic experts based on morphological characters of food item remains. Threats to population and habitat of Laotian Rock Rat were evaluated based on interviews of local villagers and direct observation of threat signs (traps, hunters, logging, forest clearing, human encroachment) in the species distribution area.

Distribution

The confirmed distribution of the Laotian Rock Rat population in PNKB NP comprises roughly 150 km² and is located in five communes of Minh Hoa District, Quang Binh Province, Central Vietnam. Topographically, the distribution range of the Laotian Rock Rat covers low karst mountains in these communes. The habitat quality of the limestone forest in the areas bordering to the east and to the north of this distributional area has been seriously disturbed and is not suitable for the Laotian Rock Rat. On the other hand, the area to the west of the species distribution range contains a vast area of limestone karst forest which continuously extends to Hin Namno National Biodiversity Area (NBCA) of Lao. It is expected that this area harbors the Laotian Rock Rat, but no surveys on rodents in this area were carried out.

In Lao, Vongsa (2010) indicated that the Laotian Rock Rat was found in five districts of Khammouane Province (Laos) within an area of 4,130 km². The species was most abundant in Phou Hin Boun NBCA, while in two nearby limestone areas (Nam Kading NBCA to the north and Hin Namno NBCA to the east) there are no reports of the species. The distribution of the Laotian Rock Rat in PNKB NP, Vietnam is small and far away from Phou Hin Boun NBCA as well as the species distribution range in Khammuoane province. This implies that the population of the Laotian Rock Rat in PNKB NP may be genetically isolated from other populations in Lao and conservation measures for the Vietnamese population should be of high priority and urgency.

Habitat

Jenkins et al. (2005), Vongsa (2010), and Khotpathoom (2011) reported that in spite of several forest habitat types occurring in Phou Hin Poun NBCA (semi-evergreen forest, vine-bamboo forest, dry deciduous forest, mixed deciduous forest and wetlands), the Laotian Rock Rat was found only in limestone holes and in the vicinity of limestone caves at elevations from 263 to 734 m asl. The slopes surrounding karsts formations are covered with both evergreen trees and deciduous trees with little ground vegetation.

PNKB NP is located along the eastern slope of the Great Annamite Range which has a wetter climate. The forest habitat of PNKB NP is characterized by dense moist evergreen forest with different types such as evergreen forest on limestone above 700 m asl, montane evergreen forest on hills above 700 m asl, evergreen forest on limestone under 700 m asl, evergreen forest on hills under 700 m asl, degraded evergreen forest on hills, tree and scrub savanna on limestone, tree and scrub savanna on hills, agricultural land, and plantations and other land uses (Le et al. 2012). However, the Loatian Rock Rat was found only in evergreen forest on limestone karst under 400 m asl. These data indicate that the Laotian Rock Rat has a very narrow habitat preference which is restricted only to limestone karst covered by evergreen forest, semi-evergreen forest, and mixed deciduous forests.

Threats and conservation

Conservation of the Laotian Rock Rat is a high priority not only because the species is the only surviving member of the otherwise extinct family Diatomyidae that was formerly believed to have been extinct for more than 11 million years (Dawson et al. 2006) but also because both Lao's and Vietnam's populations have a very restricted distribution range and are facing high hunting pressure and habitat disturbance. The Laotian Rock Rat has been listed in the IUCN Red List as Endangered (Aplin and Lunde 2008) and in the Wildlife and Aquatic Red List of Lao (Khotpathoom 2011) for conservation action. In Vietnam, due to its recent discovery in 2011, the species has not been listed in the Red Data Book or any conservation legislative documents.