Geographic distribution, population and conservation status of Tragulus nigricans, an endangered mouse deer endemic to western Philippines

The Philippine mouse deer (Tragulus nigricans) is an endangered ungulate species, endemic to the Balabac Islands in the Palawan Faunal Region of the western Philippines. Despite its conservation importance, it has received little attention from local authorities and conservation biologists, with limited studies conducted on the species. Here we provide a preliminary report on the species distribution, population and conservation status, based on our recently completed surveys. We used a combination of line transect distance sampling, opportunistic searching on targeted habitats, and informal community interviews to assess the species’ status. We recorded a total of 25 sightings of mouse deer during our transect surveys. All records, including recent sightings of mouse deer, were from two islands, mainland Balabac and Bugsuk. No mouse deer were recorded on other islands that we surveyed, suggesting that the populations have been markedly reduced due to a nearly complete conversion of natural habitat, such as Ramos Island, or perhaps some islands are too small to permanently support populations. Our analyses revealed that the species occurs at low density (0.219 ± 0.084/ha), particularly on Balabac. The mean population estimate based on Bayesian analysis is 2525 (95% Highest Density Interval, 1635–3461). However, this number is highly uncertain because of the low probability, highlighting the need for more information on the species’ population. Several conservation efforts are being implemented now, but more intensive in situ conservation programs would benefit the species, along with other threatened endemics found in the region.