Using a spatial mark-resight model to estimate the parameters of a wild pig (Sus scrofa) population in Singapore.

The wild pig (Sus scrofa vittatus) is the one of the largest mammals in the tropical urban city-state of Singapore, after recolonising the main island in the early 2000s. Currently, little is known about the pig population except that it is not naturally regulated due to the extinction of its natural predators, and the absence of hunting and regular culling practices in Singapore. This study was conducted to estimate the population size and distribution of wild pigs in the Central Catchment Nature Reserve (CCNR) of Singapore (Total area: 32.36 km(2), land area: 24.94 km(2)) using a spatial mark-resight model. The CCNR is Singapore's largest reserve and contains the last remaining patches of primary lowland forest scattered within an extensive matrix of secondary forest. From August to September 2016, 40 individuals were tagged and released. From September to November 2016, the 27 camera points setup throughout the CCNR re-captured two tagged individuals and 375 unmarked individuals. The estimated population size was 163.46 pigs and the density was 1.63 pigs/km(2). These estimates were lower than known densities in similar habitats in other countries and may result from the population not having reached its carrying capacity and previous culling events. The density map suggested that resources arc clustered on the eastern side of the CCNR. Repeated measures of the population abundance should be carried out to determine if the population is increasing or stable. Given that pigs are omnivorous and can exploit a wide range of food types, dietary studies should be conducted to determine the food types exploited by the pigs in the CCNR.