ABSTRACT
Monitoring populations is critical for understanding how they respond to anthropogenic disturbance and for management of protected areas. The use of passive acoustic monitoring can improve monitoring efforts as it allows for collection of data on vocal animals at spatial and temporal scales that are difficult using only human observers. In this study, we used a multiseason occupancy model to monitor occurrence, apparent extinction, and colonization probabilities of a northern yellow-cheeked gibbon, Nomascus annamensis population with acoustic data collected from mobile smartphones in Dakrong Nature Reserve, Vietnam. Forty-five sites were randomly selected for repeated surveys in 2019 and 2022. At each site, a mobile smartphone was attached to a tree and recorded sounds for 4.2 days and 3.89 days on average, in 2019 and 2022, respectively. We manually annotated spectrograms for the presence of gibbon calls, and we detected gibbons at 24 and 12 recording posts in 2019 and 2022, respectively. Estimated local apparent extinction from occupancy models was high with 67% of occupied sites in 2019 becoming unoccupied in 2022. Apparent colonization was low with ~25% of unoccupied sites in 2019 becoming occupied in 2022. As a result, the apparent occurrence probability declined from 0.58 in 2019 to 0.30 in 2022. If the absence of calls indicates that cells are unoccupied this would mean an alarming decline of the gibbon population in the nature reserve. We suggest that in the areas with high hunting pressure, monitoring intervals should be shortened to at least yearly. In addition, urgent actions, such as patrolling, or gun confiscation, should be implemented to conserve the gibbon populations in Dakrong Nature Reserve and other protected areas with the same management context.
ABSTRACT
Climate change can have many negative impacts on wildlife species, and species with narrow distributions are more likely to be significantly affected. In this study, we used ecological niche modeling for species (MaxEnt software) as well as species occurrence data and climate variables to assess the impacts of climate change on the distribution of the grey-shanked douc-an endemic and rare primate species of Vietnam. We used climate data at the current time and two future times (2050 and 2070). Climate data were generated for two climate scenarios RCP4.5 and RCP8.5, together with three climate models ACCESS1-0, GFDL-CM3, and MPI-ESM-LR. We predicted that the distribution of the grey-shanked douc would be sharply reduced by the effects of climate change. The species' suitable distribution range in the future tended to shift toward the center of their current range and to higher mountainous areas. A larger suitable area, in particular highly suitable areas to the north and west of its current potential distribution range, would become less suitable or even unsuitable in 2050 and 2070. Kon Cha Rang Nature Reserve and Kon Ka Kinh National Park should be given priority in conservation of the grey-shanked douc because they now support important populations of the species and are in the highly suitable area remaining for the species in the future. The establishment of a new protected area for grey-shanked douc conservation should be considered in Kon Plong District, Kom Tum Province, which will be the center of the species distribution range.
