Co-occurrence of two sympatric galliform species on a landscape-scale

Similar species may co-occur in sympatry because of the partitioning of habitat use and resources at different spatial and temporal scales. Understanding co-occurrence patterns of species may assist in explaining patterns of habitat selection, which is important when planning conservation actions for threatened species. Little is known about the ecological preferences of Asian hill partridges, especially where multiple species co-occur. We quantitatively tested how topography and forest type affect the presence of two sympatric hill partridge species, the orange-necked partridge (Arborophila davidi) and green-legged partridge (Tropicoperdix chloropus) in forested habitats in southern Vietnam, and tested the strength of their co-occurrence at the landscape level. We surveyed the occurrence of both species using line transects. We used Poisson regression and probabilistic models to investigate the habitat requirements of both species and co-occurrence patterns. Our habitat-use models indicate that both species use shallow slopes and mosaic forest, while they tend to avoid steep slopes and bamboo forest. The orange-necked partridge seems to be confined to higher elevations while green-legged partridge is distributed over a wider elevational range. This difference in elevational range seems to drive the differences in habitat use between the two species. The orange-necked partridge appears to be strongly associated with mosaic forest, and moderately associated with evergreen forest, but mostly avoided bamboo forest and was never detected in mixed deciduous forest. The green-legged partridge was able to use multiple forest types. The probabilistic models suggest that these two species do not show significant negative or positive co-occurrence when in sympatry. This is the first quantitative data regarding habitat preferences of these sympatric tropical hill partridges at a landscape scale; we presume that their co-occurrence may be maintained by the partitioning of ecological niches or resources at a finer scale. Further research is needed to identify factors controlling their co-occurrence and potential interactions at a micro-scale. An enhanced understanding of habitat preferences of these species will be beneficial for understanding finer scale distribution patterns between species in the genus Arborophila and Tropicoperdix, especially when multiple species occur in sympatry.