Group composition and density of free-ranging deer species in Wilpattu National Park, Sri Lanka

This study assessed the group size, population density, and social structures of three sympatric deer species, Spotted Deer (Axis axis), Sambar Deer (Rusa unicolor), and Barking Deer (Muntiacus muntjac) in Wilpattu National Park (WNP), Sri Lanka. Using vehicle-based distance sampling along systematically distributed 5 km transects from 2nd November 2024 to 21st January 2025, density estimates were derived through Distance 7.3 software, while group composition and social structure were analyzed using R software. Spotted Deer exhibited the highest population density (111.34 ± 30.11 deer/km²), significantly surpassing Sambar (8.26 ± 4.48 deer/km²) and Barking Deer (7.47 ± 3.16 deer/km²). Group size analysis revealed that Spotted Deer formed significantly larger groups (mean = 7.48 ± 0.40) than Sambar and Barking Deer, which typically occurred in small groups or solitarily. Group composition patterns further highlighted species-specific social behavior: Spotted Deer were predominantly in mixed groups, Sambar showed a balanced distribution between groups and solitary individuals, while Barking Deer were mostly solitary. These findings underscore distinct ecological and behavioral adaptations among the three deer species, contributing to niche differentiation and species coexistence within the diverse habitat mosaic of WNP. The results have important implications for wildlife management and conservation planning in tropical forest ecosystems.