Camera traps reveal grouping behaviour and spatio-temporal partitioning patterns of East China sika deer ( <i>Cervus nippon kopschi</i> )

Animal behaviour is the overall response to changes in both external environment and internal physiological processes, and investigating the behavioural rhythms of wildlife is essential for understanding the spatio-temporal dynamics of their activities and the factors shaping them. To understand the grouping and activity patterns of sika deer as well as the mechanisms for coexistence among sympatric species, we analysed the camera trapping data in Taohongling National Nature Reserve (TNNR) from 2021 to 2025. In our study, a total of seven distinct grouping patterns were recorded, with 1528 independent observations recorded. From summer to winter, sika deer exhibited a decline in solitary individual activity frequency and showed a greater tendency towards group-based activity, which may be affected significantly by season and breeding cycle. Daily activity patterns differed significantly among seasons (p < .001): in summer, the activity peak occurred at 4.03 am, with an activity level of 0.45, and the nocturnality index reached 91.15% (nocturnal activity). However, with an activity level of 0.57 (95% confidence intervals [CI]: 0.51–0.69), and the nocturnality index was only 61.40% (intermittent nocturnal activity) in winter, indicating a strategy to optimize energy expenditure in response to seasonal fluctuations in temperature and food resources. Most pairs of species showed high levels of overlap in daily activity rhythms (0.68~0.73), while a seasonal decline in spatial overlap between sika deer and other species with similar diets was observed during winter, indicating potential behavioural or ecological segregation. Overall, these insights contribute to unveiling seasonal temporal and spatial distribution patterns as well as grouping behaviour of sika deer, enhancing our understanding of herbivore behavioural adaptations driven by dynamic environmental changes.