[Objectives] Activity rhythms and time budgets are not fixed throughout the life cycle of animals. Instead, animals exhibit adaptability across various dimensions. This adaptability, particularly with respect to the temporal aspects of ecological niches, serves as a viable mechanism for animals to respond to cyclical environmental changes. However, the effects of annual and seasonal cycles on animal activity in the tropics remain unclear, and it is uncertain whether animal activity is plastic. Muntiacus nigripes, a diminutive deer species, inhabits tropical forest ecosystems, yet its natural ecology remains largely unexplored. Therefore, this study examined variations in the activity rhythm and time budget of M. nigripes across different temporal scales. [Methods] From November 2020 to October 2022, 160 infrared-triggered camera traps were deployed in the Jianfengling forest area of National Park of Hainan Tropical Rain Forest, Hainan Province, China to monitor M. nigripes and other wildlife. Based on the recorded infrared camera data, the kernel density estimation method built into the “overlap” package was employed to draw the daily activity rhythm curves of M. nigripes in different years, seasons, and sexes. In addition, we used the “overlapEst” function to calculate the overlap coefficient, and applied the Wald test in the “activity” package to assess the statistical significance of difference of the daily activity rhythm in M. nigripes. We recorded the behaviors of M. nigripes through photos and videos. The time budget of daily activity was expressed as the ratio of the number of samples with different behaviors to the total number of samples. The frequency ratio of daily behavioral time allocation was expressed as the ratio of the number of samples of a behavior in a time period to the total number of samples of all behaviors in that time period. Furthermore, we performed the Mann-Whitney U test to examine differences in time budgets for different daily behaviors between different sexes and between different seasons. All analyses were performed by R 4.2.3. [Results] A total of 2 739 independently valid photos were captured by 160 cameras over 45 719 working days. The results showed that M. nigripes was a diurnal species, mainly active at dawn and dusk.Its daily activity rhythm varied between years and seasons, and the overlap coefficient of daily activity was different between 2021 and 2022 (P < 0.05). Among the seasonal changes of different individuals, only the overlap coefficient of daily activity of male individuals in 2021 showed a seasonal difference (P < 0.05), while the rest showed no significant difference (Fig. 3). The temporal dimension of the ecological niche of M. nigripes showed obvious inter-annual variation in social isolation, with 2021 standing out as a significant period of differentiation. Specifically, during the dry season of 2021, a significant divergence was observed in the overlap coefficient of daily activities between males and females (P < 0.05). Similarly, during the rainy season of 2021, a significant difference was observed in the overlap coefficient of daily activities between sexes (P < 0.05). Conversely, no significant difference was noted in the overlap coefficient of daily activities between males and females in 2022 (Fig. 4). The primary behaviors of M. nigripes were locomotion and feeding, which respectively accounted for 36.2% and 48.1% of the total behaviors of females and 44.6% and 39.7% of the total behaviors of males (Fig. 5). In addition, sexes influenced the diurnal time budget for feeding, grooming, and parental care behaviors (P < 0.05), and seasons influenced feeding behaviors (P < 0.05). [Conclusion] In the natural ecological setting devoid of large carnivores, M. nigripes exhibits signals of releasing activity times throughout the day, demonstrating plasticity in activity rhythm and time budget across sexes and seasons.