Low-light activity in fallow deer shows sex-specific seasonal changes in a managed landscape

Diel activity patterns of large herbivores vary with environmental conditions, human disturbance, and wildlife management, yet population-level analyses may obscure sex- and season-specific patterns. We examined seasonal variation and sexual segregation in diel activity of fallow deer (Dama dama) in a managed coastal dune system in the Netherlands characterised by substantial but temporally variable daytime recreation, absence of large predators, and female-focused culling. Using a camera-trap network (49 sites; 1,490 camera-trap days), we analysed 4,114 sexed detections collected during three seasons (rut, post-rut, and birthing). Diel activity was assessed using a diel niche framework accounting for seasonal variation in light availability, complemented by equinoctially anchored kernel density estimates and activity overlap metrics. At the population level, fallow deer consistently selected twilight and night, particularly during rut and post-rut. Sex-specific analyses revealed divergence outside the rut. Females exhibited persistent nocturnality, especially post-rut, whereas males increased twilight and daytime activity during the birthing season, showing that the spring increase in daytime activity was largely male-driven. Activity overlap between sexes was highest during rut and declined thereafter, indicating increasing sexual segregation in diel timing. These results demonstrate that pooling sexes masks sex- and season-specific activity patterns. Although these patterns occurred in a landscape characterised by daytime recreation and sex-biased management, their underlying mechanisms cannot be disentangled from intrinsic behavioural and energetic constraints. Our findings highlight the importance of incorporating sex- and season-specific activity patterns into wildlife monitoring and management.

The online version contains supplementary material available at https://doi.org/10.1007/s13364-026-00903-8.