Delineating seasonality by inferring behavioral states from movement patterns in Asian black bears

Seasonality shapes the timing of life-history events in animals across ecosystems, influencing how species allocate time and energy throughout the year. Yet conventional seasonal frameworks, often derived from environmental cues such as temperature or vegetation phenology, may not align with the behavioral timing experienced by animals in response to changing ecological and energetic conditions. Using GPS tracking data from Asian black bears (Ursus thibetanus) in central Japan, which exhibit pronounced seasonal shifts in life-history transitions, we inferred behavioral states with hidden Markov models to identify behavior-based seasonal phases. The proportion of behavioral states changed progressively from spring to autumn, with an increasing dominance of active states (exploring and traveling) as bears adjusted to reproductive and energetic demands. From late May to late August, females spent a greater proportion of time traveling, whereas males balanced exploring and traveling states, suggesting behavioral differences in mate search during the mating season. Both sexes showed a substantial increase in time spent in the exploring state after late august through autumn, coinciding with their hyperphagic period. These behavioral transitions delineate reproductive and hyperphagic phases of the annual cycle, demonstrating that behavioral dynamics provide a biologically meaningful framework for understanding animal seasonality and its linkage to environmental variability.