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Background <p>In hibernating mammals, the timing of den entry and exit reflects complex interactions among environment, physiology, and energetic constraints, with important fitness consequences. These timing shifts can alter individual energy balance and survival, potentially scaling up to influence population dynamics under climate change. Reliable estimates of denning timing are therefore important to accurately monitor animal behavior and support management decisions, yet current approaches often rely on GPS telemetry, which is limited by coarse sampling, detection issues, and an inability to distinguish true inactivity from presence at the den site. Here, we test a method using accelerometer-derived activity data to estimate denning phenology in a Scandinavian brown bear population. Our approach uses adaptive, individual-specific thresholds to account for variation in baseline activity, focusing on day-to-day changes to identify the start and end of inactivity periods as a proxy for denning. This provides a flexible, reproducible way to detect den entry and exit, overcoming limitations of fixed thresholds and small sample sizes.</p> Results <p>We compared activity-based estimates with GPS-derived den occupancy and examined variation in denning behavior across demographic groups. The method identified inactivity periods in 360 of 388 bear-winters, but failed to detect clear hibernation start and end dates in 28 cases (7%), which showed unusually high or low activity at the boundaries of inactivity. Den occupancy ranged from September 5 to June 2 (112–260 days), while inactivity periods spanned September 6 to May 13 (83–217 days). Comparisons indicate that bears may arrive at and leave den sites several weeks before and after the main inactive period.</p> Conclusion <p>Activity-based analysis offers a robust way to estimate denning phenology, distinguish true inactivity from site presence, and better understand the timing and variability of bear denning behavior. Our individual-level approach improves accuracy in assessing ecological mechanisms underlying hibernation, enhances interpretation of environmental drivers, and provides a reliable tool for monitoring phenological shifts in response to climate change.</p>

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Using activity data to estimate brown bear den exit and entry dates

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年7月19日

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  • Baptiste Brault,
  • Jeanne Clermont,
  • Andreas Zedrosser,
  • Andrea Friebe,
  • Jonas Kindberg,
  • Fanie Pelletier

摘要

Background

In hibernating mammals, the timing of den entry and exit reflects complex interactions among environment, physiology, and energetic constraints, with important fitness consequences. These timing shifts can alter individual energy balance and survival, potentially scaling up to influence population dynamics under climate change. Reliable estimates of denning timing are therefore important to accurately monitor animal behavior and support management decisions, yet current approaches often rely on GPS telemetry, which is limited by coarse sampling, detection issues, and an inability to distinguish true inactivity from presence at the den site. Here, we test a method using accelerometer-derived activity data to estimate denning phenology in a Scandinavian brown bear population. Our approach uses adaptive, individual-specific thresholds to account for variation in baseline activity, focusing on day-to-day changes to identify the start and end of inactivity periods as a proxy for denning. This provides a flexible, reproducible way to detect den entry and exit, overcoming limitations of fixed thresholds and small sample sizes.

Results

We compared activity-based estimates with GPS-derived den occupancy and examined variation in denning behavior across demographic groups. The method identified inactivity periods in 360 of 388 bear-winters, but failed to detect clear hibernation start and end dates in 28 cases (7%), which showed unusually high or low activity at the boundaries of inactivity. Den occupancy ranged from September 5 to June 2 (112–260 days), while inactivity periods spanned September 6 to May 13 (83–217 days). Comparisons indicate that bears may arrive at and leave den sites several weeks before and after the main inactive period.

Conclusion

Activity-based analysis offers a robust way to estimate denning phenology, distinguish true inactivity from site presence, and better understand the timing and variability of bear denning behavior. Our individual-level approach improves accuracy in assessing ecological mechanisms underlying hibernation, enhances interpretation of environmental drivers, and provides a reliable tool for monitoring phenological shifts in response to climate change.