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Smarter than the average bear: bears use nightfall to avoid hunters

Brown bears are escaping hunters by increasing their nocturnal activities. Yet their adaptations may come at a cost.

These days when hunting season begins in late August, the bears are ready. A recent study found that brown bears in Scandinavia learned to avoid hunters by shifting their activities from day to night. While this change in movement patterns may enable bears to escape direct mortality, the shift may compromise their ability to store enough fat for hibernation.
 
The hunting season in Scandinavia runs from late August to late October and overlaps with hyperphagia, a period when brown bears purge on berries to build fat reserves for hibernation year. Hyperphagia is an eating race that determines a bear’s success during the rest of the year, with females typically consuming enough to increase their body mass by 65%. Bears feed most efficiently in daylight when they can visually choose the ripest and most nutritionally beneficial berries, which is why scientists are concerned that a shift to nocturnal foraging would reduce the bears’ ability to harvest enough food to subsist through hibernation.
 
The study, published in Biological Conservation by researchers from universities in Norway, Spain and Sweden, compared bear activity during the 2 weeks before and after the start of hunting season. Researchers collared and radio-tracked 78 male and female brown bears over 7 years and calculated the distance the bears moved every 30 minutes. After hunting started, bears traveled 21% farther during nightfall, particularly after midnight when bears previously rested in the absence of hunters. In contrast, activities during daylight significantly reduced, most notably during mid-day and late evening. The discovery is especially surprising because the change occurs at a time of year when bears are expected to respond to shortening daylight hours by reducing – rather than increasing – nighttime movements.
 
Research on the effects of hunting on prey behavior has been gaining speed over the past decade, calling attention to changes such as increases in prey alertness, reductions in feeding time and shifts in the timing or location of activity patterns. It is now recognized that prey responses to the fear of hunters – or ‘fear effects’ – can influence prey populations equally or even more strongly than direct mortality from hunting, and can have cascading effects on other species in the food web.
 
The current study indicates that hunting generated similar fear effects for Scandinavian brown bears by reducing resting opportunities and changing activity patterns. Since the hunting season in Scandinavia overlaps with a critical period when bears build fat reserves for hibernation, these fear effects could compromise the bears’ behavior and survivorship in ways that hunting quotas currently do not consider. The research serves as strong evidence that resource management could benefit from conservators more proactively integrating fear effects into management decisions.

 
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© Mihail Zhukov/Veer

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Original Paper

Andrés Ordiz, Ole-Gunnar Støen, Solve Sæbø, Jonas Kindberg, Miguel Delibes and Jon E. Swenson, “Do bears know they are being hunted?” Biological Conservation, 152 (2012): 21-28. DOI: 10.1016/j.biocon.2012.04.006.

Further Readings

Mary M. Conner, Gary C. White and David J. Freddy, “Elk movement in response to early-season hunting in northwest Colorado,” Journal of Wildlife Management, 65 (2001): 926-940.
DOI: 10.2307/3803041
 
Evan L. Preisser, Daniel I. Bolnick and Michael F. Benard, “Scared to death? The effects of intimidation and consumption in predator-prey interactions,” Ecology, 86 (2005): 501-509.
DOI: 10.1890/04-0719
 

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