Hunger not driving bears to populated areas in western Japan: Study
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Japan’s recent rise in bear intrusions has partly been attributed to food scarcity in their natural habitats.
PHOTO: AFP
TOKYO – Bears entered areas near human dwellings despite being adequately nourished, even during years when acorns were scarce in their natural habitats, likely attracted by fruit trees left on abandoned farmland, a recent study in western Japan showed.
The research team, which included the Tokyo University of Agriculture and Technology and Shimane prefecture’s Mountainous Region Research Centre, examined the links between acorns – the bears’ main autumn food source – and their body fat.
Japan’s recent rise in bear intrusions
The findings suggest that measures such as removing “attractants” such as fallen persimmons and chestnuts, and blocking bears’ entry routes into settlements are essential, Professor Shinsuke Koike, who specialises in ecology at the university, said.
The study examined 651 Asian black bears, one of the two species of bears in the country, that were killed as threats to human neighbourhoods or in traffic accidents in Shimane between 2003 and 2018. The team said it is unclear whether the findings can be applied to other areas with different environments.
The bears’ nutritional status was measured using three indices – subcutaneous, visceral and bone marrow fat – because when an animal is starving and its nutritional condition declines, it mobilises fat reserves in a specific order.
Their fat levels peaked in the fall when they feed heavily on acorns ahead of winter hibernation, declining by 62 per cent for subcutaneous fat and 39 per cent for visceral fat in the spring after hibernation. The fat levels further fell from spring to summer amid tighter food availability.
During hibernation, bears are believed to first burn subcutaneous fat, which is easy to store and metabolise. As their nutritional condition deteriorates, they use visceral fat and bone marrow fat.
Visceral and bone marrow fat levels remained low throughout the year when acorn availability was poor the previous year, while there was no notable difference in subcutaneous fat, the study showed.
At the study site, years of low acorn production by oak trees were typically preceded by years of good or moderate abundance, and bears entering settlements during those periods were “not necessarily compromised” nutritionally. KYODO NEWS
