TOKYO, Feb 8 — Bears entered areas near human dwellings despite being adequately nourished, even in 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.
According to Kyodo News, the research team, which included the Tokyo University of Agriculture and Technology and Shimane Prefecture Mountainous Region Research Centre, examined the relationship between acorn availability, the bears’ primary autumn food source, and their body fat levels.
Japan’s recent rise in bear intrusions has often been attributed to food shortages in the wild.
The findings suggest that measures such as removing “attractants”, including fallen persimmons and chestnuts, and blocking bears’ entry routes into settlements are essential, said Shinsuke Koike, a professor specialising in ecology at the university.
The study analysed 651 Asian black bears, one of the two bear species in Japan, that were killed after being deemed threats to human neighbourhoods or in traffic accidents in Shimane between 2003 and 2018.
The researchers cautioned that it remains unclear whether the findings can be applied to other regions with different environmental conditions.
The bears’ nutritional status was assessed using three indicators, subcutaneous, visceral and bone marrow fat, reflecting the order in which fat reserves are mobilised as an animal’s condition deteriorates.
Fat levels peaked in autumn, when bears feed heavily on acorns ahead of winter hibernation, before declining by 62 per cent for subcutaneous fat and 39 per cent for visceral fat in spring after hibernation. Levels fell further from spring to summer amid tighter food availability.
During hibernation, bears are believed to primarily burn subcutaneous fat, which is easier to store and metabolise. As nutritional conditions worsen, they draw on visceral and bone marrow fat.
While visceral and bone marrow fat levels remained low throughout the year following poor acorn harvests, no notable difference was observed in subcutaneous fat levels, the study found.
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.
“These intrusions were likely driven not by poor nutritional status but by the presence of attractive food sources,” the study, published in the journal of the Mammal Society of Japan, said. — Bernama-Kyodo
