Japan Study: Well-Fed Bears Still Venture into Human Settlements

By Morio Kodama / Yomiuri Shimbun Staff Writer

16:49 JST, April 5, 2026

Bears enter human settlements even when they are well nourished, according to a research team. The team leader said this overturns the common belief that the animals only venture into populated areas due to a shortage of food.

A research team led by Seigo Sawada, head of the wildlife management section at the Shimane Prefecture Mountainous Region Research Center, compiled the findings. Sawada also serves as a reviewing committee member on an Environment Ministry expert panel on bear protection and management.

Checking fat levels

In addition to Sawada, the research team included Prof. Shinsuke Koike of Tokyo University of Agriculture and Technology and other researchers. From 2003 to 2018, the team measured the fat levels of 651 Asian black bears in Shimane Prefecture that had either been removed near communities or killed in traffic accidents.

The results showed that in October of 2004, 2008, 2010 and 2016 — all years when acorns, a main autumn food source, were in poor supply — the bears’ average visceral fat ratio stood at 40%. This percentage exceeded the 35% threshold generally regarded as an indicator of good nutritional condition. The figure was also 40% in May and reached 60% in December for the years with poor acorn supply. In years of abundant or an average acorn amount, the December figure was 50%.

Cutting down fruit trees

According to Sawada, bears continue searching for food even when they are in good condition in terms of nutrition because they try to store as much fat as possible before hibernation. He said they come into human settlements because food is available.

On the other hand, bears in good condition face less urgency to eat. “If there is no food in areas where humans live, there is no advantage for bears to come out,” Sawada said. “If steps such as cutting down neglected fruit trees are carried out thoroughly, sightings of bears can be reduced.”

The study also found that the visceral fat ratio of bears appearing in human settlements was higher in poor crop years than in years with more abundant yields. Acorn-producing trees often have a poor harvest after a bumper crop year. Sawada speculated that fat accumulated during the previous autumn is used gradually over the course of the year. “The higher visceral fat ratio in poor crop years may be because the bears were able to consume a great deal of food the year before,” he said.