TOKYO -- Brown bears bring to mind an image of a classic carnivore -- heavy build with deadly claws, clutching silvery salmon between razor-sharp teeth -- but researchers are finding that the species has been moving toward a largely herbivorous diet. Why?
According to research by institutions such as Hokkaido University and the Research Institute for Humanity and Nature (RIHN), the answer to the puzzling trend lies in the development of cities in Hokkaido that started in the Meiji era (1868-1912).
Jun Matsubayashi, a research associate at RIHN, decided to look into the issue because he "wondered why there were so many herbivorous brown bears in Hokkaido, even though there's an abundance of salmon and deer."
One way to examine the cause is to study the bones of brown bears to precisely measure oxygen, nitrogen and sulfur levels to see how their diet changed over time.
Matsubayashi and his collaborators analyzed 337 bone specimens held at local museums in Hokkaido, dating from the Jomon period to the present.
Development in Hokkaido's eastern region, including Abashiri and Kushiro, began in the 1920s. The researchers divided the bone specimens into three categories -- pre-1920, 1931-1942 during the earlier period of city development and from 1996 onward, after development was complete.
The research concluded that the proportion of land animals and other creatures consumed including deer and insects stood at 64 percent up until 1920, compared to a significantly lower 6 percent figure from 1996 onward. Salmon consumption had also plummeted from 19 percent to 6 percent.
Surprisingly, the proportion of fruits like crimson glory vine rapidly shot up from the 1 percent seen until 1920 to the 41 percent from 1996 and beyond.
Combine their consumption of plants like Japanese sweet coltsfoot and water dropwort with fruits, and the total in 2011 adds up to a whopping 84 percent.
The results were the same for specimens from the southern region, including Sapporo and Hakodate, reflecting a shift toward a more herbivorous diet.
Using 2,000 years worth of data, researchers were able to get a detailed picture of changing dietary habits. The brown bears were carnivorous for an extended period, and started becoming herbivorous beginning in the Meiji era.
But the question remains: Why did they stop eating salmon?
After imperial government rule was restored under the Meiji Restoration, land development commenced in Hokkaido to tap into its resources. Roads, ports and railways were revamped and mining made steady progress.
"The fishing industry prospered as development continued, which in turn led to a dwindling salmon population," Matsubayashi said. "Compounded by dams being built on rivers and streams, my guess is that salmon were eventually unable to make it upstream."
Another factor could be the culling of Hokkaido's wolves that often preyed on cattle.
"Brown bears weren't very good at hunting agile deer, so they would often take them from wolves or pick through leftover carcasses," Matsubayashi said. "Now that the wolves are extinct, the bears are at this point where they occasionally eat dead deer."
For a terrestrial mammal species like the brown bear to so significantly change its diet in the span of a few hundred years is unprecedented, according to Matsubayashi.
A survey by the Hokkaido government in fiscal 2012 indicated that there were roughly 2,200 to 6,500 brown bears in Hokkaido.
"The population of brown bears has not declined," a Hokkaido government official said. "Their ability to breed seems unaffected by their switch to a more herbivorous diet."
There are still wider repercussions to consider, despite the unchanged population level.
"When brown bears eat salmon, the resulting leftovers and feces fertilize the land. You can say that brown bears were filling this role of transfering nutrients from the oceans and rivers onto land," Matsubayashi said.
"So we can't rule out the possibility that human development is affecting not just the diet of brown bears, but the entire ecosystem of the habitats they call home."
Bears are omnivorous mammals that can flexibly adapt their diets to their surrounding habitat. For example, polar bears that live in the barren landscapes above the Arctic Circle feed on a highly carnivorous diet made up of prey like seals, while Asian black bears that inhabit forests lean toward a herbivorous diet centered on plants and fruits.
Neither of these bears are as picky as the giant pandas. Fumio Ito, a consulting staff member at Tokyo's Ueno Zoo, said giant pandas "are thought to have a specialized diet of bamboo and sasa, available all year round, because their ancestors retreated deep into the mountains to avoid fighting for survival with other animals."
In fact, researchers found that since roughly 4.2 million years ago the species' gene which controlled the ability to taste and enjoy meat mutated and became inactive.
Pandas began to switch to a vegetarian diet 2 million years ago -- but even today, they still have the digestive system of a carnivore that lacks long intestines needed to properly digest plants.