Diet
Brown bears are omnivores, and their diet can vary dramatically across their broad range that spans much of the northern hemisphere. For example, bears in Yellowstone National Park in the United States tend to have a comparatively high proportion of ungulate meat in their diet, bears in Alaska utilize fish such as salmon to build and maintain their large body mass, while bears further south in Europe exploit the hard mast that dominates the landscape. Brown bears are opportunistic when it comes to food, and the same is true for the Scandinavian bear.
Spring and Early Summer
During spring, bears need food that can rebuild the body's muscle mass that depleted over the hibernation period, rather than renew its fat reserves for the coming winter. Therefore, protein-rich foods tend to dominate the diet during spring and early summer.
During early spring, bears focus on ants, which are a important food source for the Scandinavian bears. Ant species selected by bears tend to be high in energy content, low in formic acid, and to behave relatively passively when their colonies are disturbed. Altogether, ants make up an estimated 20% of the total annual energy intake of the Scandinavian brown bear.
Newborn ungulate calves are also a very important part of the bear's diet in spring and early summer. Moose calves are the most heavily utilized ungulate by bears in Scandinavia, which are an important part of their diet from mid-May through the end of June. In our Southern Study Area, we estimate that each individual bear older than 2 years old takes about 6.5 moose calves per year, or approximately 25% of all elk calves born in the area. Of these calves, 93% are taken during the first four weeks after birth. In total, moose make up about 14-30% of a bear's annual energy intake. In reindeer herding areas, reindeer calves are also important contributor to bear diet, and a continual source of conflict for reindeer herders. In our Northern Study Area, we estimated each adult bears takes about 10.2 reindeer calves per year.
Bears are generally not very effective predators of adult ungulates, such as moose and reindeer, although they do occasionally prey on them. However, bears are incredible efficient scavengers. For example, they will eat the remains of animals that died during winter, and will also steal kills from wolves, where the two predators overlap. Theft of wolf-killed prey often happens during spring when wolves are preying on larger bodied prey (e.g., last years calves and adults).
Late Summer and Fall
Scandinavia’s abundant berry crop has matured by late summer, and by and large, bears in Scandinavia switch during that time period to the sugar-rich berries they utilize for the remainder of the season. Bears must build up fat reserves for their winter hibernation period, and berries contain high-calorie carbohydrates that are generally easily converted into fat. Bears in Scandinavia prefer (in order of priority) blueberries, crowberries, and lingonberries. An adult bear can eat up to a third of its own weight in berries one day, which corresponds to about 20,000 calories daily. Altogether, berries make up about 45% of a bear's annual energy intake in Sweden.
The situation is different in Norway, however. A study in Nord-Trøndelag showed that only 6-17% of local bear annual energy intake consisted of berries, but as much as 65-87% was from meat, mainly sheep. This illustrates how important the availability of the various food items is for a bear's food choices. Free-ranging sheep are relatively easy for bears to kill, and animal fat can be converted into fat reserves more easily than berries. In this sense, it is not surprising that the bear prefers sheep, and especially the fattest parts of the sheep, to berries. In contrast, there are virtually no free-ranging sheep within the bear's range in Sweden, although bears will scavenge on hunter-killed ungulate remains during the fall in both countries.
