It sounds like a bad joke… “What do bears eat?" Answer: "Whatever they want to.” And that’s basically true.
Bears are omnivores. That means they eat both meat and plants. But bears also have seasonal needs for food based on a hibernation period.
Spring Bears are Opportunists
When bears wake from hibernation, they are sluggish and so look for food that is readily available. Whatever they can find with the smallest amount of effort becomes breakfast.
Over the winter, some bison and elk die naturally (winter-kill) and their carcasses freeze, preserving them until springtime. Waking bears sniff out the thawing meat and feast on an easy meal.
As the kings of Yellowstone, bears can convince wolves to abandon their kills until the bears have had their fill. Then the waiting wolves, ravens, and eagles come back to finish off the carcass.
At the same time, elk and deer are calving. The small calves are easy prey for the bears. Mothers try their best to hide the calves and distract the bears, but a good percentage of young animals become bear dinner each year.
Grizzly bears also like to dig with their long, straight claws and strong shoulder muscles. They dig to raid the stashes of gophers and other rodents. As they dig up and eat pantries of seeds and whitebark pine nuts, they distribute seeds (out the other end) and create plant growth. They also dig up roots and tubers which are high in carbohydrates. In contrast, black bears have short, curved claws that are better for climbing than for digging so they eat less seeds and roots.
In the springtime, nutrient-rich plants bloom such as dandelions, clover, and succulent grasses. Bears add this salad to their meals along with ants they stumble upon on the way.
Summer Bears are Foragers and Thieves
Bears continue to eat “salad” during the summer. To this they add roots, worms, and ripe berries. You may have seen huckleberry jams and pies in gift shops with pictures of bears on the label. That’s because bears love the local huckleberries, and strawberries too.
Occasionally, they will take down a bison or adult elk themselves, but it is so much easier to wait for wolves to kill something and then steal it.
In August they eat millions of moths, high in protein and easy to scoop from beneath tree bark and rocks.
Autumn Bears are Preppers
Before hibernation, bears bulk up with protein so they can last the winter. Elk bucks compete for harems during their rutting season in September and early-October. All this fuss takes a lot out of the usually strong bucks. They get weak from exhaustion and some simply don’t have time to eat so they get eaten themselves. These are the last bites of protein for bears before they head to their dens in November.
Winter Bears Do Not Eat
During hibernation, bears do not eat or drink. They digest their stored fat to get them through the winter.