Bears eat a wide variety of foods. However, rarely have we been able to determine the relative contribution of those foods to growth, reproduction, and the well-being of wild bears. A relatively new technique called stable isotope analysis does allow us to use a few hairs, a drop of blood, or a flake of bone to quantify which foods are being used by a particular bear. This technique can be used on both modern bears and on bears that died thousands of years ago. For example, we’ve learned that grizzly bears currently living in Yellowstone National Park have about the same diet as their ancestors had a thousand years ago. However, things have changed in other ecosystems. For example, salmon provided 58% of the nourishment for grizzly bears living 100 years ago in Idaho, Washington, and Oregon. This level of salmon consumption is about the same as that occurring today in many populations of Alaskan grizzly bears with access to abundant salmon. Unfortunately, no grizzly bear in Idaho, Washington, or Oregon currently consumes salmon.