Beaver colonies are on the rise in Yellowstone, but biologists aren't exactly sure why. It could be a response to the park's healthy wolf population, or it could be tied into climate change.
    Beavers have a long history in the park, but have experienced cycles in their populations there over the years.
    Years ago, before wolves were returned to Yellowstone and beaver populations were low, I worked on a story about aspen studies in the park. At the time, I learned that the burgeoning elk population was really beating down the aspen, one of their main food sources. Well, apparently they also were beating down willow groves, a key food for beaver.
    Of course, once wolves returned to the park they focused on elk as one of their key food sources. In response, the elk became more skittish and didn't linger in any one area for long. As a result, they didn't browse the aspen and willows as heavily as they once did, and the trees responded with more vigorous growth, which was good for beavers.
    To learn more about what's going on with Yellowstone's beaver populations, check out this story.