Their work usually happens in the dead of night. But, if you look across Yellowstone’s landscape their presence is hard to miss. Beavers, with their dam building, have the ability to change an area’s environment like no other creature besides maybe humans.

Meadows become ponds; streams that were once lined with mature trees have only stumps to remind us of the past. The effects of these changes have far reaching consequences. The habitat that is created can have benefits for flora and fauna at every level of the wilderness. New wetlands promote the growth of willows, aspens, cottonwoods and water lilies. These new food sources attract, insects, birds and large mammals like the moose.   

Beavers are North America’s largest rodent and they can weigh anywhere from 30 to 60 lbs. They live in colonies with 6-13 family members per lodge. Their flat tail is used to pack mud around lodges and dams. They also can be heard slapping their tail on the waters surface when they feel threatened. Today, Yellowstone is home to approximately 500 beavers and 85 lodges. Those numbers indicate a substantial increase in recent years. There is much debate among researchers as to the cause of the increase.

Some believe that the serge in the beaver population can be tied to wolf reintroduction. Wolves were gone from Yellowstone for 70 years. In their absence, elk could forage in one area for longer periods. Many shoots of plants like willow would be eaten before they established and became a viable food source for beaver. With the return of wolves, elk move more frequently and utilize food sources that are not in the open. This small change in elk behavior enables the willow and other brush as well as young tree seedlings to reestablish along streams.

Others believe that climate change is the major factor in the serge of both beaver and willow. With warmer summers, plants have a few more weeks to mature each season. The longer season may allow plants to produce chemicals that make them unpalatable to elk. While more research could give us some answers, more than likely it is the combination of these changes that have led to an increase in the beaver population.

The best beaver habitats today seem to be in the upper Yellowstone River south of Yellowstone Lake, the Bechler region in the southwest corner of the park, and along the Madison and Gallatin Rivers on the west side. Along the main park roads you are most likely to see beavers south of Mammoth in the Gardner River drainage and in Hayden Valley. Be sure to dress properly, even on the best of days the weather can change here in a hurry.

By trying to understand how population dynamics change in a species like beaver we realize how fragile the ecosystem is. In nature, everything affects everything.

Video © 2008 Yellowstone Park Foundation