Beavers were hunted so intensely that they completely disappeared decades ago in the area. Without the beavers building dams and thus slowing down the flow of creeks, more and more erosion took place and area that used to be wetlands dried out. With the gradual drying the willow tree disappeared, which is one of the major food sources for beavers. So while beavers are starting to repopulate, they don't move in where there is no food available.

So Philmont is building BDAs in order to slow down the creeks, providing suitable habitat for willows - and once this food source is once again established, the beavers should return and take over maintenance of the BDAs.