Habitat selection of a reintroduced beaver population in the Absaroka-Beartooth Wilderness

Abstract

In 1986, a beaver reintroduction program was initiated in the Absaroka-Beartooth Wilderness (AB), Montana, in an effort to restore this species to the landscape after a nearly 40 year absence. Since reintroduction, the AB has been inventoried yearly by the U.S.F.S. Gardiner Ranger District to document the location of active beaver structures. This study utilized the beaver structure inventory to report habitat characteristics associated with successful beaver colonies in the AB over a 24 year period. In meadows along 3rd order streams, colonies beaver established early (1986 - 1993) were more successful through 2010 than those established later (1994 - 2006), likely because habitat selected early was of higher quality. Odds of beaver colony success increased with greater stream sinuosity and depth, less distance to secondary channels, and less area of point/gravel bars. The amount of willow, although abundant at all locations, was not significantly different for beaver colony locations with varying levels of success. The best habitat for beaver colonies in meadows along 3rd order streams appeared to be on or within close proximity of secondary channels (e.g., sloughs, tributaries) because these locations were sheltered from destructive main stem flooding such that colonies and their structures were more permanent. Locations with evidence of historic use by beaver in meadows along 3rd order streams had less area of point/gravel bars, greater stream depth, and more willow than locations which had never been used by beaver. Successful beaver colonies were also found in smaller meadows on 1st and 2nd order streams although there was less available willow and streams could be intermittent in flow. After 24 years, the beaver population appears to be at carrying capacity, although there is no evidence that willow harvest rates are excessive or even negative. The success of reintroduced beaver populations in the AB is in contrast to conditions on the nearby northern Yellowstone winter range, where colony density is lower, likely because riparian woody vegetation shows more evidence of suppression from ungulate browsing, site potential for willow growth may be less, and negative anthropogenic effects persist.