Beaver-Dredged Canals and their Spacial Relationship to Beaver-Cut Stumps

Abstract

Castor canadensis Kuhl (North American beavers) are central place foragers who collect woody plants and building materials from their surroundings and return to a main body of water containing a lodge or food cache. It has been suggested that beavers dredge water-filled canals to extend access to foraging areas; however, the possibility that these engineered transportation routes function as extensions to the beavers' "central place" has yet to be considered. Our objective in this study was to gain a better understanding of the formation and utilization of canals by beavers and thus further elucidate the complex foraging behavior of these ecosystem engineers. During 2004–2011, we mapped beaver ponds, canals, and cut stumps in eight groundwater-fed wetlands, from at least four separate colonies, in Indianapolis, IN. We found that the mean length, depth, and width of the beaver-dredged canals were 604.3 6 493.1 m, 28.0 6 22.2 cm, and 107.7 6 107.1 cm respectively. Two of the canal systems were mapped for multiple years and their length, depth, and width increased over time and supported the prediction that beavers continuously "engineer" these canal systems to extend their foraging area into new locations. In addition, and in contrast to previous studies, we found that the number of beaver-cut stumps was negatively related to distance from canals, but not from the body of water containing their lodges. We recommend that studies of optimal foraging in beavers take canals into account, where applicable, when relating foraging to distance from the "central place."