Dispersal and Habitat Selection of Beavers in Lake Systems
Beavers are keystone species whose foraging and construction activities can dramatically affect
vegetation communities (both terrestrial and aquatic), nutrient loading, and the abundance of coarse
woody debris in the vicinity of their lodge. Thus understanding how and where beavers disperse,
establish territories, and build lodges and dams is important to understanding spatial patterns in beaveraffected processes.
In contrast to the classic beaver pond system, beavers in large lake systems typically do not
maintain a dam but construct lodges along the lakeshore. Beavers likely select lodge sites based on
forage availability as well as abiotic factors such as the amount of wind and wave action (fetch),
substrate type, and water depth sufficient to ensure safe underwater access to the winter food caches.
In some managed lakes, beavers also must contend with decreasing water levels during the main period
of lodge occupancy (winter). We analyzed field-based and remotely-sensed data from 54 beaver lodges
from two managed lakes in Voyageurs National Park (VNP) to identify factors affecting beaver lodge site
selection in large lakes at the macro- and microhabitat scales. At the macrohabitat scale, beavers
selected for deeper water at entrance and for clay/mud substrates, and selected against deeper water
at 10m from entrance and increased fetch. At the microhabitat scale, we found similar water-level and
substrate effects, but also a slight decrease in selection for vegetation indicating abiotic factors may be a
more important driver than vegetation at this scale. Beavers showed stronger selection for deeper
water in the lake that experienced a large overwinter water level drawdown. Our results have
implications for predicting beaver habitat suitability in large lakes that are common throughout the
Canadian Shield, and understanding the ecological effects of artificial water level management.
Beavers typically disperse from natal areas between 2–3 years of age. Mean dispersal distances
reported in the literature have generally not exceeded 10 km in northern systems, as predation risk
from wolves and bears limit overland travel. Six hundred thirty-five (635) beavers were ear-tagged from
2006–2012 in VNP, an 88,000-ha protected area dominated by large, interconnected lake systems.
Trapping is not allowed in VNP and beaver densities exceed 1.0 lodges/km2. Fifty-five (55) ear-tagged
beavers were reported legally trapped outside of the park between 2008 and 2012, of which 48 were
determined to be dispersal events. Mean (±SE) estimated dispersal distance by water was 31.4 km (±
3.8). Maximum dispersal distance was 99.9 km, with 10 others also exceeding 50 km. Dispersal was
female-biased (62.5% of events), and females also dispersed farther than males (35.0 ± 5.0 km versus
24.2 ± 5.0 km). Timing of dispersal events by beaver age class and time of year will be discussed. Results
suggest that long-distance dispersal by beavers is facilitated in hydrologically-connected systems, and
that VNP acts as a source of ecological services that can influence an area 6 times the size of the park.