Beaver Lodge Occupancy
Beaver Lodge Occupancy Surveys
By Larry Roy. Banner photo Phil Walker.
In the late winter/early spring of 2021, some 30 volunteers - including at least 13 Friends of Elk Island members and some very dedicated parks biologists, performed beaver lodge occupancy surveys in Elk Island National Park. These surveys were performed in support of a larger program run by Dr. Glynnis Hood, professor of Environmental Science at the University of Alberta, Augustana Campus, and Manager of the Miquelon Lake Research Station.
Why beaver surveys? Beavers are semi-aquatic mammals that play a crucial role in shaping the landscape in and around the Beaver Hills. The dams they make create wetlands that support diverse floral and faunal communities and contribute to the knob and kettle formations that abound in this area. The trees they cut down allow shrubs, herbs and grasses room to grow, further increasing the biodiversity across the landscape. Therefore, the health of beaver populations is an indicator of the heath of ecosystems in the Beaver Hills region.
Surveys in areas that had not been sampled before involves first finding all the marshes that might support beavers. This is easily done using satellite imagery. The next step, a much more difficult one, is actually accessing those spots, which is mostly done on foot through thick brush. Once reached, the GPS locations of beaver lodges are recorded so they can be surveyed again in the future.
Beaver use of a lodge is determined by a series of clues; lodges are considered occupied when a fresh feed pile is adjacent to the lodge (Figure 1) and fresh cut trees and stumps are evident on the nearby shoreline (Figure 2). Occupied lodges are also usually devoid of growing vegetation and have new mud deposits (Figure 3).
Figure 1. Occupied beaver lodge with feed pile on the left. (Photo by Kristi Roy)
Figure 2. Older beaver cuttings on left verses fresh cuttings on right. Notice the difference in colour between fresh cuttings (yellowish) and older cuttings (grey). (Photos by Larry Roy)
Figure 3. Occupied beaver lodge showing lack of vegetation growth and fresh mud on the lodge. (Photo by Kristi Roy)
Surveys are very enjoyable as they incorporate challenging exploration of new territory. There are also risks in the physical demands of trudging through often-deep snow and working in remote areas with generally poor or no cell coverage. Another danger is the thin ice between the lodge and feed pile as a result of persistent beaver activity. Although the ice on most of a pond may be as much as 30 inches thick, the ice in and around the feed pile may be only a few inches thick or there may even be open water (Figure 4). These risks can easily be mitigated by working in pairs or groups and by “NEVER” walking over feed piles.
Figure 4. Beaver lodge showing open water (right foreground) in the feed pile as a result of beavers swimming back and forth from their house. (Photo by Norm Cameron)
This was the first time such a large-scale survey (from Miquelon Lake Provincial Park in the south to Elk Island National Park in the north) was attempted. In total, at least 15 protected areas were surveyed (several were surveyed for the very first time) and over 2,100 beaver lodges were identified and classified. This number does not include hundreds of ponds where beaver lodges were thought to exist based on aerial imagery, but none were there. In other cases, old lodges found on previous surveys had since disappeared, but there were often many new lodges found in these areas. In total, 615 active lodges were identified within the study area, as well as 300 ponds with muskrat huts.
Figure 5. Map of Beaver Hills Biosphere showing beaver lodges surveyed in 2021 (pink dots) and beaver lodges not surveyed (blue dots).
(Figure courtesy of Dr. Glynnis Hood)