The dam-building beaver is an ecosystem engineer whose activities benefit many other animals. According to the latest research findings, their positive impact is not limited to only fish, amphibians, insects and waterbirds; mammals also benefit from the presence of beavers.
In a study carried out at the University of Helsinki, beaver patches were found to host nearly twice the number of mammal species compared to forest pond patches not engineered by beavers. Even the number of individual mammals was more than 10% higher in beaver sites.
In beaver patches, particular increase of mammal activity was observed among otters, pine martens, weasels, and moose. In winter, otters benefit from the unfrozen areas of beaver ponds, where they can more easily dive for fish. Pine martens and weasels, on the other hand, hunt voles, which are more abundant close to beaver ponds compared to ordinary forest ponds.
Another species that gained a distinct benefit from the presence of beavers is the moose.
“Moose can make use of the crowns of trees chopped down by beavers. Beaver ponds have vegetation suitable for moose, such as water lilies, and saplings after the water level has reduced,” says University Lecturer Petri Nummi from the Faculty of Agriculture and Forestry, who has studied the environmental effects of beavers for almost four decades.
The study was carried out in Evo state park in Lammi, Hämeenlinna, in 2017–2018. The figures are based on tracks found in the snow and images taken with wildlife cameras. The beavers living in Evo are North American beavers, introduced into Finland in the 1930s. The indigenous Eurasian beaver was hunted to extinction in Finland in the late 19th century, but that species also has been reintroduced into the country through translocation. Based on a national count in 2017, Eurasian beavers were estimated to number between 3,300 and 4,500, while the number of North American beavers was estimated at 10,300–19,100 (Natural Resources Institute Finland 2017).
Petri Nummi, Wenfei Liao, Ophélie Huet, Erminia Scarpulla ja Janne Sundell. The Beaver Facilitates Species Richness and Abundance of Terrestrial and Semi-aquatic Mammals. Global Ecology and Conservation