Selection of aquatic vegetation in river habitats by Eurasian beaver (Castor fiber) in South-Eastern Norway

Habitat selection in animals is evident when the choosing of habitat is disproportionate to its availability, usually when habitat characteristics differ in quantity and quality. A very important factor of their use is the availability and suitability of food. Herbivores rely on the vegetation around them for food, and semi-aquatic mammals often use both terrestrial and aquatic vegetation to supply their diet. Aquatic plants are referred to as macrophytes in aquatic botany, and are an integral part of lake and river ecosystems, known to impact both biotic and abiotic features of the environment. Beavers (Castor spp.) are opportunistic and choosy generalist herbivores, and will vary their diet with availability and seasonality. Their diet is mainly composed of woody plants such as willows (Salix spp.) and aspens (Populus spp.) during winter, and grasses, forbs and aquatic plants during summer. Aquatic plants are known to have a higher nutrient content than many terrestrial plants, and beavers forage for example on water lilies (Nuphar spp. and Nymphaea spp.), water lobelia (Lobelia dortmanna), horsetails (Equisetum spp.) and pondweeds (Potamogeton spp.). We studied aquatic vegetation composition of diving and available locations in river habitats of Eurasian beavers (Castor fiber) in south-eastern Norway, to see if beavers selected on certain macrophyte communities over others. We did this in eight beaver territories in the Saua river system in Telemark county. We modelled diving probability with generalized linear mixed models, and found that important diving characteristics included depth, distance to lodge and river edge, sediment type and vegetation cover. Unique insights into diving preferences were obtained, but future research is much needed.