Lutra 46(2)_Elmeros et al_2003

Monitoring of reintroduced beavers (Castor fiber) in Denmark

The European beaver (Castor fiber) returned to Denmark in 1999 when 18 beavers were released in Klosterheden State Forest District in the northwestern part of the country. A monitoring programme was initiated to trace the population and distribution of the beavers, beaver-human conflicts, and effects on flora and fauna. The status of flora and fauna in the reintroduction area was systematically investigated prior to the beaver reintroduction. By 2003, beavers inhabited the entire catchment basin in which they were released and had dispersed to a neighbouring river system 25-30 km away. Beaver kits were observed every year and the population was estimated at 51 individuals in 2003. The beavers mainly fed on willow scrubs during the winter season and non-woody plants in the summer. No damage was reported in forests or agricultural production areas but the beavers caused minor problems by flooding an arable field, gardens, meadows, and forest roads and by blocking inlets to a fish farm. Few significant alterations of water flow were recorded but the diversity of the wetland biotopes increased. The only negative effects appeared to be a restriction of spawning migration of sea trout (Salmo trutta) by beaver dams in brooks. Other fish species were thought to benefit from the beaver ponds. Ponds enhanced spawning potentials for amphibians and enabled new species of birds to breed in the area. Bats profited by more suitable hunting sites. Occurrence of otters (Lutra lutra) increased but no clear relationship with beaver distribution was demonstrated.