Beaver (Castor fiber) in Denmark
The beaver was absent from Denmark for more than one thousand years before the species was reintroduced in October 1999. Eighteen beavers captured in Germany were released at six different sites within Klosterheden State Forest in the northwestern part of Denmark.
Large areas in the country have been drained due to intense agricultural use and forestry. One of the main reasons for reintroducing the beaver was because of its ability to create dynamics in its surroundings. By cutting down trees clearings are made which allow for the growth of light-demanding plant species and by building dams beavers flood areas creating new habitats for many species of insects, amphibians and birds.
Klosterheden State Forest is approximately 7000 hectares of 90% coniferous forest and 10% broad-leaved species planted on former heath land. Small streams run in the valleys and non-coniferous trees growing in these valleys are mainly willow ( Salix sp.), birch ( Betula pubenscens and Betula pendula )and bug myrtle ( Myrica gale ). At several places within the State Forest the streams have been artificially dammed and small lakes and ponds created.
The eighteen beavers released included 12 adults, 4 juveniles and 2 kits less than one year old. Beavers captured within one particular beaver territory in Germany were released at the same release-site in Denmark.
Now - four years later - observations have shown that the population has grown to at least 51 individuals in 13 territories. The beavers have dispersed to areas more than 15 kilometres down stream from the release sites and the private land owners have accepted the presence of beavers on their property.
Monitoring and status
The beaver is nocturnal and therefore observing the animals is a difficult task. Fortunately the beavers’ way of living ensures that their presence is confirmed by a lot of visible evidence such as de-barked branches, dams and scent mounds.
As beaver forage on branches they de-bark them and often leave the branches behind at the waters’ edge but some are used as dam-building material. Short trails lead from the water to foraging sites and tree stumps resulting from beaver felling project from the ground.
In late autumn some beavers make food caches. These are big gatherings of branches secured to the bottom of the lake or stream in front of the beaver den. In this way beavers have access to food even in severe winters where the water freezes over.
Beavers build dams to ensure that the water level always covers the entrance of the den and to facilitate the transportation of both building material and food items. Dams are often built in the core area of the territory. In Klosterheden State Forest the highest beaver dam measures 1,2 metres and the longest meassures 74 metres.
Beavers scent mark by depositing a secretion (castoreum) on scent mounds, which are piles made of mud, debris and plant material scraped together by the beaver. The main function of scent marking is the maintaining of territorial rights. As most scent mounds occur near the den or at territory boundaries it is possible to determine the approximate size on a territory on the occurrence of scent mounds.
Monitoring of the beavers in Denmark include recording of the visible signs of beaver activity in all recognised territories and also by searching the water system for new signs of activity from a canoe or by foot.
Twice a year in April and October an attempt to estimate the population size in Klosterheden takes place. Approximately 30 volunteer observers meet and every observer is assigned an observation spot. For about an hour and a half every morning and night for two days observations are carried out, and the date, time and location are recorded every time a beaver is seen. Based on the beavers size and behaviour also the age of the observed individuals is evaluated and assigned to one of three categories; juveniles, subadults and adults.
By applying this method it has been confirmed that at least 34 kits total have been borne during the four breeding seasons in Denmark. One adult has been recorded dead.