The beaver conquers the Sihl

Beaver: From the wilderness park to Biberbrugg?

200 years ago, the beaver disappeared from Switzerland due to intensive hunting. Thanks to reintroduction projects between 1956 and 1977, the population has developed well again. Today, almost 5,000 animals live in Switzerland.

More beavers in the canton of Zurich

There are around 520 beavers in the canton of Zurich, spread over 165 territories, as the canton's latest survey showed in winter 24/25. The population has tripled since 2008. In the last five years, the increase has leveled off somewhat because the density of territories in the north of the canton is already high and the habitat potential has been exhausted.

Reconquering the Sihl

Now the beaver is increasingly spreading into the southern part of the canton, where it was hardly detected until recently. In recent years, however, many new territories have been added - for example along the Sihl and Limmat rivers. New beaver territories have also been created on Lake Zurich near Wollishofen and Meilen. Despite the heavily built-up banks, there are still suitable habitats for Europe's largest rodent, especially in the reed belt areas. An adult animal can weigh thirty kilos and grow to a length of 1.30 meters.

Enrichment for the Wildnispark Zurich

A pair of beavers have been living on the grounds of the Wildnispark Zurich  in Sihlwald since the beginning of 2024. If you look towards the river from the otter enclosure's visitor pulpit, you can clearly see the entrance to the den. The rodents can also be observed from the bench on the other side of the river - especially at dusk. Binoculars are useful for this. Last year, even young animals could be seen.

But watch out! Beavers and beaver lodges are protected in Switzerland. "You should always keep enough distance", explains Nicole Aebli, ranger at Zurich Wilderness Park. "As beavers dig, you can easily destroy the burrows with your weight and injure yourself in the process."

Beavers promote biodiversity

Beavers are regarded as industrious "master builders of nature". They shape the landscape and thus promote biodiversity. Where they settle, the diversity of species doubles and the number of animals and plants also increases. The habitats they create help to bring back rare plants and animals, such as the kingfisher, the midwife toad and the grass snake.

However, its activities can also lead to problems. For example, when water bodies dammed by beavers flood fields. The Canton of Zurich's beaver office advises those affected in order to minimize conflicts in the long term.

On the way to Biberbrugg?

The beavers living in the canton of Zurich can be traced back to releases in the Aargau moated castle, the Thurgau Nussbaumersee lakes and the Zurich Thurspitz. Beavers have long since returned to the Limmat. Now this population has slowly spread along the Sihl from Zurich's main railway station, where the Limmat and Sihl rivers meet.

Who knows, perhaps the offspring of the Wildnispark Zurich beavers will soon reach the river called "Biber" near Biberbrugg. The "Biber flows into the "Alp" which then flows into the Sihl. Via the "Biber" river the beavers could There they could colonize the moorland area of national importance - Rothenthurm. 

The beaver has already conquered the Horgen Pond (Horgener Bergweiher). It is highly probable that the beaver has also colonized this pond from the Sihl. The outflow of the Horgener Bergweiher the Wüeribach, flows into the Sihl in the Wildnispark Zurich.

For comparison: inbreeding in lynx and beaver

Although there are again many beavers in Switzerland, they are descended from a maximum of 140 founder animals. Their genetic base is therefore relatively narrow. So far, however, no adverse health effects have been observed in the Swiss beaver population. This is in contrast to lynx, which are descended from only ten to a maximum of twenty animals in Switzerland. The Wildnispark Zurich Foundation is currently involved in reintroduction projects in Germany to strengthen the lynx population there. No reintroductions are currently planned in Switzerland.