Tøndermarsken is one of Denmark’s most diverse bird habitats.

The special cultural landscape shaped by human hand, and the many wetlands are excellent breeding places for fish and, especially, birds.

Tøndermarsken teems with such outstanding bird life that several areas are nominated bird sanctuaries to protect the birds’ breeding and feeding grounds.

Migratory and indigenous birds

Tøndermarsken is famous for the wide variety of birds that flock here. Geese arrive in thousands, e.g. barnacle, pink-footed, greylag and greater white-fronted geese. Every species of duck and wading bird found in Denmark can be seen here at some time of the year as they migrate through this area, or feed and rest in the marshes.

Many birds of prey are regular visitors to the area, including peregrine falcons, merlins, rough-legged buzzards, hen harriers and white-tailed eagles. Meanwhile, large flocks of small birds, including thrushes, pipits, white wagtails, larks, swallows and finches, also visit the marshes.

Black Sun

A spectacular phenomenon that can be experienced in spring and autumn is the “Black Sun”. Huge flocks of starlings swoop in fantastic formations over the meadows before they settle overnight in reed beds.




Gammel Frederikskog
This is the best-preserved part of Tøndermarsken. It is a breeding ground for redshanks, northern lapwings and black-tailed godwits. Note the innumerable canals and ditches. They form an extensive irrigation and drainage system that irrigates the fields in the summer and drains them in the winter.


Margrethe Kog
Margrethe Kog (a polder) was created when “Det fremskudte Dige (the forward dyke)” was built in the period 1979-1981. From the older dyke (1861), there are breath-taking views over this conservation area. Many birds frequent Klæggravene. In a project subsidised by The Wadden Sea National Park, the water-filled pits that formed after soil was removed to build the dykes are currently being restored to their natural state.


Hasberg Lake lies on the border between Denmark and Germany. From a bird hide on the dyke, birdwatchers have a rare opportunity to get close to life in the reed beds. A very rare species of bird, the black tern, breeds here, as do other species, including the great bittern, western marsh harrier, northern shoveler, gadwall and garganey. The lake is also well-known locality for observing “Black Sun”.

Tøndermarsken Magister Kog

This boggy polder is an area of wetlands that extends from Vidå Stream. It is one of the best-known sites at which to observe “Black Sun”, a natural phenomenon that occurs when thousands of starlings come here to settle overnight in the reed beds. Many birds breed in Magisterkog, including the great bittern, greylag, gadwall, western marsh harrier, spotted crake and all common waterfowl. This area is home to Denmark’s largest population of the bluethroat.


Nørresø Lake and Hestholm Sønder Kog wetlands were established in 2010 to restore spawning and rearing grounds for the houting, a very rare species of fish. However, the project has benefited many species of flora and fauna, including a rich bird life. Many of the same waterfowl found elsewhere in Tøndermarsken are also at Nørresø Lake, but here it is possible to come much closer.


Siltoft is Denmark’s westernmost border crossing. If you turn left towards the Wadden Sea, you discover an artificial, shallow saltwater lake with a rich variety of wading birds. On the German side of the lake, the water is freshwater and therefore attracts very different species of birds.

Rudbøl Sø

Rudbøl Sø
Rudbøl Lake is quite shallow. The Danish-German border crosses through the middle of the lake. You can walk on the river dyke along the lake, where there are awesome views of the lake and its bird life. Species that breed here include the great bittern, greylag, gadwall, western marsh harrier and spotted crake. In spring, you can hear the spooky call of the great bittern here.

The great bittern is one of Denmark’s strangest birds. It is a medium-sized heron, which is difficult to spot, as it is extremely well camouflaged and very secretive. However, in spring, you can hear the male birds’ mysterious call, which sounds a little like a person blowing into an empty bottle. The great bittern’s call is loud enough to be heard over several kilometres.


Bremsbøl Sø
In 2013, Bremsbøl Lake became a Fugleværnsfonden (a Danish foundation for the protection of birds) bird sanctuary. The area was established in connection with a Danish-German project to divert water from the Vidå Stream basin to create more drainage capacity in the event of heavy rainfall. From the car park at Bremsbølvej, a path leads to a large bird hide. From the hide, there is a great view over the most part of the new lake and its artificial nesting island. Meadows with grazing cattle encircle the lake.

Bremsbøl Lake is an oasis for large flocks of wigeon, mallard and tufted ducks. Wedges of whooper and tundra swans flock here in the winter months, along with thousands of barnacle and greater white-fronted geese. The wading birds that often gather here are spotted redshanks, common greenshanks, green sandpipers and common sandpipers.