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Location Denmark, Sønderjyllands Amtskommune
Central coordinates 8o 43.00' East  54o 54.00' North
IBA criteria A4i, A4iii, B1i, B2, B3, C2, C3, C4, C6
Area 6,520 ha
Altitude 0 - 10m
Year of IBA assessment 2000

Dansk Ornitologisk Forening

Site description A large area of reclaimed land with meadows along the Vidåen river. In the western part a saltwater lagoon is maintained by pumping in seawater. The inner (eastern) parts are mainly agricultural and the outer (western) parts predominantly pasture. There is also some standing freshwater, notably Rudbøl Sø, and reedbeds.

Key Biodiversity This is a very important staging area for several waterbirds, with total numbers exceeding 20,000 individuals. Several species listed on Annex I of the EC Birds Directive breed at the site, including Botaurus stellaris, Ciconia ciconia, Circus aeruginosus, Circus pygargus, Porzana porzana, Recurvirostra avosetta, Sterna hirundo, S. paradisaea, S. albifrons, Chlidonias niger (the most important site in Denmark for this species) and Luscinia svevica.

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
Northern Pintail Anas acuta non-breeding  1994  900 individuals  good  B1i, C3  Least Concern 
Barnacle Goose Branta leucopsis non-breeding  1997  30,000 individuals  good  A4i, B1i, C2, C6  Least Concern 
Brent Goose Branta bernicla non-breeding  1994  6,800 individuals  good  A4i, B1i, C3  Least Concern 
Whooper Swan Cygnus cygnus non-breeding  1994  941 individuals  good  A4i, B1i, C2  Least Concern 
Tundra Swan Cygnus columbianus non-breeding  1993  332 individuals  good  A4i, B1i, B2, C2  Least Concern 
Common Shelduck Tadorna tadorna non-breeding  1994  6,500 individuals  good  A4i, B1i, C3  Least Concern 
Pied Avocet Recurvirostra avosetta breeding  1994  248-482 breeding pairs  good  B1i, B3, C2  Least Concern 
Pied Avocet Recurvirostra avosetta passage  1994  1,300 individuals  good  A4i, B1i, C2  Least Concern 
Eurasian Golden Plover Pluvialis apricaria passage  1994  25,000 individuals  A4i, B1i, C2  Least Concern 
Black-tailed Godwit Limosa limosa breeding  1994  110-125 breeding pairs  good  B2  Near Threatened 
Bar-tailed Godwit Limosa lapponica passage  1994  4,600 individuals  good  A4i, B1i, C2  Near Threatened 
Spotted Redshank Tringa erythropus passage  1994  1,270 individuals  good  A4i, B1i, C3  Least Concern 
Red Knot Calidris canutus passage  1994  21,300 individuals  good  A4i, B1i, C3  Near Threatened 
Dunlin Calidris alpina passage  1994  62,000 individuals  good  A4i, B1i, C3  Least Concern 
Black Tern Chlidonias niger breeding  1994  36-41 breeding pairs  good  C2, C6  Least Concern 
A4iii Species group - waterbirds non-breeding  20,000-49,999 individuals  unknown  A4iii, C4   
A4iii Species group - waterbirds passage  1994  100,000-499,999 individuals  unknown  A4iii, C4   

IBA Monitoring

2010 not assessed very unfavourable not assessed
Good - based on reliable and complete / representative data

Anser anser Greylag Goose 6700 6000 individuals 90 near favourable
Charadrius alexandrinus 23 5 individuals 22 very unfavourable
Pluvialis squatarola Grey Plover 3600 2100 individuals 59 unfavourable
Limosa limosa Black-tailed Godwit 242 101 breeding pairs 42 unfavourable
Calidris alpina Dunlin 9 0 breeding pairs 0 very unfavourable
Calidris pugnax Ruff 87 0 breeding pairs 0 very unfavourable
Sterna paradisaea Arctic Tern 133 13 breeding pairs 10 very unfavourable
Sternula albifrons Little Tern 12 1 breeding pairs 9 very unfavourable
Asio flammeus Short-eared Owl 2 0 individuals 0 very unfavourable
Luscinia svecica Bluethroat 50 50 breeding pairs 100 favourable

Protected areas

Protected area Designation Area (ha) Relationship with IBA Overlap with IBA (ha)  
Kiers Gård Margrethe Kog Protected by Conservation Order 2 protected area contained by site 2  
Margrethe Kog Protected by Conservation Order 1,320 protected area contained by site 1,245  
Tondermarsken Statsfredning Protected by Conservation Order 2,490 protected area contained by site 2,490  
Vadehavet (Wadden Sea) Wetlands of International Importance (Ramsar) 150,482 protected area contains site 6,520  


IUCN habitat Habitat detail Extent (% of site)
Coastline Lagoons; Salt marshes  30%
Artificial - terrestrial   70%

Land use

Land-use Extent (% of site)
nature conservation and research 15%
agriculture 85%

Protection status National Partial International High6,520 ha of IBA covered by Special Protection Area (Vidåen, Tøndermarsken and Saltvandsøen, 6,520 ha).

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Recommended citation  BirdLife International (2016) Important Bird and Biodiversity Area factsheet: Tøndermarsken, Magisterkog and Rudbøl Sø. Downloaded from on 24/10/2016

To provide new information to update this factsheet or to correct any errors, please email BirdLife