Sømosen is situated west of the suburb of Herlev, next to Lautrupparken. The green area, of which one third is a park with grass and scattered bushes, is neighbour to many large institutions and popular for a short walk in the open air. The bog itself was formed in a hollow after the last Ice Age. It is drained by the stream of Sømose Å. The bog was previously very overgrown, but during the 1980’s the municipality of Ballerup carried out an extensive re-establishment project, opening up large stretches of water and recreating islands and islets where birds can breed without being disturbed. Sømosen has developed into a little oasis with a rich birdlife. In addition to the large colony of Black-headed Gull, three species of grebe breed here ( Little Grebe, Great Crested Grebe and Red-necked Grebe), together with many waterfowl. Waders include Northern Lapwing and Little Ringed Plover. Common Tern breed here and can be seen foraging throughout the summer. Passerines include Cuckoo, Thrush Nightingale and many warblers. The biggest attraction for birdwatchers is probably breeding Penduline Tit. However, the tits have unfortunately not nested here the last few years, although they can sometimes be spotted in the area in spring.
Sømosen is also an excellent locality for migrating and staging birds both spring and autumn. Geese, ducks ( Garganey , Common Teal , Northern Pintail , Eurasian Wigeon , Gadwall and Northern Shoveler ) can be observed. Raptors include a fair number of Common Buzzard and smaller numbers of European Honey-buzzard, together with infrequent visitors such as Red Kite, Rough-legged Buzzard, White-tailed Eagle, Hen Harrier, Marsh Harrier, Osprey (often seen foraging) – and with some luck Merlin and Peregrine Falcon. Great Bittern has been observed on a few occasions. If there are easterly winds flocks of Common Crane may appear. Many waders ( Eurasian Oystercatcher , Northern Lapwing , Little Ringed Plover , Common Greenshank , Green Sandpiper , Wood Sandpiper , Common Sandpiper, Snipe og af og til Woodcock ).
In addition, Lesser Black-backed Gull and Great Black-backed Gull and even Caspian Tern are occasionally seen. Also sparrows, a lot of larks, pipers, wagtails, swallows, thrushes and finches rest and pull in and over the bog. Bearded Tit is seen occasionally. Common Redstart , Whinchat, Northern Wheatear, Spotted Flycatcher, Pied Flycatcher, Red-backed Shrike and Common Redpoll and Lesser Redpoll are seen regularly. Great Reed Warbler has visited the bog for a single year.
In the winter months many wildfowl can be seen and visitors from northern Scandinavia may turn up: Whooper Swan, Taiga Bean-Goose and Canada Goose. In periods of frost, one may be lucky enough to see Water Rail foraging at close range in Sømose Å or even a Jack Snipe. In some years there can be invasions of Fieldfare, Redwing or Bohemian Waxwing, and many colourful finches.
If using public transport, Sømosen is most easily reached from Copenhagen by taking bus 350S and getting off at Københavns Teknikum (the Copenhagen University College of Engineering) in Ballerup. One can also take the local 167/168 bus from Herlev Station (get off at Herlev Stadium and walk down Rørløkken to Sømosen). If coming by car, it is possible to park on Vingekrogen. There is a bird observation tower in the south-east corner of the bog, and in the north-east corner is a jetty which is very useful as a look-out post.