The nature reserve was established by Norrtälje municipality in 2002. The purpose of the reserve is to preserve the forest and rocky marsh area with its plant and animal life and geoscientific phenomena that are very valuable from a research, nature study and outdoor recreation point of view. 

The area is a classic observation site for birds. A total of 219 bird species have been recorded at Rönnskärs udde. Today, an estimated thousand people visit the area annually. The area covers 2.3 hectares.2.3 hectares, of which 1.5 hectares is a forest stand and the remaining 0.8 hectares of rocky outcrops facing the sea.

Fault and ice shelves
Rönnskärs udde is located on the edge of the regional fault in the bedrock that has formed the distinctive dividing line between land and sea along the outside of Väddö. A short distance off Rönnskär's headland, the sea depths soon reach 30 metres. On the glacial outcrops on Rönnskär's headland, there are ice grooves formed during different ages.

Unimpacted forest land
The woodland on Rönnskärs udde is unaffected by various types of exploitation and no forestry measures have been taken in recent decades. The forest was affected by the storm Alfrida in 2019 and the trees that fell have been left behind, but the paths have been cut. The forest is dominated by spruce with elements of aspen, pine and birch. The woodland contains the orchid knotweed, a species associated with older coniferous forests.

The 1.5 hectare forest stand is not protected by the Rönnskärs udde reserve decision. Since 19 December 2001, the stand has been protected as a biotope conservation area by the Mälardalen Forestry Agency. The aim of the reserve is to allow the vegetation to develop freely without management measures. Trees and shrubs, both living and dead, are to be left untouched. Small management measures to favour red-listed species may need to be implemented in the long term.

Classic bird room
The rocky area at the far end of Rönnskär's headland is a classic observation site for migratory birds. It is during autumn that bird migration is at its most intense. Rönnskärs udde is one of the easternmost landmarks along the entire Väddökusten coast and is an important area for heavily fatigued small birds that have managed to cross the Åland Sea.

At the end of September and October, the southbound migration is at its most intense, with loons, lapwings and eiders. A visit in November or December brings some lingering seabirds of several species. In ice-free winters there may be, for example, little auks, cormorants and long-tailed ducks on the coast. The spring migration past Rönnskär's headland begins as early as March with eiders, goldeneyes, lapwings and curlews. At the turn of April, lapwings, wood pigeons and ringed pigeons, skylarks and many other species pass by. 

Nature type: coast, sea and archipelago, forest
Available here: parking, paths, fireplace

Find your way here!
Rönnskärs udde nature reserve is located about 25 km northeast of Norrtälje and about 5 kilometres east of Älmsta. The easiest way to get here is by road from Älmsta via Hammarby and Sandviken to Rönnskärs udde. From the south-west corner of the nature reserve by the gravel road, a small but well-trodden path leads down to the sea. The path is about 200 metres long and splits into two paths, with the northern one ending at the most used bird observation site.