This species is found in inlets and at shallow coastal waters where it rests in flocks during daytime and feed during the night and early morning. In the western Baltic Sea this species is either resting on the migration further south or wintering. They mainly feed on small fish but may also feed on small crustaceans. It is sensitive to disturbances at the resting and feeding sites.
The Red-breasted merganser is a regularly occuring migratory bird species protected under article 4.2 of the Birds Directive (Directive 2009/147/EC).