Tagging seabirds with transmitters is a particularly useful method for gaining greater insight into the seabirds’ behaviour and habits – both for the biologists who are carrying out the environmental surveys and for people in general. 

Before the birds can be tagged, they have to be caught. This is best done with nets at night, a difficult exercise that requires both patience and experience. The radio/satellite transmitters then enable the seabirds’often long and exciting flight paths to be charted. 

Eider pairings
The Eider is one of the species of seabirds whose private life is studied carefully. The Fehmarnbelt is one of the eider’s wintering areas and eider males tend to arrive in the area from their summer holidays at the Wadden Sea during August to October. Here, they choose one of the females before forming a pair bond.

The mating takes place in the winter habitat. After mating – typically at the end of March – the pair head northwards. After a day or two in flight, they settle on the still frozen sea between Finland and Sweden while waiting for the ice to melt in order for the female to lay her eggs on one of the area’s small islands where the eggs are safe from foxes, raccoon dogs, etc.

Around the bridges
Eider migration is just one of the many aspects of the life of seabirds, which is carefully monitored by the birds experts conducting the environmental surveys.

Another element is the birds’ behaviour around bridges, which is being recorded in the event that a bridge is chosen as the preferred solution. Consequently, comparative studies have been carried out at, for instance, the Kalmarsund Bridge, which links the Swedish mainland with Öland.

Tagging with transmitters provides biologists with information about the seabirds’ flight paths around bridges and can, therefore, be useful for the Fehmarnbelt link project. The method can also help identify other exciting aspects of the life of seabirds and their habits.