"Since the eider is the most common bird species in our archipelago, of course, this is something that people really notice. So, there's been a lot of debate about why the eider are decreasing in numbers," says Martin Green, who works with the Swedish bird monitoring program at Lund University.
Eider are migratory birds, and they've recently come back to Sweden after spending the winter in nearby Denmark and Germany. From where we're standing, we can see the inlet that eventually turns into the Baltic Sea, and that's where the archipelago is – tens of thousands of islands are sprinkled there, and so are the ducks. But they seem to be dying off. The population has fluctuated historically, but this time, the number has gone down so fast that people are worried.
"What we're talking about here is that the Swedish population has decreased from somewhere around 300-400,000 pairs to somewhere around 150,000 pairs," says Green.
Green attributes the decline to a range of factors, from disease to predation to climate change.
"I don't think there's one magic explanation," he says. But he believes the main problem is related to the food quality, and to the state of the Baltic Sea.
"Our seas are simply not in a good condition," he says, because of agricultural run-off, waste treatment and the burning of fossil fuels.
Even though the problem is still unclear, Green says that improving the water quality of the Baltic could be one solution, since that has an impact on many of the factors scientists suspect could be causing the eider population to dwindle.
The problem is not just limited to eider.
Other Swedish coastal birds are also declining and suffering, some from paralysis.
"They lose all their power in their legs and their wings and so on. The only part of the body that's still functioning is the head and the neck," says Lennart Balk, an associate professor with Stockholm University, whose research points to vitamin deficiency as a culprit.
Balk does not believe the problem is because of classical chemical pollutants. Occurences of the paralysis fluctuate widely from year to year, while the pollutants do not rise and fall in that pattern.
Balk says he is still working on finding the mechanism behind the deficiency.