Gray seals attack eiderducks in the Baltic Sea: We have never seen that before.

Every year, Rikke Minna Hansen has had more than a handful of edderfugel nest boxes filled with eggs and chicks in her garden on Frederiksø in the Baltic Sea.

- It is a national bird here, and they are closely monitored to see when they go with their families, she says.

But this year, the edderfugel's breeding season on Christiansø and Frederiksø has not only produced small downy chicks. Gray seals, which also inhabit the islands, have developed a taste for edderfugel.

Rikke Minna Hansen has found several dead or injured edderfugel where gray seals have been active.

- They are bitten right down to the neck vertebrae and are not dead from it. Some come up on land and lie and suffer greatly. It is very disturbing to see, and I have never seen it before, she says.

Rikke Minna Hansen has had six edderfugel nest boxes in her garden this year, but has also found severely injured birds in the area for the first time. (Photo: © Marie-Louise Rafn)

When Rikke Minna Hansen finds injured edderfugel, she has called in ring marker Per Alnor Kjær, who has had to euthanize the birds. He has marked birds on Christiansø for seven years and has never experienced gray seals going after other birds like this before.

- There are no other predators in this area that can cause such damage, he says.

Since Bornholms Tidende first reported on the seal's hunt for edderfugel in April, Per Alnor Kjær has found up to 15 injured or dead edderfugel. But he estimates that there may have been more attacks.

- There were quite a few by the pier when I came in the spring. It looked like they had been flayed, if you can imagine that they had a hold of them by the legs and had a hold of the skin and pulled it off from head to toe in one long sausage.

* More of the birds that Christiansø residents have found have looked like this. Click here to see more pictures (Photo: © Charlotte Hallberg)

* More edderfugel have also been found in the water. (Photo: © Charlotte Hallberg)

1 / 2 More of the birds that Christiansø residents have found have looked like this. Click here to see more pictures (Photo: © Charlotte Hallberg) 1 / 2 More edderfugel have also been found in the water. (Photo: © Charlotte Hallberg) 2 / 2

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Edderfuglebestanden shrinks

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The edderfugel population in Denmark and the rest of Scandinavia has had it rough.

Since 2010, the population in Denmark has shrunk by 34 percent from over 22,000 breeding birds to just under 14,000 in 2020.

Researchers from Aarhus University are therefore keeping a close eye on developments.

The decline is due to several factors, according to Anders Mosbech, senior researcher at Aarhus University.

The edderfugel's food, which consists of mussels and crabs, has become scarce, and gulls, which are starving, are hovering over the eggs and nests.

Anders Mosbech is also angry that the edderfugel has ended up on the gray seal's menu.

- It's not good. It's a really bad habit from the edderfugel's perspective. It's an extra factor that contributes to the population continuing to decline.

Researchers have already begun to suspect that the seal's new feeding habits have had an impact on this year's breeding season.

Senior researcher Anders Mosbech conducts annual counts of the breeding edderfugel on Christiansø with the Christiansø Natural Scientific Field Station. This year, there has been a decline of about 10 percent compared to last year. (Photo: © Marie-Louise Rafn)

Edderfugel need to gather their strength and eat well before the hen lays on the nest for about 25 days without eating. This year, Anders Mosbech has noticed that many nests are much later in the season.

- If seals are out on the good feeding grounds and disturb edderfugel, the birds won't have eaten what they need to, and they can't get started on breeding. Either they give up breeding, lay fewer eggs, or start later, he says.

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Few seals are sinners

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While the edderfugel population in Denmark has drastically declined, the gray seal population in the Baltic Sea and the Kattegat has grown explosively.

The population was around 2,000 in 1970, but today, DTU Aqua estimates that there are between 40,000-50,000 gray seals in the Baltic Sea and the Kattegat.

Seal expert Anders Galatius from Aarhus University finds it not entirely surprising that gray seals have developed a taste for edderfugel.

- Gray seals can be quite varied. We have seen elsewhere that they can go after beaked seals, walruses, and other seabirds, but I have not heard of other places where they have gone after edderfugel, he says.

Anders Galatius believes that the gray seal's hunt for edderfugel may be due to Christiansø being a hotspot where many seals gather on very little land.

- There is a high density of seals in that area, and it means that the traditional food sources for seals are disappearing. And even though seals want to lie on land, they still want something to eat in between. And some of the seals have been resourceful.

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