Wolfgang Fiedler is an ornithologist at the Max Planck Institute for Animal Behavior in Radolfzell.

He has been researching the migratory behavior of wild birds for years - and its consequences.

Avian flu is often an issue, because the pathogen is widely spread in autumn with geese, ducks and other birds migrating from the north-east across Germany to the south.

The unusually long-lasting wave of infections last year surprised him.

He explains why there is also a spark of hope in it.

Pia Heinemann

Editor of Nature and Science

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In the summer, empty nests of gannets and dead terns have caused a stir.

Bird flu had struck.

What is the current situation?

Wild birds are quieter at the moment, there is currently no major outbreak inland.

The epidemic has also abated somewhat on the North Sea coast.

But it is estimated that thousands of seabirds have died, the outbreak was stronger than the previous worst outbreaks in 2005/2006 and 2015/2016.

And with the terns, it also affected species that had previously hardly been infected in northern Europe.

The current wave of infections overshadows everything that has gone before.

Why is that?

As with previous outbreaks, avian influenza mainly affects waterfowl, which may be due to the fact that the virus spreads well in humid environments and waterfowl tend to congregate at roosting sites in ponds and other bodies of water, especially during the migration season.

It is probably passed on via ducks that hardly ever get sick.

For reasons that are not yet clear, H5N1 did not take a summer break this year, and so it was also able to rage in breeding colonies.

In addition, it is apparently more dangerous and easier to transfer than previous variants.

Why are mallard ducks or their relatives possible vectors?

They have a very robust immune system - this may be due to the fact that they have adapted over the course of evolution to life in muddy habitats rich in bacteria and viruses.

They dig for their food and also fly long distances.

They are a good vehicle for bird flu.

Is bird flu also dangerous for songbirds?

You don't know.

It is rare to find a dead blackbird or tit.

But because most songbirds don't associate with large flocks of waterfowl and don't roost near wetlands, they tend to be more protective behaviorally.

But they are probably also strong.

Incidentally, infections from scavenging birds are known, but that is not surprising – they also eat birds that have died of bird flu, among other things.

But they hardly seem to pass the virus on.

Traditionally, migratory birds are held responsible for the spread of the pathogen in fattening and breeding poultry.

But it's not the train season at all right now, and yet chickens and turkeys have to be culled almost every day.

The Friedrich Loeffler Institute in Riems and other research institutes repeatedly analyze the chains of infection in large outbreaks on a random basis.

Sometimes it is actually the case that the entry was most likely made by a wild bird.

What if an infected duck strays into the free range area of ​​a chicken farm?

Yes.

But that rarely happens.

Despite all hygiene regulations, a poultry farmer is more likely to carry the virus into the barn himself, through dirty clothing or shoes.

The virus can also be introduced with the feed or in another way.

It has also been described that the virus was introduced into wild bird populations from the stables.

The virus does not use a one-way street.

Many birds are currently in the wintering areas in Africa or in Israel.

Are there eruptions there?

Last year there were many dead birds in the Hula Valley in Israel.

Nothing is known about this year.

Practically no monitoring is carried out in Africa, we don't know anything about that.

The bird flu had reached the island of Helgoland for the first time during the breeding season last year - and raged badly there in the gannet colony, which has around 1,300 breeding pairs.

A good 500 adult birds and many chicks perished.

Can a colony survive this?

We're hoping for immunity and that many of the birds that haven't bred in the past year—there's always some in seabirds—will fill in the gaps.

We will know more once the breeding season starts in April, May.

Do you think the virus has spread so rapidly and widely over the past year that there is general herd immunity among surviving wild birds?

Immunity is our great hope.

In the case of the gannets, it could be that the survivors are resistant and the virus has not been transmitted to the animals that have not been in contact before.

A study on this subject has already been carried out on swans on Lake Constance: In the first fall, the young animals that hatched in the summer hardly had any antibodies against harmless forms of bird flu – but older swans did.

This means that every swan will come into contact with the flu virus during its lifetime.

If these influenza variants are harmless, the bird can develop an immunity that then protects it from more dangerous variants.

Many waterfowl should therefore always be prepared.