Many Dutch carp moved to bigger lake

This October 2018 Dutch video is about Oostvaardersplassen national park in the Netherlands.

This is a marshy area, a good environment for, eg, white-tailed eagles and reed warbler relative birds.

However, now the water level is too high. Reed beds disappear. Bad for reed warblers, bluethroats and similar birds.

So, the video says, there are plans to make the water level 80 centimetre lower. But that would mean not enough water for the many carp living there now.

This 2019 video is about spawning carp in the Oostvaardersplassen nature reserve in the Netherlands.

Jonathan van Deelen made this video.

Today, ranger Hans-Erik Kuypers blogs about these carp.

Ever since November 2019, 38 tons of carp have been caught and moved to the much bigger Markermeer lake next door, so that the fish that will stay in Oostvaardersplassen will have enough space as the water level drops.

The carp moved to the Markermeer weigh on average five kilograms and are 70 centimetres long. They are healthy. Some of them were freed in the Markermeer with radio transmitters on. The transmitter data showed the fish stayed in the Markermeer. So, there was enough food for them.

More carp will be moved until 2021. And then, the lower water level should provide a good environment for reed beds, reed bed birds and the fish that were not moved.

Barn swallows, parasites and evolution

This September 2016 video is about a barn swallow nesting colony in a hide in the Oostvaardersplassen national park in the Netherlands.

From the University of Colorado at Boulder in the USA:

Resident parasites influence appearance, evolution of barn swallows

June 24, 2020

Summary: Researchers think that local parasites are influencing why barn swallows in Europe, the Middle East and Colorado are choosing their mates differently. Their new research finds that these parasites could be playing an important role in changing the traits displayed to attract mates early in the process of the creation of new species.

Barn swallows live almost everywhere on the planet, recognizable by their forked tail and agility in the air. Yet while they share these characteristics, these little birds often look slightly different in each place they live — with some so distinct they’re splitting off to become new species.

Researchers at CU Boulder think that local parasites are influencing why barn swallows in Europe, the Middle East and Colorado are choosing their mates differently. Their new research, published in Evolution, finds that these parasites could be playing an important role in changing the traits displayed to attract mates early in the process of the creation of new species.

“It’s possible we haven’t appreciated just how important parasites might be in shaping the evolution of their hosts,” said lead author Amanda Hund, who conducted the research as a doctoral candidate in the Ecology and Evolutionary Biology Department.

Every organism, including humans, has co-evolved with a unique community of parasites, that by definition live at the expense of their host. While they are not beneficial to us like many other microbes are, parasites have shaped our own immune system, pheromones and even our mate selection, previous research has shown.

Hund set out to characterize as many parasite communities as she could in barn swallows, to find out if they could be influencing their mate selection, and therefore the male birds’ physical traits and the creation of new species.

Hund and her colleagues studied barn swallows at sites in Colorado, the Czech Republic and Israel over four years. They measured the number and types of parasites on them, in their nests and in their blood and tracked who they chose to mate with in a given breeding season, their sexual signals — breast color, throat color and tail shape — and their health and the survival rate of their offspring.

In all but one population in the study, the most “attractive” males had fewer parasites. Somehow the male birds’ breast color, throat color and tail shape allowed females to make informed choices about their health and the likelihood of reproductive success with that partner.

Many birds also had multiple parasites with connections to the same physical trait. For example, in Colorado, males with darker breast color are less likely to have mites, but more likely to have malaria. Nest mites are detrimental to the nestlings’ survival — whereas malaria only impacts the male bird.

“Males are investing in traits to attract females, and it looks like that comes at a cost — where they are more attractive, but also more susceptible to malaria,” said Hund, now a postdoctoral fellow at the University of Minnesota. “It is a tradeoff.”

Evolution in action

Researchers who study the origin of biodiversity, or why the Earth has so many different species, often examine which traits animals are choosing in their partners. But the real question is: Why are they choosing those specific combinations of traits?

To answer that question requires a very detailed type of scientific research, looking at the full reproductive cycle, health and survival rate of a population, in order to create a rich data set that unpacks how evolution is working between closely related populations.

“Most people are really good at characterizing the pattern. But Amanda’s work is very special in terms of trying to unpack the process,” said Rebecca Safran, associate professor in the Department of Ecology and Evolutionary Biology and co-author on the study.

Many factors affect the divergent evolution of species. But as opposed to something like the weather, parasites are evolving as rapidly as their host species — leading to a co-evolutionary relationship. While this has been studied in other animals, it has only previously been studied in one barn swallow population in Europe.

Barn swallows make a great study specimen: they’re ubiquitous and charismatic.

“These birds have evolved alongside humans for thousands of years. Every culture that we’ve visited seems to have its own unique story or relationship with this bird,” said Safran.

But because they nest almost exclusively in human-made structures — barns, bridges, culverts and the like — barn swallows often live on private land. It turns out that winning the trust of landowners is as much a part of the work as catching the birds.

“Public relations is a very large part of barn swallow research,” said Hund.

Safran has been working with dozens of collaborators all over the world for over a decade. Hund built off these connections to do this research in Europe and the Middle East, facing unique circumstances and language barriers along the way.

In Israel Hund lived on a Kibbutz, a collective community, in order to complete her research over several months. In the Czech Republic, Hund used award-winning skills from her childhood and rode horses at an equestrian center to build trust and gain access to an important nesting site.

And here in Colorado, there were landowners who were unsure or suspicious of the project at the start of the breeding season. “But by the end, they were having us over for dinner,” said Hund.

The work doesn’t stop here. The researchers are already trying to answer the next big question: why are local parasites and certain sexual traits linked?

“And once you really figure that out, you can export that knowledge and our study methods to other populations and actually watch mate selection decisions and the associated reproductive consequences unfold,” said Safran. “It’s like watching evolution in action.”

Female eaglet ringed in Oostvaardersplassen national park

This 8 June 2020 video shows the ringing of a female white-tailed eaglet in Oostvaardersplassen national park in the Netherlands.

Warden Tjibbe Hunink reports today that the young bird got two rings: one orange, one black. Her name is now WN21.

Her parents had provided her with food of at least these four species: carp, grey lag goose, teal and coot.

Young sea eagles hatched in Oostvaardersplassen

This 8 April 2020 video shows a sea eagle nest in Oostvaardersplassen national park in the Netherlands.

You can hear Cetti’s warbler, chiffchaff and greylag goose sounds.

Warden Hans-Erik Kuypers reports that on 8 April, it was discovered that eaglets had hatched at that nest.

From 2006 on, sea eagles have nested successfully in Oostvaardersplassen year after year, except for 2019.

In 2019, 15 white-tailed eagle couples nested in the Netherlands.