From polder to pole, the extraordinary journey of the barnacle goose

Category: MBP newsletter content

Published: July 28th, 2023

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The picture of winter in Oostvaardersplassen is dominated by some 40,000 barnacle geese. The black and white geese are quite striking on the green grasslands, and their plumage hints at a very different landscape. Having eaten their fill, they will soon leave for the rocky cliffs of Nova Zembla and the Russian tundra. Why do they fly 3,000 kilometres from the polder to the pole, and how is their journey affected by climate change? Researcher Michiel Boom has been seeking answers to these questions for six years.

Barnacle geese on the grasslands of Oostvaardersplassen in May
Barnacle geese on the grasslands of Oostvaardersplassen in May

"The barnacle goose is doing well!", says Michiel Boom, researcher at the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam. If you look on the grasslands of Oostvaardersplassen in winter, you would come to the same conclusion, you can no longer see the grass because of the geese. Whereas in 1960 there were only 20,000 in the Netherlands and Germany, now there are 1.2 million. Since 1991, they have found Oostvaardersplassen as a wintering habitat. Here, some 40,000 barnacle geese can now feast on fresh, protein-rich grass. With their small beaks, they are especially good at eating the short, young tips, which are also the most nutritious. The large grazers help them keep the area short, so they don't lack anything here. Michiel shows the movements of three tagged barnacle geese on a map.

"You can see that the barnacle geese are moving through the area, where in January and February they still mostly stay on the northern parts of the grasslands, around March April they move more towards the south." "Then they follow the movement of the large grazers," replies Tjibbe Hunink, ecology forester. "Particularly with the red deer, it is noticeable that as spring arrives, they also move more towards the south of Oostvaardersplassen." Also, at the beginning of the year, the geese still commute between Oostvaardersplassen and (agricultural) grasslands in the Netherlands, when the grass grows fully in Oostvaardersplassen from April onwards, they stay in the area all day to forage.

Movements of barnacle geese by month. Dark blue/purple = January - February, light blue/cyan= March - May (Map by Michiel Boom)
Movements of barnacle geese by month. Dark blue/purple = January - February, light blue/cyan= March - May (Map by Michiel Boom)

Barnacle geese leave for their breeding grounds around mid-May, but used to leave around mid-April. "Earlier, they still often stopped at the Baltic Sea, but there are now breeding populations there too, so there may be too much competition. The geese are now building up more reserves in the Netherlands because they are short of a road stop along the way. The food-rich grass in the Netherlands helps them do this. The geese almost double in weight before they leave to make the journey of over 3,000 kilometres without too many stops. I now see some barnacle geese struggling to get off the ground because of their weight," Michiel says. Along the way, barnacle geese now find out in some years that it is already much warmer than they expected. Due to climate change, the poles in particular are warming up quickly, something they have not yet realised in the Netherlands. Suddenly, they then have to hurry, sometimes making this journey in a week.

Barnacle goose on nest of downy feathers on the Russian tundra (Photo by Michiel Boom)
Barnacle goose on nest of downy feathers on the Russian tundra (Photo by Michiel Boom)

They try to time the moment of departure so that they arrive at Nova Zembla before the snow is melting there. "That's probably why they originally breed high up on the cliffs, those are the first places that are free of snow and predators have difficulty getting there." Nesting material is not available in this rocky area. They therefore make their nest from their own down feathers. They pluck these from their bellies, creating bare skin there. The body heat is thus optimally used for incubating the eggs, and the down feathers provide insulation around the eggs. What an ingenuity... When the eggs hatch after 26 days of incubation, the grass has just started to grow, and has optimal food richness for the young geese to quickly fatten up. But, how do they get to that succulent grass? They can see it from their nest but that is a huge precipice, and the young can't fly yet. It is bizarre but true, the youngsters drop off the cliff, and often survive this leap of faith too.

Arctic fox on the Russian tundra (photo by Michiel Boom)
Arctic fox on the Russian tundra (photo by Michiel Boom)

Some geese pods have a somewhat less adventurous start to their lives these days. As the pole warms, barnacle geese no longer have to breed only on the cliffs. Rather, the tundra is becoming snow-free, giving them a large breeding area. But there another danger lurks...For among the brown/green vegetation, the black and white geese are not camouflaged. On the ground, the nests are also more easily accessible to predators such as the Arctic fox, in addition to the bald eagle, the Heuglins gull and the lesser skua. These target the eggs, and later, the easily outsmarted chicks. Not only that, on the mainland the brown bears are approaching and the polar bears are staying behind on the breeding grounds on Svalbard as the sea ice retreats earlier, preventing them from heading north. With that, the barnacle goose has added a pair of predators.

Barnacle geese leave for their arctic breeding grounds again around this time

Despite all these hardships, it seems for now that the changes are working out well for the barnacle goose. The goose follows its food, and therefore maintains a flexible attitude to life. Barnacle geese are now leaving Oostvaardersplassen. Knowing what they have to go through to stay alive and pass on life to the next generation, I now look at this beautiful goose very differently. Full of awe I wave them off, and with great wonder and joy I will welcome them back to Oostvaardersplassen in October.

Author: Forester Rosan op den Kelder in Oostvaardersplassen

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