Travel Report: Marinde Out, Netherlands

May 09, 2014

Marinde Out, a Doctoral student in Biology, received a Graduate International Research Travel Award to further her research in the Netherlands. Her report:

Predators have strong influences on the whereabouts of their prey. Without top predators, there are no limits where and when prey can forage. Can predator-prey interactions play a role in conservation plans? This is what I want to find out by studying the interactions between expanding sea eagle populations and migratory geese.

It was easy to feel like a goose when I flew from Vancouver to Amsterdam on the 21st of April to do ecological fieldwork for my Ph. D. project. Leaving a place where spring had already started, cherry blossoms in full bloom. Descending in a place where tree buds just started to escape from winter’s frost. That is what geese do on spring migration: they follow the growth of fresh spring grass. While following growth of grass was part of my mission, I was also looking for something more majestic.

The geese I am talking about are beautiful Palaearctic black and white grass-eating birds, called barnacle geese (Branta leucopsis) which now stay one month longer in their wintering habitat (the Netherlands) than they used to before the mid 1990s. This change in migration behavior is a nuisance for Dutch farmers who earn money with grass, because the longer geese stay, the more damage they cause. Additionally, barnacle geese were rare in the 1960s, but their population has now reached more than a million birds.

Why are geese departing later? Does it have something to do with food availability, or is there another explanation looming from above? My goal was to tackle these questions.

The geese I study migrate from the Netherlands to breed in Northern Russia, but in between they stop to refuel on coastal grasslands of the Baltic coast (Sweden and Estonia). Less food has become available than before the 1990s in the Baltic because many grasslands that used to be grazed by cattle have slowly become overgrown by shrubs. The explanation looming from above is the recovery of the white-tailed sea eagle (Haliaeetus albicilla), a barnacle goose’s archenemy. These majestic raptors went almost extinct in the 1970s due to the detrimental effects of DDT. The majority of eagles can be found around the Baltic Sea, while only a few breed in the Netherlands where barnacle geese winter. The increased danger in the Baltic could be the reason why geese stay longer in the Netherlands.

With financial aid from the Graduate International Travel Award, I had the opportunity to study barnacle geese both on their wintering grounds in the Netherlands and on their stopover site on the Baltic coast of Estonia. By observing how and where they grazed, I wanted to find out if danger was driving them, or food shortage. Measuring, cutting and drying grass, counting faeces, and observing geese and eagles were part of the job. Finding field assistants first seemed challenging but I couldn’t have better ones. My father Nico Out combed through the Dutch salt marsh to help with data collection. After my Estonian colleague Tarvo Valker showed me the best barnacle goose havens, my assistant David Knuvelder joined the Estonian adventure and quickly gained new abilities like walking through hazardous mosquito clouds without complaining. We did not expect to experience a heat wave with daytime temperatures of 30ºC in early May. Rain clouds were welcomed and cheered upon because they made the bugs disappear, and we learned to enjoy crossing marshes in our new rubber boots.

In the stunning Estonian nature we frequently saw the phenomenon that I ended up calling a goose bomb, when huge clouds of thousands of geese exploded as they responded to an eagle flying over. Eagles definitely scare the faeces out of the geese, so to speak. However, I need more information to find out if they are the real cause of the delay in migration. On the 14th of March I presented part of this work at the Changing World of the Geese Symposium in Wageningen, the Netherlands. Currently I am already collecting more data in the Netherlands, taking advantage of the lessons I learned last year. In May I return to Estonia to conduct more detailed observations and to get a better grasp on the system. I am honoured to gain all these extraordinary experiences, which would not be possible without the support of my supervisor Prof. Dr. Ron Ydenberg.

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Tags: Student Voices; Biology

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