Visions from nature

Norway’s New Invaders: The Greater Canada Goose

By Sam Perrin

We kick off our series of articles on Norway’s new invaders this week with the greater Canada goose. My association with these creatures is one of mild terror, having had to dodge them on campus during my time in Canada. But in Norway, and all across Europe, they’ve been a huge economic problem for decades, and are listed as one of only four birds on the EU commissioned list of Europe’s 100 worst invasive species.

What are they?

Branta canadensis, the greater Canada goose, has the most damaging impact of all alien bird species in Europe. They have already reached most of their potential habitat here in Europe, and occupy most of Scandinavia, having first been introduced to Norway in 1936. Their native populations breed in the tundra across North America every year, migrating south to Mexico and the US in winter, and can cover almost 2400km in a day while riding with the wind. They are enormous, with a wingspan of up to 185cm, and having spent 3 months in Canada dodging them, I can also attest to the fact that they are not shy of people, incredibly aggressive and worth avoiding whenever possible.

Here you can see two Canada geese, plotting crop destruction and probably also manslaughter
Here you can see two Canada geese, plotting crop destruction and probably also manslaughter (Photo Credit: Wikipedia Commons)

How did they get here?

The goose was first introduced to Europe in the 1930s, for a number of reasons. In some countries it was first introduced to increase local biodiversity, in others it escaped from local zoos. However in Norway, as in many other countries, it was introduced for hunting purposes. Whilst initial introductions didn’t make much of an impact, in the 60s and 70s just under 1,000 geese were introduced to the south of Norway, and this, combined with similar introductions in southern Sweden, mean that the two countries today have the highest populations of the species in Europe.

What do they do?

The worst and most obvious impacts that the geese have are destruction of crops and vegetation, which have a huge impact economically and aesthetically. Goose trampling can also lead to soil compaction, which decreases the chances of regrowth. Combined with the significant levels of bird droppings, this crop destruction leads to substantial eutrophication of freshwater networks in Norway. The birds also spread several diseases and parasites, including avian flu and salmonella, which can infect humans and native fauna alike. The fact that they thrive in human areas mean they can also prove a physical threat, as well as the issues they present to the aviation industry, with over 120 aircraft lost due to bird strikes since 1990. Remember that movie Sully in 2016? That’s right, they were the villain in a Tom Hanks movie.

How do we stop them?

The introduction of hunting licenses for invasive species is often a problematic issue, with debate over how effective a method of population control it is. The US government has proposed constructing a wall on their border with Mexico to prevent them from returning to the US after winter, however this is expected to be prohibited by cost and sanity. Yet the population does need to be managed, and the introduction of Canadian geese into Norwegian hunting culture could at least raise awareness of the problem. A study last year in Belgium showed that targeted captures of geese while they are molting (during July), can reduce damage costs accrued by the geese by between 21 and 45 million euros.

For more information on the geese, we invite you to read the following studies.

Canada Geese in Living with Wildlife, by the Washington Department of Fish & Wildlife

Cost-benefit analysis for invasive species control: the case of greater Canada goose Branta canadensis in Flanders (northern Belgium) by Nikolaas Reyns et al.

Invasive Alien Species Fact SheetBranta canadensis by the Online Database of the North European and Baltic Network on Invasive Alien Species


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