A requiem for birds killed by alien predators

A small pond in the Finnish countryside is filled with squeaking, when several goldeneye (Bucephala clangula) and wigeon (Mareca penelope) broods are foraging. Suddenly a goldeneye hen alerts and flies cackling across the pond. The figure of an American mink (Neovison vison) appears on the water surface, which leads to an emergency escape of the duck broods. The American mink is an efficient predator, which does not belong in Finnish nature. Nonetheless it has already occupied the whole country. Alien species in Finland and other countries are a serious threat to birds.

Wetland ecology group_University of Helsinki_duck_goldeneye_wigeon_wetland

Duck broods escape after a watchful goldeneye female alerts after spotting an American mink.

A fur farming runaway became a nuisance

The American mink is, as its name reveals, an American species, which was brought to North Europe at the beginning of the 20th century. Minks escaped from farms and were successful in Europe. They were also introduced to nature on the Russian side. Rapidly American minks occupied all of Fennoscandia.

The American mink utilizes various wetlands, lakes and archipelagos, where it predates birds and limits their populations. Minks don’t only eat birds, but also their eggs. The American mink is especially harmful in Fennoscandian archipelagos, because birds are not adapted to such predators. Certain bird species, such as the black guillemot (Cepphus grylle), are especially threatened by mink predation. Traditionally Fennoscandia has not had such predators. The European mink (Mustela lutreola), which is now extinct from many of its historical areas, did not occupy the archipelago in the same way as its American cousin does.

Wetland ecology group_University of Helsinki_American mink_alien predator_wetland

The American mink is currently a common wetland species in Fennoscandia.

Raccoon dog ended up on EU’s black list

The raccoon dog (Nyctereutes procyonoides) is an Asian species that was introduced to the European parts of the Soviet Union to be hunted for its fur. From the Soviet the raccoon dogs spread west. Soon raccoon dogs occupied all of Finland, and are now also reaching Sweden. Currently Finnish hunters are working to prevent raccoon dogs from going over the Swedish border. The raccoon dog was recently classified as an invasive alien species by the European Union. One reason for this is its influence on birds.

Wetland ecology group_University of Helsinki_supikoira_raccoon dog_vieraslaji

Raccoon dog destroys an artificial duck nest. Game camera photo.

Research conducted at the Helsinki University shows that raccoon dog density and predation pressure on artificial nests correlates on wetlands. Other studies have found raccoon dogs to destroy both pheasant and duck nests. Thus raccoon dog removal around wetlands is an important way to protect birds.

And then there were no Stephens Island wrens left

A cat named Tibbles carried little birds to a light house yard on an island of New Zealand in the late 1800s. The birds were Stephens Island wrens (Xenicus lyalli). The cat hunted at least 15, after which apparently none were left. Rats and cats might already have killed the wren populations from the other islands. The Stephens Island wren is not the only victim of cats. Australian researchers have counted that domestic cats have killed at least 20 native species. In the USA cats are estimated to kill 3,7 milliard (3.7 billion) birds annually. Most birds are killed by unowned cats. Cats therefore appear to kill more birds than any other anthropogenic cause in the USA. Worldwide cats have killed 33 animal species to extinction.

Wetland ecology group_University of Helsinki_cat_alien predator_wetland

A cat stalking a duck brood in a wetland. In this case cutting the vegetation saved the brood.

The raccoon is occupying Europe

In addition to the American mink, the raccoon (Procyon lotor) has also arrived in Europe from North America. The raccoon was also brought Europe to be farmed for its fur. This highly adaptable animal has succeeded well in Europe, and is now common for example in Germany and France. The population size in Germany is already evaluated at over a million. Raccoons are spreading north, and are currently settled in Denmark and individuals have also been found in Sweden. Compared to raccoon dogs, raccoons also live successfully in cities. But just like raccoon dogs, raccoons are also well adapted to the wetland environment, and are thus harmful to waterbirds.

Raccoons reproduce effectively, and therefore their extirpation is impossible once a population has been established. This is why efforts need to be focused on stopping the species from spreading. The raccoon is classified as an invasive alien species in the EU, so farming them or having one as a pet is illegal.

Read more:

Väänänen, V.-M. 2007: The effect of raccoon dog Nyctereutes procyonoides removal on waterbird breeding success. Suomen Riista (PDF)

PHYS.ORG 29.1. 2014: Cats in US kill billions of birds, mammals, study finds

Loss, S.R. et al. 2013: The impact of free-ranging domestic cats on wildlife of the United States. Nature Communications

Marra, P. & Santella C. 2017. Cat Wars. The Obituary of the Stephens Island Wren

Spiegel Online 3.8.2012. Germany Overrun by Hordes of Masked Omnivores

NOBANIS Invasive Alien fact sheets, Raccoon (PDF)

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