Tag Archives: bird

Quantifying the Effect of an Invader

The Raccoon Dog, an alien species, has made its way to Sweden recently. But what sort of effect does it have on the native fauna?

The Raccoon Dog, an alien species, has made its way to Sweden recently. But what sort of effect does it have on the native fauna? (Image Credit: Prue Simmons, CC BY 2.0)

Nest predation by raccoon dog Nyctereutes procyonoides in the archipelago of Northern Sweden (2018) Dahl & Åhlen, Biological Invasions, https://doi.org/10.1007/s10530-018-1855-4

The Crux

We’ve spoken about biological invasions at length on EcolMass, and the detrimental effects that the arrival of a new species can have on native populations. Yet eradication is often impossible, and management expensive, so before taking extensive action, it’s always important to ensure that an alien species IS having a negative effect.

The raccoon dog is an Asian species, closely related to foxes, that was introduced to Europe in the early 20th century and has since spread into Scandinavia. Voracious predators that could spread further north due to climate change, our paper this week looks at the extent of their impact on the ecosystems they’ve spread to.

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Biological Annihilation

The sumatran orangutan, one of many species facing extinction in the earth's sixth mass extinction event

The sumatran orangutan, one of many species facing extinction in the earth’s sixth mass extinction event (Image Credit: Mike Pennington, CC BY SA 2.0)

Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines (2017) Ceballos et al., Proceedings of the National Academy of Sciences of the USA, DOI: https://doi.org/10.1073/pnas.1704949114

Guest Post by Jonatan Marquez

The Crux

The rate at which species and populations have been going extinct in the last couple of centuries has well and truly earned the title of the planet’s sixth mass extinction event. However, most people rarely realize the severity of the situation. Hearing about the loss of two vertebrate species a year or having the last of some far-off species die out doesn’t see to cause much concern in the general public.

A species extinction is always preceded by population declines and extinctions. Perhaps highlighting the state of natural communities at this level might put the severity of the situation in better context. For example, the Living Planet Index (LPI) estimates that between 1970 and 2012, wildlife abundance has decreased by 58%. This paper focuses on the state and trends of populations of vertebrates by analysing i) the proportion undergoing declines or shrinkages, ii) the global distribution of population reduction events and iii) the general scale of population declines among mammal populations.

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The American Mink

The American Mink is pretty much a Norwegian mainstay these days. So what sort of impact have they had?

The American Mink is pretty much a Norwegian mainstay these days. So what sort of impact have they had? (Image Credit: Ryzhkov Sergey, CC BY-SA 4.0)

Fur farming isn’t a topic we’ve had much cause to touch on so far in this series. But today, we look at a species that was introduced specifically for that purpose, whose presence in Europe is disliked by ecologists and animal rights activists alike.

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The Spanish Slug

When I was 12 I read a book which involved an encounter with terrifying mutated slugs that fed on birds. So you can imagine my horror when 17 years later, I came across the Spanish slug, which is capable of terrorising bird nests. In our latest article of Norway’s invasive species, we look at what other forms of havoc this slug wreaks.

What are they?

Considered the most destructive pest slug in Europe, the Spanish slug, or Arion lusitanicus, or Arion vulgaris, or sometimes Geoff (there’s some controversy over the name, thanks to the fact that the Arion genus contains up to 50 species and they all look a lot like one another) is between 7-15cm long and can weigh up to 15 kilos if it’s sitting on a dog. They were originally thought to be from the Iberian peninsula, hence their name, but it appears that the slug doesn’t appear in Spain anywhere south of Catalonia, a controversy which recently ignited political unrest throughout the region. They are an incredibly slimy species, leaving trails wherever they go, however identification upon sight is made difficult by the fact that they can be a variety of colours, including yellowish, grey, reddish or brown, as can many of there aforementioned close relatives.

Arion-lusitanicus_Spanish-slug

When it comes to appearance, the Spanish slug is only as gross-looking as any other slug (Photo Credit: Wikipedia Commons)

How did they get here?

Geoff can now be found throughout the whole of Norway, with the exception of Troms and Finnmark. Soil and plants are the slugs food source and egg-laying sites, which means that potted plants have spread them throughout most of Europe. They don’t seem to discriminate between urban and natural habitats, which mean they can pop up pretty much anywhere. Those guys you seen covering the paths at twilight every day? Probably them.

What do they do?

They eat birds. Yeah I wasn’t joking about that. In a recent review of Geoff’s attack on birds, injuries of nestlings included “bleeding wounds, holes in the stomach with viscera exposed, vast skin lesions on wings, back, neck or head, partially eaten muscles or bills, even loss of eyes”.

But whilst horrifying, I should not pretend that this is one of the major threats the slugs pose. They are more likely to cause declines in native slug species before we see any impacts on bird populations. However they are a real threat to Norwegian crops. Like many successful invasive species, they will feed on a wide range of organisms, so while there has been no quantitative study on the economic impact of the slugs yet, there have been reported attacks on everything from potato fields to garden plants to sunflowers.

How do we stop them?

Prevention is almost impossible, as this would involve detailed inspection of all imported plants, which would potentially do little damage to a species which is already well established in Norway.

It is possible to reduce local populations by killing slugs. Decapitation or storage in the freezer are effective methods. Use of homemade explosives is considered excessive, and to be honest if that’s an option then you’re overqualified for pest removal. Elimination of eggs is also recommended, and slug fences (see here for an example) can help keep them out of garden patches. However the techniques are small-scale and labour intensive, and therefore not particularly helpful for the agriculture industry.

On a wider scale, some foreign parasites and beetle have been introduced as control measures, and slug pellets and other molluscides have been used in Europe. However the effectiveness is not proven yet, and some may have negative impacts on native species, and many molluscidal compounds are banned in Scandinavia.

For more information on the Spanish slug, we invite you to read the following studies

Invasive Alien Species Fact Sheet – Arion vulagris by the Online Database of the North European and Baltic Network on Invasive Alien Species

Arion slugs as nest predators of small passerine species – a review by Katarzyna Turzanska and Justyna Chachulska

The Greater Canada Goose

The Greater Canada Goose. Adorable when it's not chasing you down a street with blood in its eyes

The Greater Canada Goose. Adorable when it’s not chasing you down a street with blood in its eyes. (Image Credit: skeeze, CC0 Creative Commons)

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.

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