Cats and dogs – the most destructive invasive species of all?

Cats and dogs are the most popular pets around the world. Several hundred million individuals of each species live in households worldwide. In the EU alone, there are 85 million pet dogs and around 75 million pet cats. But these numbers actually still represent the smaller part of dogs and cats alive. Around twice as many individuals live feral as stray animals without an owner. While owners love their pet dogs and cats, these animals pose a risk to wildlife, livestock and even humans.

Dogs are more dangerous than wild carnivores

Actually, dogs are by far the most dangerous animals when you go by the number of attacks. In the United Kingdom alone, dogs attacked over 5 000 people within one year. Many call for large predators like the wolf to be killed, because they fear for the safety of their children. At the same time hundreds of millions people around the globe live with predators in their own homes. Compared to 5 000 dog attacks there are almost no confirmed attacks on humans by wolves in Europe.

Dogs are also responsible for a large part of livestock kills. Dogs killed 15 000 sheep in the UK alone in 2016 compared to 21 000 sheep killed by wild large carnivores in the whole EU. For stray dogs, livestock is often the easiest prey and other than wild carnivores, they do not avoid settlements. In Germany, 60 000 stray dogs get killed every year to control the damage they cause. And the numbers of attacks on humans and livestock are still rising with an increasing number of dogs in many countries.

Cats are dangerous predators for wildlife

While cats normally do not pose a threat to humans or livestock, they are the most destructive invasive predator in the world. They are at least partly responsible for the extinction of at least 63 wildlife species. While most pet dogs are supervised, when they are outside, cats often roam free. This allows them to freely follow their hunting instinct, killing birds, small mammals, reptiles and amphibians.

cats-and-dogs.jpg - European Wilderness Society - CC NonCommercial-NoDerivates 4.0 International
Cute for sure, but also a serious threat to human and animal lives

What are the legal consequences?

Cats and dogs do not only impact wildlife through direct predation, but also through disturbance, prey competition, spread of disease and hybridisation. Two legal experts at Tilburg University in the Netherlands did a study what this impact means in respect to the Habitats and Birds Directives, the main species protection legislation of the EU. They found that cats kill around 140 million animals per year in the Netherlands and pose a threat to 370 species.

The two directives oblige member states to protect all bird species, all endangered species and Natura 2000 sites. House cats are a species from Africa that was brougth to all parts of the world by humans. They pose a threat to many endemic birds and other endangered species and by scientific standards we must consider them an invasive species. Hence, the experts conclude that stray and feral cats must be controlled and removed, if necessary. They even go one step further and say that pet cats cannot roam freely.

“This conclusion may come across as extraordinary, but it really is the outcome of a standard interpretive analysis of legal requirements that have been around for decades, in light of current knowledge on cats’ biodiversity impacts.”

Arie Trouwborst
Tilburg University

The European commission was quick to deny any plans to force cat owners to keep their animals inside or put them on a leash. However, this study shows that we apply a double standard to our pets. On one hand, we put great effort into species conservation and often blow wildlife attacks out of proportion. On the other hand, we ignore the damage cats and dogs cause to wildlife and the danger especially dogs pose not only to wildlife, but also to livestock and humans.

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