According to experts, legal changes are necessary to eliminate cat homelessness, limit their leaving homes and thus eliminate the pressure of this species on wildlife; the changes should include introducing the obligation to castrate cats, a ban on letting them out of the house without supervision and creating sanctuaries for cats living in the wild.

'The point is to take action in time, while ensuring the well-being of cats. This is our - human - responsibility. We should take these steps as soon as possible. Because we would not want to get as far as Australia or New Zealand, where the mass extermination of cats is currently taking place', says Michał Żmihorski. PhD, director of the Mammal Research Institute of the Polish Academy of Sciences. In Australia, the culling of cats began in 2015 because they threaten various wild species.

Żmihorski reminds that the research he conducted with his team (2019 'Global Ecology and Conservation') shows that every year in Poland, approximately 631 million mammals and almost 144 million birds fall prey to cats. Many of these animals are representatives of protected species.

That is why scientists and organizations involved in the protection of wildlife are expressing concern about the position of Małgorzata Tracz, an MP from the Green Party, who wrote on her Facebook profile at the beginning of February 2025 that 'free-roaming cats are not a problem'. This also sparked outrage among activists from foundations that help homeless cats. They emphasise that outdoor and free-roaming cats are at risk of premature death.

According to data cited in an interview with PAP by Katarzyna Udrycka from the 'Noga w Łapę' Foundation, in the USA, 1.5-3 billion birds fall prey to cats every year. 'This is twice as many as those that die as a result of collisions with glass. Predation is the first so-called direct cause of bird mortality. Polish and French studies show that cats mainly hunt mammals (primarily rodents, but also insectivorous shrews), but approx. 20 percent of cat prey are birds, followed by small reptiles and amphibians. However, these proportions may be different locally', the expert says. She adds that 144 million birds killed by cats every year in Poland is a huge number, considering that we have 100 million breeding pairs, which means that 200 million individuals start breeding.

Żmihorski estimates that such a large number of cat prey results primarily from the fact that, according to estimates, there are approx. 6 million cats. Foundations estimate that about 750 thousand of them are free-roaming. This data was also confirmed in the latest study 'The State of Pet Homelessness Project'.

The vast majority of cats living in houses are outdoor cats. In villages, it is rare for anyone not to allow a cat to go outside. Sometimes it is difficult to assess whether a cat that comes home once a week is a house cat or a stray cat', Żmihorski explains.

He adds that cats are also often poorly fed by their owners. 'We conducted interviews with farmers about what cats are given to eat. These are usually leftovers: bones, bread, even tea with milk', the scientist says. It is difficult for a cat to survive on such a diet, which is why it often has to hunt. 'Unfortunately, even a well-fed cat hunts, because that is its instinct. It is difficult to blame an animal for behaving in the way evolution has shaped it', the researcher explains.

In his opinion, the blame lies with cat owners who do not realize that their cats pose a serious threat to wildlife. 'Cats often kill animals and do not bring them back. They injure some animals, but these wounds also lead to death. This is the fraction of prey that escapes our estimates. Therefore, there may be even more victims', Żmihorski says.

He points out that cats in the environment can be a huge threat to rare, protected species, 'if there is a population of a rare species particularly vulnerable to cat predation in the area, such as hamsters or ground squirrels'. 'Cats can then cause catastrophic damage to nature', the expert assesses.

Interestingly, it seems that cats - contrary to popular belief - do not reduce the number of rats. 'In our studies, paradoxically, there were no rats among the animals that cats brought. Some argue that cats are necessary to control the population of these rodents. Meanwhile, there are studies showing that cats do not necessarily reduce the number of rats, but change their behaviour. Rats stop going out into open areas and become less visible to people, but their population size does not change', Żmihorski says. He adds that this was also confirmed by research conducted by his team in Wielkopolska.

Udrycka points out that according to the scientific definition, cat is considered an invasive species in the natural environment. 'Cat is on the list of alien and invasive species of the Institute of Nature Conservation of the Polish Academy of Sciences in Kraków', she says. Unfortunately, it is not on the list of invasive alien species posing a threat to the EU or on the list of invasive alien species posing a threat to Poland. This makes it difficult to take legal action that would help solve the problem of the pressure exerted by cats on wild species.

'Cat meets the definition of an invasive alien species because it did not evolve in Polish ecosystems, but was introduced to them. Since it did not evolve in a natural ecosystem, it has no natural enemies. Its presence causes damage to Polish fauna, which should be attributed to humans', Udrycka explains.

Żmihorski points out that cats also have the advantage of being supported by humans in the environment, for example, they are fed, so a periodic decrease in the availability of prey does not reduce the number of cats, as is the case with other predators.

Udrycka reminds that in its latest Summary Report from 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) at the UN lists invasive species as one of the five most important causes of global biodiversity loss. The International Union for Conservation of Nature (IUCN) has placed the cat on the list of invasive species because its presence in the natural environment has led to the extinction of various species of birds and mammals (birds: Guadalupe storm petrel, Lyall's wren; mammals: numbat, crescent nail-tail wallaby), mainly on islands. And it threatens others.

The expert reminds that according to estimates, wild species make up only 4 percent of the entire biomass of mammals on Earth. 'The rest are humans and breeding and companion species, including dogs and cats. The biomass of all cats living in homes and strays is almost twice as large as the biomass of African elephants and four times as large as the biomass of all elk in the world', the expert says.

Żmihorski points out that cats not only hunt and kill their prey, but also cause severe stress in them, which can weaken populations of wild animals, increasing their susceptibility to predator attacks. In addition, cats transmit diseases, interbreed with wildcats, which is why the population of these animals is endangered.

'The more research results and data we have, the more it is clear that the presence of cats in natural ecosystems is a serious threat to many species. I encounter cats in the Białowieża Forest; they are able to venture many kilometres from buildings. This problem requires wise actions, because we have only patches of wild nature left', the biologist emphasises.

In his opinion, decision-makers should understand that there are no free-roaming cats, just as there are no free-roaming dogs. 'These are homeless animals that should not be in natural ecosystems. We are responsible for limiting the free movement of both cats and dogs as much as possible', he says.

Experts emphasise that actions aimed at eliminating cat homelessness and banning them from leaving homes should also be implemented for the sake of the animals' well-being. 'We need to think together about solving this problem in a way that takes into account the protection of wildlife and the well-being of cats. If we pretend that the problem does not exist, we will lead to a situation where there will be more and more cats and then we will be forced to use radical solutions', Żmihorski concludes.

Joanna Morga (PAP)

PAP - Science in Poland

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