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Free-ranging cats are one of the most problematic invasive species

A recent study from Auburn University has brought to light a concerning environmental issue: the impact of free-ranging pet cats. 

The extensive research provides a detailed analysis of how domestic cats are causing significant ecological damage.

Ecological disruption

The study categorizes free-ranging cats as one of the most invasive species in the world, contributing to widespread ecological disruption. 

The experts found that free-ranging cats have consumed over 2,000 species, 347 of which are listed as threatened or of higher concern on the International Union for Conservation of Nature (IUCN) Red List. This alarming fact highlights the predatory impact of cats on biodiversity.

“Since house cats (Felis catus) were domesticated over 9,000 years ago, humans have introduced them across much of the world,” wrote the researchers.

“Today, cats inhabit all continents, except Antarctica, and have been introduced to hundreds of islands, making them amongst the most widely distributed species on the planet. Because of this cosmopolitan distribution, cats have disrupted many ecosystems to which they have been introduced.”

Problematic invasive species 

Beyond their predatory habits, free-ranging cats pose another threat by spreading diseases that affect both wildlife and human health. These include parasites that weaken immune systems and more severe diseases like plague and rabies. 

“Specifically, cats spread novel diseases to a range of species including humans, out-compete native felids and other mesopredators, threaten the genetic integrity of wild felids, prey on native fauna, and have driven many species to extinction,” wrote the study authors. 

“As a result, free-ranging cats (i.e., owned or unowned cats with access to the outdoor environment) are amongst the most problematic invasive species in the world.”

Focus of the study

The researchers set out to assess the species consumed by cats on a global scale. They analyzed video footage, as well as data from 533 relevant studies published through May 2021.

In particular, the team wanted to determine the degree to which cats consume different animal species, whether there are any species that cats avoid consuming, and if cats have dietary preferences based on prey size.

Alarming results

The findings were startling: approximately 47% of the diet of free-ranging cats consisted of birds, 22% reptiles, and 20% mammals, along with insects, amphibians, and other prey.

“Of 544 studies, 533 met our criteria for species-level data and included 2,084 species eaten by cats. Notably, these 2,084 species provide a conservative estimate of cat diet based on species accumulation curves, indicating that as more studies are conducted, we will discover many more prey species,” said the researchers.

Broader impacts

The experts noted that while the focus of their research was on cat diet, it builds upon over 150 years of literature documenting the negative impacts that free-ranging cats pose to the environment. 

“Aside from predation, these impacts include numerous cat-borne diseases that impact wildlife and human health and well-being, including toxoplasmosis, plague, and rabies, and in some regions (such as Australia), some of these diseases would not occur without cats.”

“Furthermore, free-ranging cats living in clowders (aka colonies) can exacerbate these problems as well as present additional problems including excess nutrient loading, sanitation, and wildlife conflicts.” 

Indiscriminate predators 

The experts explained that the mere presence of cats outdoors creates a “landscape of fear” that can affect the foraging decisions and reproductive success of other animals.

“Collectively, our findings demonstrate that cats are indiscriminate predators and eat essentially any type of animal that they can capture at some life stage or can scavenge. This dietary breadth lends further evidence to the myriad ways that cats can (or may) interact with native species and disrupt ecosystems because they are not dependent on any one trophic level or taxonomic group,” wrote the researchers.

“As a result, cats are influencing a broader set of species interactions than previously understood. Ultimately, while our results are conservative, they highlight the degree to which a widely distributed invasive species is interacting with species around the world, which is critical information for furthering conservation, management, and policy work.”

The study is published in the journal Nature Communications.


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