Cats are not picky. As beloved companions of humans, cats still pose a real threat to wildlife, according to the results of a study aimed at quantifying our cats' diets on a global scale. These natural hunters eat more than 2,000 species around the world, hundreds of which are already endangered or threatened with extinction. Their pretty, harmless-looking faces contribute to the decline in biodiversity. The researchers behind the paper, published Tuesday, December 12 in Nature Communication, even describe cats as “one of the most problematic invasive species in the world.”
“Our study sheds light on the predatory habits of one of the world’s most successful and widespread invasive predators,” write the American authors from Auburn University of Forestry, Wildlife and Environment in the US. Since their domestication 9,000 years ago, cats have spread to every continent except Antarctica. A spread that impacts the natural food chain: birds, mammals, insects and reptiles are on the menu. “Cats eat everything that is in their environment,” the researchers note. “If a species is missing from the analysis of its diet, it is likely that that prey is simply missing or rare” in its habitat.
In total, free-roaming domestic cats eat 981 species of birds, 463 reptiles, 431 mammals, but also 119 species of insects and 57 species of amphibians. That means around 9% of known bird species, 6% of known mammal species and 4% of known reptile species – and 17% of all of these species are the subject of conservation measures, the study says. Scientists achieved such results by compiling more than 500 existing studies that included a list of species consumed by cats in a given area. The researchers then checked whether the prey was on the International Union for Conservation of Nature's Red List of Threatened Species.
“Simple measures” and “harmless” aids
Cats are particularly dangerous on islands, where the risk of extinction is greater than on continents. This is the case in New Zealand, where cats have eaten birds that are now extinct in the wild, such as the Stephen's xenic or the New Zealand quail. Their impact on wildlife has also sparked lively debate in the country. Authorities are finding it difficult to respond to the problem of these free-roaming cats, and even organized a hunting competition for children last spring to kill stray cats – which was narrowly canceled.
According to a study by the Australian NGO Invasive Species Council, which advocates for the introduction of cat curfews, cats kill more than 300 million animals every year in Australia alone. This solution has even been considered in a German town, Walldorf, where residents were ordered to confine their cats for three months in the spring to protect the reproduction of crested coches, a bird similar to the lark.
“Adding bells to collars and keeping cats indoors at night are simple measures” to mitigate their impact on wildlife, a spokesman for the Royal Society for the Protection of Birds, the largest animal protection organization in Europe, responded, quoted by the Guardian. He also praises the effectiveness of “ultrasonic devices,” a “harmless but effective way to reduce the time cats spend in gardens,” as cats pose a terrible threat to ground-nesting birds. These organization-approved devices emit ultrasound when they detect a cat's movement and body heat, deterring them from entering the yard. They should have no impact on people or the environment. Soft solutions that make it possible to better regulate the environmental impact of those who are often considered a full member of the family.