The Kerguelen Islands lie deep in the southern Indian Ocean about halfway between Madagascar and Antarctica. The average annual temperature is 4.5 ̊C, wind speeds reach up to 150kph and it rains or snows for 285 days a year. Like South Georgia or the Falklands, which are on a similar latitude, the archipelago is ideal for albatrosses, petrels and other seabirds to raise their chicks in the absence of ground predators. Or it used to be.
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Incredibly, despite the harsh climate that is about as far removed from their Middle Eastern origins as can be imagined, domestic cats survive on Grand Terre (the main island) on a diet of non-native rabbits and mice, and burrowing petrels. Recently, some cats have started to hunt wandering albatross chicks.
The cats have been here since at least 1876, and in the late 1990s the population was estimated at about 7,000 individuals. A study published in Ecosphere in 2024 found that 25 per cent of albatross chick mortality was a result of cat predation. “Without cat control, some albatross populations would markedly decline,” the scientists reported.
Chris Lepczyk, an ecologist at Auburn University in Alabama, has spent more than 20 years studying the impacts of domestic cats on wildlife, and says those in Kerguelen offer a great example of just what impressive predators they are.
“They have the ability to live in extreme environments, they don’t even need sources of fresh water,” he says. “You can have albatross nests – and you can see this in Hawaii, too – and one cat can go in and destroy a whole colony.”
Do cats kill wild animals?
Cats have a hugely negative impact on wildlife on islands, particularly where that wildlife has not evolved to cope with mammalian predators. For example, feral cats were responsible for the extinction of the Stephens Island wren in New Zealand and have been linked to the severe decline or extinction of 30 species of forest birds in Hawaii.
On continental Australia – which has a unique population of largely marsupial mammals – their effect is almost equally catastrophic. Two-thirds of total mortality of brush-tailed bettongs, or woylies, is down to introduced cats, while another study found that native long-haired rats (a rare Australian placental mammal) went extinct in enclosures where cats were also present.
One 2013 study in the USA found that free-ranging cats killed an almost incomprehensible number of animals every year – 1.3-4 billion birds, 6.3-22.3 billion mammals, 258-822 million reptiles and 95-299 million amphibians. In the UK, an oft-cited piece of research from 2003 reports that Britain’s nine million cats brought home 57 million mammals and 27 million birds in just five months – and therefore actually killed even more than that.
How can I stop my cat from killing wildlife?
Lepczyk believes it’s time that cat-owners started to accept the necessity of putting constraints on their pets’ freedom, even curtailing their right to roam outdoors. “Cats need to be indoors,” he says. “You can have ‘catios’ if they need to be outdoors or you can have them on a leash, like a dog. They need to be sterilised, and I would also argue for [mandatory] licensing and microchipping.” The UK introduced compulsory microchipping in June 2024.
Lepczyk argues that cats would live healthier, longer lives if they were prevented from going outdoors, and it would also have benefits for humans. They would be unable to pick up diseases such as toxoplasmosis, which they pass onto us and which has been linked to higher rates of divorce and car accidents (through ensuing changes in personality traits and behaviour). It may lead to partial blindness and even miscarriages, he suggests.
In the UK, conservation scientists are also trying to address the issue. But instead of concentrating on the impact cats have on wildlife, a research programme at the University of Exeter that ran for three years focused instead on the attitudes of cat owners and what changes they could make to how they care for their pets that would make a difference to predation rates.
As environmental social scientist Sarah Crowley, who led the project, explains, one of the biggest takeaways is that what motivates cat owners is not concerns about wildlife. “From our experience, most people’s primary concern and key responsibility is for their cat,” she says.
That’s not to say people don’t care if cats hunt and kill wild animals – but it might be because they don’t like the idea of suffering (as distinct from the conservation impact) or, indeed, for more selfish reasons. “It might be because they don’t like stepping on dead things in the middle of the night,” Crowley points out. “I have stood in mouse entrails in my bedroom, and it’s not funny.”
Two key pieces of research carried out by Crowley and her colleagues involved diet and play. They found that switching cats to a high-protein diet consisting mainly of fresh meat reduced the quantity of prey they brought home by about a third. Playing with cats for 5-10 minutes a day also reduced kill rates. And, crucially, these can be ‘sold’ to cat owners as desirable because they improve the quality of their pets’ lives, not because they benefit mice and robins.
Other innovations have had mixed success. Bells, for example, work with some cats but not others. Brightly coloured ‘Birdsbesafe’ collars (which look like garish ruffs) were found to be effective in reducing predation of birds, but some cat owners expressed concerns about their pets’ welfare, and there was also an element of people thinking cats looked silly in them.
Crowley is now working with wildlife conservation organisations, cat welfare groups and others to produce a set of guidelines based on the current evidence on what pet owners can do to reduce hunting behaviour. She believes this will have real outreach because it is endorsed by such a wide range of stakeholders that do not normally share common ground.
What about feral cats?
In Australia and New Zealand, there is a much more robust attitude towards dealing with cats through culling programmes, though it’s also the case they have a bigger conservation impact because of the endemic wildlife that has evolved without any ground predator equivalent to a cat.
But it’s also true, as Crowley points out, that attitudes to pets have shifted here in Britain. “We have legislated for cats to be microchipped, and neutering rates in the UK are very high,” she says.
Lepcyzk believes that people in the USA are also starting to change. “We’ve done social science that suggests the number of people who want cats to stay the way they are and not be managed is quite a low percentage of the population,” he says. “A lot of people don’t like seeing cats outdoors, they don’t like [feral] cat colonies, they don’t like seeing mortality events.”
But he laments that despite this, there hasn’t been a sufficient push within society to make any practical difference. The question now is whether Crowley’s research can demonstrate that a more nudge-based approach can deliver results.
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