A local spotted this white cat at the fairy tern sanctuary.Courtesy of L. England

After the victims were found dead—“decapitated” and “breasts opened”—the residents of a beachside community in Mandurah, Australia, took matters into their own hands. Five locals, along with Claire Greenwell, a biologist at Murdoch University, arranged an overnight stakeout. Another neighbor lent them a mobile home, so they could take turns sleeping at the scene. The target of all this drama? A cat.

Specifically, a cat who had taken to killing in Mandurah’s bird sanctuary. Mandurah had recently fenced off nesting grounds to attract a vulnerable and cartoonishly adorable native seabird called the fairy tern. Fairy terns don’t usually nest near people, but to the city’s great pride and joy, they did start having chicks in Mandurah. It was a success story—until it wasn’t.

Over the course of a few weeks, the cat managed to almost singlehandedly drive off the entire nesting colony of 220 birds, according to a study from Greenwell and her colleagues in the journal Animals. The cat was directly or indirectly responsible for the death of six adults and 40 chicks. Once it became clear the sanctuary was no longer safe, the entire colony abandoned the site. The nesting sanctuary was ultimately a failure.

A fairy tern feeding a chick (Claire Greenwell)

The first sign of something amiss came on the night of November 18, 2018, when residents heard a commotion among the fairy terns. A white cat was chased out of the sanctuary. In the days and weeks after, Greenwell started finding dead birds—or really, parts of dead birds. Other birds went missing. The death of an eight-day-old chick, the first to hatch in the entire nesting colony, hit Greenwell particularly hard. “Every single day, I watched that chick grow,” she says. “The parents were looking for it. They wouldn’t leave the nest, because they were waiting for the chick to come back.”

Meanwhile, residents saw a cat prowling in the area again. It was white. Over the next few days, as birds kept dying or disappearing, wildlife cameras confirmed the presence of the white cat. A resident even snapped a photo from an apartment balcony, in which the cat appeared to be in the sanctuary eating something.

That’s when they decided on the stakeout. On the night of December 1, Greenwell and the five residents took shifts. The white cat came at 7 p.m.; they shooed it away. The cat returned at midnight; they shooed it away again. The cat came back a third time that night, and Greenwall saw it slinking toward the birds. They chased the cat for half a mile before it disappeared in the coastal scrub. The group returned to stake out the area the next night, and then the City of Mandurah hired an overnight security guard for a few days. When the cat was not seen again, they thought the danger had passed.

But it had not. The cat returned, and more dead birds turned up. What’s more, Greenwell observed, the adults stopped spending time on the ground caring for the chicks. They also stopped working together to drive off raptors hunting for chicks, which adult fairy terns normally do by flying around and above the nests in a big group. The birds seemed to have given up on protecting their chicks. “The colony basically just fell apart,” she says. By mid-December, the colony had left, and all the chicks were dead.

(During this period, two other cats, both identified as pets, were also trapped at or near the site, though there’s no evidence either hunted birds. The fairy tern deaths continued after these cats were removed, too. No other cats were caught on camera or seen by residents at the time.)

“There was absolute outrage in the community,” Greenwell says. The residents had become so invested in the fairy terns that one of them was waking up in the middle of the night to check on the birds. In July, the city council moved forward on a law cracking down on cat ownership. The law would require a permit for more than two cats, prohibit cats from certain nature reserves, and fine owners $200 not following permit rules or for letting their cats cause a nuisance.

All of this comes at a time when the Australian government is attempting to cull 2 million feral cats—through trapping, shooting, and even dropping poisoned sausages. In Australia, these measures are meant to help save native species. The continent’s birds, mammals, and reptiles evolved over millions of years without cats, leaving them especially vulnerable to feline predation. “Cats have been a driving factor in the extinction of most of the 34 mammals that have gone extinct in Australia,” says John Woinarski, a conservation biologist with the Threatened Species Recovery Hub.

In Mandurah, the white, male cat was finally captured on December 12 and, according to local news reports, euthanized by the City. The cat was not microchipped or collared, but it had been neutered.

In the U.S., where pro-cat groups have gained more purchase than in Australia, cat advocates promote an intensely controversial policy of trap-neuter-return (TNR), in which neutered cats are released back outdoors. Cat advocates tout trap-neuter-release as the humane way to reduce feral and stray feline populations over time. Bird advocates say the policy doesn’t work, because TNR programs often aren’t able to spay or neuter enough of the cats. In any case, neutered cats, once returned, are killing wildlife, Greenwell says. In Australia, the country has decided its native wildlife is more important.

Of course, not every single cat is as destructive as the white cat in Mandurah. “Cats can be quite idiosyncratic,” Woinarski says. Some are excellent hunters. Others not so much. Elsewhere in the world, people have also reported a single cat having a huge and disproportionate impact on a group of birds. And cats certainly do sometimes kill more prey than they eat. A study of stray cats on Jekyll Island, off the coast of Georgia, found that they ate just 83 percent of what they killed.

A cat with a woodrat in its mouth in the Florida Keys (Michael Cove)

The abandonment of the fairy tern nesting site also demonstrates how the impact of cats ripples far beyond the birds that they directly kill. “Whether they’re actually killing or not, they can incite fear in these small prey populations,” says Michael Cove, a biologist with North Carolina State University. Scientists call this the “landscape of fear.” In the Florida Keys, for example, where Cove has studied free-ranging cats, he thinks endangered Key Largo woodrats have been building fewer of their characteristic nests out of large sticks. “If you’re a small rodent carrying this big, cumbersome stick,” Cove says, “that makes it pretty obvious, almost advertising yourself in the world. You can imagine that you become easy prey.”

The very presence of cats—or perhaps even a single cat—is enough to change an ecosystem.

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