Biologist Liana Zanette was first drawn to Rithet’s Bog just north of Victoria, because she wanted to study what happened when sparrows get scared.

She set up 24-hour infrared cameras at song sparrow nests to record when they were devoured by suburban predators. Then, by comparing the Rithet’s Bog sparrows to those on the predator-free Gulf Islands, she could figure out how well sparrows could raise their children when under the constant threat of becoming dinner.

But starting in 2010, the Rithet’s Bog sparrows began to disappear — fast. By 2011, Zanette had been forced to stop her study.  “There were hardly any birds left … from my point of view, there was no point continuing a study without any song sparrows to work on,” she said.

The reason? Cats. “The number of cats that we saw out there was just off the scale. The numbers were astronomical,” said Zanette. They had been brought there by well-intentioned neighbours who had taken to trapping feral cats, neutering them, and then releasing them back into the wild.

Video captured by Liana Zanette showing song sparrow nestlings at Rithet’s Bog being eaten by a suspected feral cat. More videos at this link.

The neighbours were following a protocol widely accepted as the most humane way to deal with feral cats. Known as TNR (trap, neuter, return), it’s endorsed by the BC SPCA and the Canadian Veterinary Medical Association. But the effect on the Rithet’s Bog sparrows was devastating; as Zanette’s video cameras captured, they were eating baby sparrows like popcorn.

North America is in the midst of a disastrous plunge in bird populations. According to a recent study in Science, the continent has lost three billion birds since 1970; a population decline of nearly one third. Amid this, the biggest single cause of bird death  — bigger than hunting, window strikes or even wind turbines — is the housecat. Every year in Canada, cats kill between 100 and 350 million birds. Every bird in southern Canada has a roughly one in 14 chance of meeting its end in the paws of a cat. As Victoria’s experience shows, if we want to save the birds we might have to start thinking hard about locking up our cats.  

Victoria in particular stands as one of the deadliest places for songbirds in the entire country. According to a 2013 Environment Canada study, the rate of cat-caused bird deaths in southwestern B.C. was rivalled only by the much larger cities of Toronto, Montreal, and the Lower Mainland.

In some cases, house cats have singularly contributed to the virtual disappearance of Vancouver Island bird species. The streaked horned lark, once a resident of southern Vancouver Island, is now likely locally extinct in Canada, and cats were cited as one of the main causes of nest failure. The last streaked horn lark able to breed was recorded in 2002.

The coastal vesper sparrow has seen its population drop by 85 per cent over the past decade, and a federal government analysis cited a “high concentration of domestic and feral cats” as factors in their decline. The last known breeding pair in Canada was observed in 2014 near the Nanaimo Airport, right within a known hunting ground for nearby feral cats.

Victoria maintains a dense network of known feral cat colonies that are the product of “trap, neuter, return.” Instead of having feral cats euthanized, volunteers trap and neuter cats in feral colonies, and release them back into the environment where they are fed and monitored. The goal is for the colony to disappear over time as the cats find homes or die out. Ever since 2010, this policy has been explicitly backed by the BC SPCA, which “supports the concept of well managed colonies where the principle (sic) goal is ending homeless and feral cat populations.”

In and around Victoria, there are nearly 30 cat colonies mapped out by Dee’s Orphan Kitten Fund, a group that runs trap-neuter-return programs in the region. In 2012, that same group estimated that a colony of 40 to 50 cats lived near Rithet’s Bog, the Saanich municipal park where Liana Zanette was forced to halt her song sparrow study.

Feral cats are particularly deadly around Victoria because the area’s mild winters make it a desirable stopover for songbirds. Those same mild winters also mean that Victoria cats can hunt year-round. And without having to worry about their own predators, such as coyotes, the Victoria feral cat can be assured a much longer life — which it will largely fill with more hunting.

“These birds are flying thousands of kilometers; it’s already really tough,” said Tanya Luszcz, a biologist and program manager with Partners in Flight B.C. of the Canadian Wildlife Service at Environment and Climate Change Canada. “They have to find food … they have to defend their habitat. It just feels really unfair that a cat is potentially taking that bird out of the population when we already have other threats.”

Around the world, cats have been singularly blamed for the extinction of more than 60 species, according to a 2016 study in the Proceedings of the National Academy of Sciences. A flightless wren on an island off New Zealand went extinct in 1895, less than a year after the arrival of a lightkeeper’s cat named Tibbles. In Hawaii, cats — including those from “managed” colonies — are known to attack the nests of endangered nēnē geese. Last year in Australia, a single neutered cat wiped out an entire colony of threatened fairy terns; it decapitated adults, ate chicks, and destroyed 111 nests.

A National Geographic video about the University of Georgia Kitty Cams project, which used cameras to track the hunting habits of feral cats.

Some surveys put a single cat’s body count at 20 to 50 birds and 160 to 350 mammals per year, though these numbers are thought to be low estimates because of the difficulty in tracking each kill. Even when cats aren’t successful in the hunt, their presence alone can cut birds’ reproductive capacity nearly in half.

Out of instinct, most cats will hunt and kill even when they’re not hungry and have no biological need, said Ann Nightingale, a coordinator and former president of the Victoria Natural History Society. “It is in their nature,” she said. “Cats are just one more way, in my opinion, that we have invented to kill birds — one of the few that we actually have control over.” Earlier this year, the society urged municipalities around Victoria to adopt licensing laws to protect birds from roaming cats and protect cats from disease and human activity.

In Victoria, bylaws prohibit owners from letting their cats roam free and offenders face a $150 fine. After a four-hour debate on Sept. 30, Saanich’s council unanimously voted down a motion to bring in similar controls for housecats. Meanwhile, neither municipality has a policy when it comes to feral cats.

The Canadian Veterinary Medical Association supports the use of “well-managed (trap-neuter-return) programs as an important strategy in the management” of feral cats, with the condition that colonies should not be located near ecologically sensitive areas. The BC SPCA also acknowledges that cat colonies can negatively affect nearly wildlife, which is why they urge cat colony volunteers to draw up wildlife mitigation strategies. “It’s a tough situation,” said Dr. Sarah Armstrong, a veterinarian and board member of the BC SPCA. “Trap-neuter-return is just the best halfway point.”

That’s particularly true when the alternative is a cull. In feral-cat-plagued Australia, for instance, officials recently set a target of killing two million cats by 2020. But in Victoria, given the public recent outcry at attempted culls of Oak Bay deer or UVic’s feral rabbits, it’s clear that any talk of feral cat euthanization could spark overwhelming pushback.

“In response to why we don’t euthanize all free-roaming cats to protect birds: It is not publicly considered acceptable by the majority of the population to euthanize cats and science demonstrates that (trap-neuter-return) is effective, so we follow that scientifically proven method,” wrote Marieke van der Velden, the BC SPCA outreach specialist in a statement.

As for the science behind colonies, the nonprofit cites a number of sources on its website. One is a 2003 case study of a trap-neuter-return program that successfully eliminated a feral cat problem on an American university campus. Another was a 1999 study showing the much lower stress levels on cats with room to roam. The organization also cites several public opinion surveys, including one by the U.S. advocacy group Alley Cat Allies, which concluded that euthanizing feral cats is “at odds with the humane values of most Americans” However, none of the BC SPCA’s cited studies directly investigate the effects of feral cat colonies on local wildlife.

Arguments in favour of cat colonies have often come under fierce condemnation from biologists, many of whom, like Liana Zanette, are seeing the direct consequences of free-roaming cats. A 2009 paper in Conservation Biology noted that in the rare case that trap-neuter-return programs reduce the number of feral cats, they come from sustained efforts by scientific researchers — not neighborhood volunteer groups.

A particularly scathing 2018 article, also in Conservation Biology, accused  accused pro-TNR activists of pushing “misinformation strategies” that were anti-science and threatening biodiversity around the world. “The end game for these merchants of doubt is protected status and a continued free‐ranging existence for this globally harmful invasive species,” it wrote.

There is a positive side to cats being the number one killer of birds in Canada: It’s actually a relatively easy problem to address.“Cats should be low-hanging fruit,” said the Canadian Wildlife Service’s Tanya Luszcz. “It’s something that we can do something about.”

Owners can keep cats inside, or construct “catios” to allow safe outings in the outdoors. Widespread spaying and neutering can prevent more unwanted cats being released into the landscape to hunt birds. Municipalities can enact licensing systems and bylaws that restrict cats from roaming.

And despite their disagreements over feral cats, conservation advocates and cat enthusiasts do have some common ground. A 2013 study concluded that both groups generally agree on the need for mandatory licensing and neutering, as well as non-lethal population control.

Meanwhile, at Rithet’s Bog, cats are still calling the shots. Russ Pym, president of the Rithet’s Bog Conservation Society, says that in addition to disappearing song sparrows, he’s seen a  general decline in voles and songbirds, among others.

If dogs were the ones wreaking havoc in Rithet’s Bog, conservationists could at least call animal control. But as laws stand in Greater Victoria, there is nothing to stop a colony of feral cats, even one that has taken refuge within a nature reserve.

Said Pym, “A nature sanctuary is supposed to be protecting our native species. A cat is a non-native species; it doesn’t belong.”