By the time David Lyall, lighthouse keeper, moved onto Stephens Island, a small species of wren was already having a tough time. The bird's last refuge was on Stephens Island. Less than two years after Lyall moved to the island, the bird went extinct; or rather, after Lyall and Tibbles moved to the island.
Extinct in a year
The year is 1894, and Lyall just started his new job as a lighthouse keeper off the coast of New Zealand, on Stephens Island. It's a lonely job being a lighthouse keeper, and you could hardly fault the man for bringing his cat along for the ride. This would prove to be disastrous for the wren, which now ironically carries Lyall's name.
Lyall's wren was distinctively flightless -- one of only four known songbirds that don't fly. All of these four species were inhabitants of islands, where they were safe from predators -- and all of them are now extinct... because they weren't really safe from predators.
Living Lyall's wrens were seen only twice. The lighthouse keeper described the 'rock wren', as he called it, as more fond of the night than the day, "running around the rocks like a mouse and so quick in its movements that he could not get near enough to hit it with a stick or stone". Lyall, to his credit, was involved in biological observations and communicated his observations to leading researchers of the time.
But Tibbles was less into biology, and more into hunting.
We don't know what Tibbles looked like, but we do know that when she came to the island, she was pregnant. She gave birth on the island, and at least some of her kittnes survived. Tibbles, as many cats do, brought "gifts" to its owner -- birds it had killed. As many a cat owner can attest, it's a nasty habit that hasn't changed much in recent years.
Often, Tibbles would bring the wrens it had killed. As the birds couldn't fly, they were easy prey. Lyall sent specimens to England for study, where Walter Buller, a bird expert, recognized it as a new species and reported it to the British Ornithologists' Union. But by the time that happened, the wrens were already doomed.
Around one year after he moved onto the island, Lyall writes to Butler: "…the cats have become wild and are making sad havoc among all the birds." A few weeks later, the Christchurch newspaper The Press writes a somber editorial:
"There is very good reason to believe that the bird is no longer to be found on the island, and, as it is not known to exist anywhere else, it has apparently become quite extinct. This is probably a record performance in the way of extermination."
It was indeed a very quick extermination of a species woefully unprepared for dealing with cats.
Over the following two years, several expeditions looking for specimens prove unsuccessful. Lyall is completely unable to find any more birds, and offers two specimens conserved in alcohol for the price of £50 apiece (over $5,000 in today's money) -- his yearly salary was £140 at the time.
Whether or not the birds went extinct exactly then or a few individuals lingered on for a bit longer is unclear, but they ultimately met extinction at the hands (or paws) of the newcomers.
The story of how a species was brought down by one cat spread far and wide, propagated especially by Walter Rothschild, a biologist who described the bird almost simultaneously to Butler. The two were fierce rivals.
But the account is likely not true, as New Zealand ornithologists found out. In a 2004 essay published by the Ornithological Society of New Zealand, two researchers pieced together the timeline of what happened on the island. It's likely that it wasn't Tibbles alone that sent the bird to extinction, but rather a population of cats -- either Tibbles' descendants or other cats escaped on the island.
In fact, the cats themselves suffered a grim fate, as the timeline shows:
- 1892: Work on building the lighthouse begins. Three lighthouse keepers and their families (17 people in total) were to move on the island. Construction worker F. W. Ingram makes the first observation of Lyall's wren, as he mentions "two kinds of wren" (the other one was probably the rifleman).
- 17–20 February: This is likely when cats were introduced to Stephens Island. At some point, a pregnant cat brought to the island escaped (probably Tibbles).
- June: Lyall reports that his cat is bringing wren carcasses. He sends the birds to England.
- April: Lyall writes to Buller: "…the cats have become wild and are making sad havoc among all the birds."
- November: no more wrens can be found on the island. Several subsequent expeditions are unsuccessful.
- 1897: The principal lighthouse keeper, Patrick Henaghan, requests shotguns and ammunition to destroy the "large number of cats running wild on the island."
- 1899: The new principal lighthouse keeper, Robert Cathcart, shoots over 100 feral cats since his arrival on 24 November 1898.
- 1905: Buller writes an article in which he quotes an anonymous source suggesting that lighthouse keepers stop bringing cats to islands: "And we certainly think that it would be as well if the Marine Department, in sending lighthouse keepers to isolated islands where interesting specimens of native birds are known or believed to exist, were to see that they are not allowed to take any cats with them, even if mouse-traps have to be furnished at the cost of the state."
- 1925: The last cats on the island were exterminated.
The cautionary tale is just as striking regardless of whether it was Tibbles alone or a group of cats that hunted the wren to extinction. Invasive species, even those who are cute and cuddly, can wreak havoc on native species.
The same problem, today
Whether she worked alone or not, Tibbles became an unwilling symbol of the damage cats can do -- domestic cats included.
A 2013 study estimated that domestic cats kill between 1.3 and 4 billion birds (in addition to up to 22.3 billion mammals) every year -- in the United States alone. This makes cats the most prolific killers in the animal kingdom by a mile. They are superpredators. In Australia, hunting by cats helped to drive at least 20 native mammals to extinction and continues to threaten at least 124 more.
While it may be possible that some of the birds killed by cats would be killed anyway, cats can put a lot of pressure on ecosystems, and many owners are not aware of this. The dangers are especially striking on an isolated island like Stephens Island and on a vulnerable bird like Lyall's wren -- but the damage is just as real in our cities and rural landscapes.
Predation by cats is a serious environmental problem, and it can't be solved without the help of cat owners. Unfortunately, surveys of cat owners find they often view the depredation of wildlife as "normal", and rarely feel an individual obligation to prevent it. Researchers are increasingly suggesting that owners should not let their cats roam outdoors, as this not only puts the cats themselves at risk (such as being run over by a car) but can also make the local environment safer. There are millions of Tibbles out there, and while we love them dearly, it's probably best for everyone if they spend more time inside and less time outside.