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A wet, rugged landscape of soaring mountain peaks, vertical cliff faces and green valleys, Kauai’s uninhabited northwest corridor is home to hundreds of varieties of threatened and endangered plants and animals — some of which survive nowhere else on earth.
Once found in abundance throughout the Hawaiian islands, the critically endangered Newell’s shearwater and Hawaiian petrel populations now exist almost exclusively in the mountains of Kauai, where predator cats, along with rats and barn owls, prowl freely. The birds, which are nocturnal and nest in underground burrows, have no defenses for these invasive assassins.
Due to these invasive enemies, and threats like light pollution, the population of both seabird species in recent decades has plummeted perilously near to extinction.
Barn owls are capable of swooping down and stealing an adult seabird, while rats, which have a steady presence in seabird nesting habitat, team up to feed on helpless chicks and eggs — a staggering blow for species that lay and incubate a single egg per year.
Even with predator control, a feral cat has the capacity to decimate large sections of a breeding colony, arriving suddenly and, in a single event, wiping out multiple adult birds, as well as chicks and eggs, before fleeing the scene without a trace.
Without predator control, a cat could take out the whole colony.
Employing satellites and science that allows researchers to reconstruct the diets of deceased animals, a pair of predator control specialists who work to protect imperiled native animal species on Kauai are becoming increasingly effective at targeting feral cats in the open jungle.
Captured by game cameras, images of feral cats raiding burrows with mouths full of feathers have been shared widely by Hawaii environmental regulators and conservationists on social media. The images help dispel the perception of free-roaming cats as cute and innocent creatures, promoting instead the idea that invasive felines in the wild could mean a death sentence for vulnerable wildlife.
“Cats are the big flashy target predator that everyone is really passionate about,” said biologist Alex Dutcher. “It’s an endless game of cat and mouse, for lack of a better expression, trying to predict their movements, lure them into our traps and trying to prevent these dramatic and potentially devastating events.”
Adult birds gobbled by predators are especially difficult to replace. When a chick hatches, it fledges and soars out to sea, returning to the breeding colony after five or six years on the wing. Only then does the bird dig a burrow and lay its first egg.
“For it to come back here and start a burrow and get hit by a cat — that’s a huge loss,” said Kyle Pias, a biologist who has been working to control seabird predators on Kauai since 2015.
In recent years, new cat tracking and trapping techniques have yielded promising signs that fewer seabirds are succumbing to the teeth of feral cats.
In one prime nesting area for endangered Kauai seabirds, the number of seabirds killed by cats and observed by researchers has dropped from 31 birds in 2016 to 11 birds in 2017, according to data cited in a press release by the state Department of Land and Natural Resources. Last year there were five recorded deaths in the same region.
“People say, ‘So what? Thirty-one doesn’t sound like a whole lot of birds,'” said Pias, who led the research team. “But those are just the ones we found in a small area along the trails we can access. So there are likely many more. That number is a proxy for how often predation is occurring in the colony itself, which is a vastly larger area.”
There are other threats. When Newell’s chicks emerge from their burrows and make their first nocturnal flight, they navigate to sea by relying on moonlight. Artificial light can confuse the birds, causing them to collide with utility poles or buildings and fall from the sky.
Both species are prone to injurious, sometimes deadly, collisions with power lines.
Neither of these risks exist in the birds’ hard-to-access breeding colonies on the slopes of Kauai’s little-traversed mountains. Here in the breeding colonies, feral cats are considered the biggest killers of seabirds.
Dutcher and Pias have been trapping cats and other seabird predators on Kauai for years, most recently as co-owners of Hallux Ecosystem Restoration, a new private company they launched in May.
Focusing their efforts on removing feral cats from the wilderness landscape, the scientists take a varied, adaptive approach, luring cats into cage traps with the aid of pungent sardines, flashy aluminum, pheromones and camouflage.
“Every cat is different,” Pias said. “If you only have one type of trap out, you’re not going to catch every cat.”
Rather than catch every cat in the wild, Pias said he and his team instead try to ascertain which cats are most likely to hunt seabirds and then target those cats specifically.
The science of figuring out which cats are most inclined to prey on seabirds is still evolving.
Not all cats target seabirds for a good meal. But every cat in the wild has the potential to become a seabird hunter.
Some cats — those that have acquired and demonstrated the skill to stalk the birds as prey — have earned themselves inclusion on Pias and Dutchers’ list of highest value targets. But since the going theory is that seabird hunting is a learned behavior that cats acquire over time, the scientists also seek to remove non-seabird eaters from breeding areas.
The simplest way to track a seabird-hunting cat is to take note of its markings when a game camera catches it roaming in a seabird ground-nesting zone. Scientists then attempt to match those markings to the coats of cats caught in their traps.
To determine whether that particular cat had been a hunter of seabirds, Pias and Dutcher examine the cat’s stomach contents. But if a cat hasn’t eaten a seabird during the 48 hours before it was trapped and killed, all signs of a seabird meal will be gone.
To that end, Pias and Dutcher have begun to airmail feral cat tissue samples to a doctoral student at the University of Akron in Ohio. In a research lab, the doctoral student is conducting isotope analysis of the tissue samples to try to discern whether the cat had consumed seabirds at any time over the course of its dietary history.
This is the same science used by the U.S. Department of Defense to identify the bone fragments of soldiers killed overseas. It’s also used by food regulators to spot imitation Kobe beef.
For Pias and Dutcher, isotope analysis allows them to peek beyond a feral cat’s 48-hour digestive window to see whether it ate seabirds at any point in its life. The results could eventually yield clues about how cats learn to hunt seabirds.
Furthering the duo’s efforts to effectively target seabird-killing cats, Dutcher has started using satellite collars to track the movement of cats in the wild. Her research is helping scientists decide where to set their traps, and it marks the first time satellite collars have been used on cats on Kauai.
By studying the precise GPS locations of feral cats moving around the jungle, Dutcher is starting to chart paths of least resistance — trails that are markedly easier for cats to traverse amid the challenging terrain of cliffs and plunging ridgelines. Dutcher and Pias have already relocated some of their traps onto those passageways, making their efforts more effective.
The data is also revealing how far and wide feral cats roam in the jungle. Dutcher said cats tracked by satellite are covering a surprisingly vast amount of acreage.
With the help of all these techniques and more, Pias said more cats are being removed from the Kauai jungle, giving seabirds a better chance at survival.
“I think it’s just persistence and a willingness to adapt and try new things,” Pias said.
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