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Guam's slithery problem

Volunteers battle brown tree snakes on Cocos Island

By Dana Williams

We stepped onto the pier at Cocos Island armed with extension poles, powerful flashlights and airsoft rifles.

There was less than an hour of daylight left. Then the snakes would come out, slithering high above our heads.

Whether we would find them would be another matter entirely.

For the last two years, Friends of Islan Dano, the CHamoru name for Cocos Island, have been faithfully organizing Saturday night trips to hunt the brown tree snake. While the snake has devastated Guam’s bird population, the strip of land about a mile south of Malesso’ has provided a sliver of hope that birds and other species could be saved.

If the volunteers in this community posse succeed in their quest to retake the island, they will make history.

No invasive snake species, once established on an island, has ever been eradicated.

Writer Dana Williams displays the snake she spotted while accompanying Friends of Islan Dano on a July 22 trip to Cocos Island. Contributed photo

'It could happen on Cocos.

For more than 70 years, Guam has been plagued by the ecological consequences of the brown tree snake. From wiping out birds to knocking out power to biting people and pets, the invasive reptile has taken a toll on the island.

But a short boat ride away, birds could be found on Cocos.

In 2010, the Guam rail, or ko’ko’, was introduced there. Breeding efforts were successful, and in August 2019, the bird was reclassified from “extinct in the wild” to “critically endangered.” Only one other bird, the California condor, had been similarly reclassified.

Just a few months later, in January 2020, scientists found a snake skin on Cocos, and in September of the same year, fishers found several snakes and alerted the Department of Agriculture.

In November 2020, the U.S. Geological Survey issued a news release announcing that an invasive snake population was established on the island.

That didn't sit well with Martin Kastner and Olympia Terral.

Kastner, currently a PhD student at Virginia Tech, and Terral, a science communicator at the University of Guam, are both self-described bird lovers.

"As soon as I heard about it, I thought we should be out there looking," Kastner said.

Terral said she wasn't aware of the situation until January 2021.

"And then I just felt this urgency, like, oh my God, there's snakes out there. And then there's the ko'ko' bird, and the sali, and those birds are defenseless against a snake. And somebody has to get out there and get those snakes out of there," she said.

"And then I thought - a volunteer effort. I'm sure I could get people who really want to go out there because I really wanted to go out there. And sure enough, there was Martin."

Kastner and Terral approached the Guam Department of Agriculture separately, and they were quickly introduced. As government officials mulled over a response to the snake problem, the two bird lovers insisted on taking action themselves.

"Before we left, we were just in the parking lot talking," Terral said. "He was like, 'Yeah, I can't sleep at night, thinking about those birds."

Olympia Terral, right, instructs a group of volunteers with Friends of Islan Dano on how to effectively coordinate once they spot a snake. Photo by Dana Williams

Although the resort that once drew human visitors to Cocos has been abandoned since the pandemic, the island offers luxurious accommodations for brown tree snakes – they can eat, mate and thrive with no natural predators.

An abundance of food is available. In addition to the ko'ko', the island is home to the sali (Micronesian starlings), fahang (brown noddy), chunge (white terns), the migratory black noddy and migratory shore birds. Oceanic geckos, which are no longer found on Guam, and the endangered Mariana skink also live on the island.

The birds, asleep at night, are easy prey for the nocturnal snakes.

Kastner and Terral obtained permission from the property owner to conduct the snake removal and started a GoFundMe campaign to pay for initial boat trips to the island. In June 2021, the hunting began.

"When we first started, we had broomsticks," Terral said. Volunteers used a ladder to reach snakes that were higher off the ground.

Today, they have a well-practiced routine involving airsoft rifles and 24-foot extension poles. The Department of Agriculture has provided funding for the equipment and boat trips through the end of September.


Unlike on Guam, where food is scarce and the arboreal snakes can be found prowling on the ground, the snakes on Cocos generally stay high in the trees. They aren't interested in bait in traps – they dine on fresh, live food.

Before a large group of volunteers set out on a hunt Aug. 5, Terral delivered a briefing.

She explained how to spot snakes by their yellow bellies.

"You want to make a plan before you start to go for the snake. Because once you start to go for the snake, they're going to take off. And we take all prisoners," she said. "We don't allow any snakes to escape."

The snakes are not startled by noise, she explained, so the searchers can call out to one another.

Coordination is key. In the nighttime tangle of brown and yellow vines twisting into a thick jungle canopy, a brown and yellow snake can easily disappear.

"Once somebody spots that snake, there has to be at least two people that keep their eye on the snake, OK?" It is critical that they communicate the snake's movements to others who are getting equipment ready.

The searchers divide into small teams, using powerful lights to inspect tree branches. To facilitate the snake hunt without further jeopardizing wildlife, the island has been divided into a grid. Hand-pruned paths with reflective markers connect larger walkways and trails.

Biologist Jack Christie caught this young brown tree snake in mid-air July 22 after it was knocked from a branch. Photo by Dana Williams

On another hunt July 22, we approached a rock wall surrounded by thick tangles of vegetation.

"This is a snaky area," Terral said.

Minutes later, a voice rang out, "Snake!"

High above us, barely visible, a slender snake slithered across a branch.

The team circled the area, determined not to let the snake get away. After being shot with an airsoft pellet and coaxed from the branch with a pole, the snake was in human hands.

Because it was injured by the pellet, it was quickly dispatched to the field.

After the excitement of the catch, teams regrouped and began searching again.

Coconut crabs and geckos are common sights in the trees. As I walked down the trail talking to the searchers, I looked up to my right and saw a gecko move on a branch.

The gecko had a really long body. And no legs.

"There's one," I said.

The hunters gathered around and knocked the young snake from the branch. Biologist Jack Christie caught it mid-air.

All catches are documented – the height, the type of tree, the nearest grid marker – and the snakes are turned over to researchers. The two snakes captured that night, both females, were the 36th and 37th removed from the island by the volunteers.

The hunts organized by Friends of Islan Dano are just one part of a larger Cocos snake eradication plan encompassing efforts by local and federal agencies. Altogether, more than 100 snakes have been taken off the island.


Typically, government agencies have led the fight against the brown tree snake, but the solutions haven't always come as quickly as the community would like.

In fact, 50 years ago, some government of Guam officials were rooting for the snake.

Because the snake lives in trees and is active at night, it didn't garner a lot of attention during their first 20 years or so on Guam. Although early news accounts sometimes referred to the snake by its scientific name, Boiga irregularis, it was commonly – and erroneously – known as the Philippine rat snake.

Sen. James Butler introduced a bill in the 11th Guam Legislature that would have offered a $5 bounty on any venomous snake caught on the island. But the bill was opposed by GovGuam agencies, because the snake was believed to be beneficial.

According to an account in the March 8, 1971, Pacific Daily News, pro-snake testimony from a Department of Agriculture representative was followed by Department of Education Science Consultant James B. Branch.

Branch said the Department of Agriculture, Public Health and the "scientific community" did not view the snakes as dangerous pests, but saw them as a possible solution to the island's rat problem.

"The only natural control is the Philippine rat snake," Branch said. "If anything, we should impose a fine for destroying it."

As the years went on, the snake was blamed for frequent power outages, and people were losing hens, eggs and pets to the predators.

After community complaints about the snake increased, the Department of Agriculture issued a news release stating that snake bites were only lethal to rodents, not humans.

A March 3, 1980, article in Pacific Daily News quoted then-Wildlife Section Supervisor Bob Anderson suggesting that people bothered by the snakes should catch and transplant them or kill them.

"There's really not much we can do," Anderson said in the article. "We're not equipped or funded to handle nuisance animal complaints and there is no magic snake vanishing potion."

By the time local and federal government agencies began serious snake control measures, the damage was done.


Just as the scientists and government officials of yesteryear couldn't fathom the depth of the snake problem on Guam, little is known about the situation on Cocos today.

In 2021, biologists said there were between 200 and 500 snakes on Cocos.

"I would take that population estimate with a grain of salt," Kastner said.

Calculating the population growth rate is also problematic because the snakes' reproductive biology isn't well known.

"The thing about Cocos that is really interesting is that we don't find a lot of small snakes," he said. "It does seem like there is something on Cocos that is slowing reproduction."

He suspects it could be monitor lizards eating snake eggs.

Meanwhile, the impact of the snake on the Cocos bird population is also unknown.

"The ko'ko' seems to be doing fine," he said, and the sali are breeding successfully.


"White terns we used to see in bigger numbers. We found one in the belly of a snake," he said. "It really does seem as though they've taken a hit."

More than 200 volunteers have joined the hunts. In addition to learning how to find and remove the snakes, the searchers are taught how to avoid harming other wildlife as they walk around the island. Ko'ko' nest on the ground, and the endangered Haggan (green sea turtle) nest on the beach at Cocos.

Presumably, with such a small number of snakes on such a small island, determined volunteers could make a difference.

After all, humans have hunted entire species to extinction in the past.

But staring up into the jungle canopy, looking at layer upon layer of vines, leaves and branches that block the view of the night sky, the challenge seems daunting.

What are the chances that one human will walk by one tree and gaze up at one branch at exactly the right time and recognize that the gecko is really long and has no legs?

"I think that on Cocos, with sustained effort, there is a chance we could eradicate," Kastner said. "It feels like we are making a difference. We are definitely holding the line. That's just my gut feeling."

If you would like to volunteer or make a donation to Friends of Islan Dano, contact Olympia Terral at 671-788-6300 or

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