It’s hard to imagine a time when Hawaii’s native forest birds were so abundant that Hawaiian honeycreeper songs were ear-splitting, as one early naturalist described it.

Only 17 forest bird species are left in the islands, down from more than 50 that evolved here over thousands of years, according to the Audubon Society. And nearly all of those that persist appear poised for extinction in this century as threats to their survival intensify with the onset of climate change.

Over time, Hawaii’s mountaintop forests have become the birds’ last refuge. That’s because this high-elevation habitat has historically been too cool to host the birds’ most severe threat: mosquitoes carrying avian malaria.

But as climate change drives up temperatures in Hawaii’s mountaintop forests, mosquitoes are moving toward the summit, threatening to banish the birds’ only disease-free frontier.

This kiwikiu was one of 13 endangered Maui parrotbills that were recently moved from one side of Haleakala to the other in an effort to establish an “insurance population” to prevent extinction. Mosquitoes killed all but one of the birds by infecting them with avian malaria. Courtesy: Bret Nainoa Mossman/MFBRP

Hope is on the horizon. Scientists this year launched an ambitious project to create a new conservation tool that would control mosquitoes in the birds’ habitat by inhibiting their ability to produce fertile offspring, setting into motion something that’s been discussed by researchers for decades.

The multi-agency effort marks a historic first attempt at landscape-scale mosquito control in Hawaii. If it works, and if it can be implemented quickly, the birds might get a much-needed lifeline. But regulatory hurdles remain and supporters say community buy-in is essential. 

“These birds are unique and precious and found nowhere else in the world,” said Chris Farmer, American Bird Conservancy’s Hawaii program director. “They’re an integral part of Hawaii’s biological and cultural heritage. If they disappear, the legacy of extinction will continue.”

Welsh artist Ralph Steadman depicted this mosquito as part of an effort to raise awareness for endangered species. Courtesy: Ralph Steadman

Conservationists worry mosquito-borne disease could wipe out the last of Hawaii’s defenseless forest birds within decades. Some species, like the kiwikiu on Maui, have even less time. Biologists estimate only about 150 kiwikiu, or Maui parrotbills, are left in the wild, making them next in line for extinction.

Mosquitoes are thwarting recovery efforts. In October, a dozen kiwikiu were moved from their last stronghold on the windward slopes of Haleakala to the other side of the mountain where they likely once lived.

But all but one bird has died after being bitten by mosquitoes carrying avian malaria. Scientists had not detected the presence of mosquitoes on previous surveys but suspect a record hot summer played a role in making it possible for the bugs to reach such high altitudes.

“Saving these species in the wild will be hopeless in the long term unless we have disease control,” said Hanna Mounce, coordinator of the Maui Forest Bird Recovery Project.

Mosquitoes appeared in Hawaii in the early 1800s with the arrival of European cargo ships. The Southern house mosquito, which now threatens the birds with avian malaria, came in water barrels drained by sailors on Maui in 1826. Other mosquito species, like the Asian tiger mosquito and yellow fever mosquito, showed up on Hawaiian shores at the turn of the 19th century, according to a 2017 report by scientists working on solutions for a mosquito-free Hawaii. 

We brought mosquitoes to Hawaii so it’s our kuleana to fix it.” — Lisa “Cali” Crampton, bird biologist

Studies going back more than half a century have identified avian malaria — and the mosquitoes that transmit it — as the biggest threat facing Hawaii’s native birds.

In 1967, biologist Richard Warner wrote a paper for the University of California, Berkeley, about how the birds were finding refuge at higher elevations because the disease-carrying mosquitoes were restricted to areas below 2,000 feet. Today, mosquitoes are reaching birds at elevations three times higher and solutions still remain years away from implementation.

In the last half-century, disease-carrying mosquitoes helped wipe out several Hawaiian forest bird species. 

“This is one piece of the story of how humans are going to cause mass extinctions of wildlife species in this century,” said Michael Samuel, a wildlife disease ecologist at the University of Wisconsin, who has studied Hawaii’s forest birds for two decades.

There are other dangers. Before mosquitoes arrived on the scene, numerous forest bird species were lost to the mouths of hungry rats. Habitat loss, competition from invasive species and predation by non-native animals like feral cats have also brought down the birds’ numbers.

Conservationists make steady efforts to combat these threats with fencing, invasive plant removal and small mammal traps. But scientists agree that extinction prevention is unlikely to succeed without the development of new tools to fight avian disease. 

Birth Control For Mosquitoes

Here’s the plan: Scientists want to collect wild Southern house mosquitoes from the forests where the birds live and infect the bugs with a bacteria called Wolbachia. 

The Southern house mosquito, and most insects in the world, already carry one of five strains of the bacteria in their reproductive tract. But scientists are finding that if they drain the Southern house mosquito of its natural bacteria strain and infect it with a different strain sourced from another species of Hawaii mosquito, they’ll achieve a new form of mosquito birth control.

Scientists would then release into the wild a large batch of these male mosquitoes, which are infected with the different Wolbachia strain, to mate with wild females. The distinction in bacteria strains between the males and females would render their offspring sterile.

apapane, mosquito, forest birds, avian malaria
A mosquito bites the face of an apapane, a species of Hawaiian honeycreeper that is endemic to the islands. Scientists say the Apapane appears to tolerate avian malaria slightly better than other honeycreepers, which may be why it is the most abundant Hawaiian honeycreeper species. Courtesy: Jack Jefferey Photography

Since female mosquitoes mate only once, this incompatibility would send the wild mosquito population plummeting, achieving some relief for the birds.

And since male mosquitoes don’t bite, there would be no risk to the birds (and no added nuisance for humans) by releasing the batch of male mosquitoes into the birds’ mountaintop habitat. 

In addition to curtailing mosquitoes’ mating compatibility, the Wolbachia technique might also impede the insect’s ability to transmit malaria to the birds. That has been the case when the Wolbachia method has been applied in other mosquito species.

Google’s parent company, Alphabet, has a start-up in California called Verily that’s working on eradicating mosquito-borne diseases using a similar method.

The company started in Fresno a few years ago by releasing thousands of Wolbachia-infected male mosquitoes to crash the population of Aedes aegypti, a mosquito species that can carry Zika and dengue fever.

While those diseases aren’t usually transmitted in central California, they are in many other places around the world. And if this pilot test works — and early signs suggest it will — the method could help save human lives and in theory be used to help save bird lives.

There are other methods of sterilizing mosquitoes. One approach is to zap the male mosquitoes with a non-lethal dose of radiation to sterilize them and then release them back into the environment.

Another means involves modifying the genome to make the males sterile. This GMO approach is being pursued in Florida, where public health regulators are trying to control mosquitoes that transmit the Zika virus, which can cause devastating birth defects in babies whose mothers contract the virus. But it’s wildly controversial with the public despite having gained federal approvals from the Environmental Protection Agency and Food and Drug Administration.

Hawaii scientists and state land managers are steering clear of any GMO solutions.

Green pools of stagnant water in Nakula harbor mosquito larvae. These pools are at 6,000 feet elevation, normally thought to be mosquito-free. But biologists think the black rock and sun exposure may maintain warmer pools than you would expect for this elevation. Courtesy: Chris Warren/MFBRP

Instead they are pursuing the Wolbachia method, using bacteria sourced from mosquitoes already found in Hawaii, because this developing technology appears to have the best shot at winning public and regulatory approval, according to several researchers familiar with the project.

“Most people think it’s probably the best short-term solution to prevent extinction, especially for some of the rarest honeycreepers,” said Carter Atkinson, a microbiologist at the U.S. Geological Survey’s Pacific Islands Ecosystems Research Center on the Big Island.

It is not a panacea. Releasing mosquitoes infected with Wolbachia onto the landscape is expected to help control the mosquito population, not eliminate it. That’s seen as a pro and a con, though. There would be a recurring cost, but also an undo button.

To maintain this control, researchers would need to conduct these male mosquito releases in perpetuity. If the releases were to stop, the mosquito population would rebound.

In the long-term, researchers suspect this still-developing method of mosquito suppression could be rendered far less effective by an increasingly warming climate. 

As high altitudes become more suitable for mosquito reproduction, researchers might need to one day release such a large number of sterilized male mosquitoes so as to render the method untenable, Atkinson said.

“The thought is that over time, as the climate gets warmer, it could kind of overwhelm the whole system unless you keep releasing bigger and bigger batches of the sterile males,” said Atkinson, who has spent most of his career studying avian malaria. “This method will have the greatest impact early on. It would buy researchers more time to come up with something else.”

It could give the birds another half-century, which researchers hope would be enough time to come up with a lasting solution and ideally prevent another extinction.

Extinction Deadline Looms

In Hawaii’s high-elevation forests, those above 4,000 feet or so, the danger season for the birds is intensifying. 

On Kauai, it used to be that the birds would get a break from disease-carrying mosquitoes from December to July — a window of time when the climate was too cold for mosquitoes to survive. Now the mosquitoes keep out of the high-elevation forest for only about half the year. 

As the planet warms, the birds’ temporal refuge continues to shrink.

“I want people to understand that we created this problem,” said Lisa “Cali” Crampton, coordinator of the Kauai Forest Birds Recovery Project. “We brought mosquitoes to Hawaii so it’s our kuleana to fix it.”

The iconic iiwi, an endemic Hawaiian honeycreeper, secured its status on the endangered species list in 2017. Avian malaria is the primary driver in the population decline. Nathan Eagle/Civil Beat

Kauai is not a very high island compared to Maui or the Big Island, which have peaks topping 10,000 and 13,000 feet, respectively. So the increasing appearance of mosquitoes at higher elevations is happening faster on the Garden Isle, which tops out just over 5,000 feet. As a result, more native birds have been exposed to avian malaria. 

All six native honeycreeper species left on Kauai have endured dramatic declines since the late 1990s, researchers have found.

A 2016 study co-authored by Crampton makes a foreboding prediction: If akikiki didn’t go extinct by 2015 (they didn’t; there are approximately 500 left in the wild) then the species should hang on until 2050. 

But the prophecy doesn’t account for the ever-increasing prevalence of mosquitoes researchers are finding in the birds’ forest refuge as climate change continues to rattle weather norms. In the report, the birds’ rate of decline is based on mosquito prevalence that’s static.

Scientists say the birds would likely die off faster if their last refuge becomes further inundated by mosquitoes. To scuttle this course, scientists must act quickly. 

“We don’t have very much time — a decade or two at best,” Crampton said.

The alala, an endemic Hawaiian crow, has been brought to the brink of extinction thanks in large part to avian malaria. There’s an effort underway to reintroduce it in the wild at higher elevations on the Big Island. Courtesy: San Diego Zoo

She believes this is not a deadline to be missed.

“Without birds to pollinate and disperse seeds and control insects in these forests, we have no forest,” she explained. “Without the forest, we don’t have water to drink, we don’t have flood control, we don’t have the underpinnings of human existence on these islands. So saving the birds is not superficial — it’s imperative.”

Scientists say mosquito sterilization is the most feasible, but not the only way to halt avian malaria’s death march. It’s possible that the birds could evolve over time to develop a tolerance for the disease, which is something that has been documented on the Big Island with low-elevation amakihi.

But Samuel, the wildlife disease ecologist, isn’t banking on it.

These bird populations are small and lacking in genetic diversity, so the opportunity for them to develop a resistance to avian malaria is very limited, Samuel said.

Samuel contributed to a research paper that’s under peer review that unpacks whether it might be feasible to use genetic modification to develop disease-resistant birds, and if so how many birds would scientists need to release into the wild to save the species?

It’s a controversial premise. But this kind of science is already being explored in places like California, where conservationists hope to conduct the first release of a genetically altered endangered species into the wild by creating a disease-resistant black-footed ferret.

“People have gone so far as to say we should re-create dinosaurs,” Samuel said. “Then there are medical applications of this and one strategy, which is probably going to be used in the future more regularly, is to take DNA from people who have higher genetic risks of developing something like breast cancer and correcting that mutation so they wouldn’t have the disease.”

While the science and medical worlds explore the ethics and boundaries of these groundbreaking technologies, Hawaii’s forest bird researchers are moving ahead with their comparatively basic but sure-footed technique.

“It seems like mosquito control is the second-best strategy for us,” Samuel said. “The first best strategy would be for the birds to evolve some kind of tolerance or resistance, but we don’t have any control over that.”

The Test Lab

A major player in the inter-agency charge to suppress mosquitoes in Hawaiian forest bird habitat is Adam Vorsino, ecologist with the U.S. Fish and Wildlife Service. 

Feral goats and pigs create and maintain muddy pools like this one on Maui. They become breeding grounds for mosquitoes. Courtesy: Chris Warren/MFBRP

In a laboratory on Oahu, Vorsino is developing mosquito rearing techniques. Once he perfects the protocol for lighting, temperature and feeding to establish a self-sustaining population, he’ll share it with researchers at Michigan State University, where scientists have already had success using the Wolbachia method to sterilize male mosquitoes capable of spreading dengue, Zika and other diseases in China.  

In Michigan, scientists will receive shipments of mosquito eggs from Vorsino and inject the embryos with the bacteria. Then they’ll conduct a wide range of experiments to find out if the Wolbachia method works on Hawaii’s Southern house mosquito.

Although this method of mosquito population suppression has worked as a public health tool to reduce the prevalence of human malaria elsewhere in the world, it has never been used as a conservation tool nor with the mosquito species that’s spreading deadly bird diseases in Hawaii.

Vorsino’s mosquito lab on Oahu is partly supplied by insects trapped and collected by Crampton and her team of biologists on Kauai.

They use a battery-powered trap that masquerades itself as a red-blooded animal, emitting a burst of carbon dioxide and an odor reminiscent of sweaty gym socks to draw mosquitoes in closer. When a mosquito flies near the stench, a battery-powered fan sucks the insect into a downdraft and captures it.

A helicopter is required to transport Crampton and her team to the high-elevation sites where they check the traps for mosquitoes. Captured mosquitoes feed on sugar water for a couple of days until Crampton and her team package and deliver them to FedEx for shipment to Oahu.

When Vorsino received the first package of Kauai mosquitoes, not all of the insects were alive. As it turns out, mosquitoes don’t like getting jostled around in the mail.

Crampton said her team has since overcome this hurdle. 

“We actually had never really collected mosquitoes before this project,” Crampton said. “We’re bird biologists. None of us have backgrounds in working with insects so we are really learning on the fly.”

Rallying Public Support

When the world’s largest conservation organization met in Honolulu for the first time in 2016, the members passed a resolution calling on the governments of Hawaii and the United States to implement the forest bird recovery plans and seek additional resources to avoid any more extinctions. 

The International Union for the Conservation of Nature’s World Conservation Congress, which includes thousands of members, also called for expedited reviews and development of all appropriate techniques to control or eradicate invasive mosquitoes.

Early indicators suggest the Wolbachia technique may be able to suppress the mosquito population in targeted areas by up to 90%, Vorsino said. So far, this potential solution is the birds’ best chance.

kiwikiu mosquito avian malaria
This male kiwikiu was one of the endangered birds that didn’t survive long after being moved to a new higher-elevation home on Maui. All but one of the birds died from disease-carrying mosquitoes. Courtesy: Bret Nainoa Mossman/MFBRP

But it could take several years for the technology to develop, according to several researchers knowledgeable about the project. Vorsino declined to estimate when the Wolbachia method might be ready to move out of the laboratory and into the field. But several other researchers familiar with the project ventured a guess of up to five years.

Cynthia King, the entomologist at the Department of Land and Natural Resources, has convened the state mosquito working group quarterly for the past three years. She is encouraged by Michigan State’s progress but still sees implementation as very far away.

“Given everything happening now, it feels like an eternity,” she said.

Developing this conservation tool in the lab is just part of the battle. Scientists will also need to achieve public support and regulatory approval.

“We need community buy-in,” said Farmer, of the American Bird Conservancy. “This is a major management action. No one takes it lightly. But it’s one that if we don’t do it, we’re going to lose the honeycreepers.”

Part of the challenge in public perception and understanding is communicating what is actually being considered for Hawaii. In short, it’s not GMO. 

All of the organisms involved in the Wolbachia method are already found in Hawaii. For scientists working on the project, this is an important distinction. There are no foreign imports. Nothing in the insect’s genome will be manipulated.

While there are efforts outside of Hawaii to sterilize mosquitoes with genetic modification, the Wolbachia method is not one of them. 

“The worst thing that could happen is for people to get afraid of the technology and say, ‘No,’” Atkinson said. “But I think if people are educated properly about it, it’s not something that people will be afraid of. I think the public will get on board.”

More broadly, Atkinson said the birds themselves need public support.

“The disconnect between people in Hawaii and the native forest birds really hurts this because most people don’t know what an apapane is or what an amakihi is,” Atkinson said. “You’re trying to sell them on saving something they don’t understand or even know where it lives.

“It’s not like New Zealand where you have the whole country rallying around the Kiwi bird,” he added. “There’s no big group of people supporting native birds here in Hawaii.”

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