Mosquitoes to the Rescue! The Last-Ditch Effort to Save Kaua’i’s Endangered Birds

Other Animals

Kaua’i’s forest birds aren’t exactly easy to know. Eight remaining species live in woodlands in the middle of the Pacific Ocean, many only on this island, where threats encroach from all sides. Lisa “Cali” Crampton is one of the rare people who has become acquainted with the elusive avians after spending more than a decade hiking through unforgiving terrain to study them.

Ask which is her favorite, and she names ‘Anianiau, a bright yellow honeycreeper that weighs less than four pennies. But all the forest birds have quirks. “They’re entirely charming and fascinating birds,” she says. ‘Apapane and ‘I’iwi are crimson red, nectar-drinking honeycreepers, the former distinguishable by its “white underpants,” she says, and the latter by a striking curved bill. The endangered ‘Akeke’e pries open leaf and flower buds with a unique cross-tipped beak. And acrobatic ‘Akikiki are just as likely to perch upside-down on a branch as right-side up. “You can’t underestimate their spiritual and cultural value,” Crampton says. “These birds have always had Hawaiian names.”

Treasured as the birds are, several species are also in serious trouble. Three live only on Kaua’i and are critically endangered, including ‘Akeke’e and ‘Akikiki, with estimated populations of less than 1,000 and 500 individuals, respectively. Four other species were deemed extinct by the last month. The same forces that spurred their declines, including deforestation, invasive predators, and introduced mosquitoes carrying disease, have already driven many of Kaua’i’s forest birds to extinction in the past 50 years. While the forests once held at least 13 different species, today only eight remain, and several are critically endangered.


Elsewhere, birds evolved alongside native mosquitoes and developed some immunity to avian pox and avian malaria. But until humans inadvertently introduced the insects to the atoll in the 19th century, Hawaiian birds lived in a mosquito-free environment. They have no innate defenses against the pests. Unable to fend off disease, the birds retreated to mountainside areas too cold for the mosquitoes’ survival. Now even that haven is threatened: Climate change has brought warmer temperatures, allowing mosquitoes to expand upslope into habitats once cool enough to keep the birds safe. Crampton, leader of the Kaua’i Forest Bird Recovery Project, is focused on combatting mosquitoes, and she’s employing a powerful weapon to rid Kaua’i of these pests: bacterial birth control, an approach that manipulates the mosquitoes’ gut bacteria to cause their population to crash.

The Alaka'i Plateau in Kaua'i's northwest highlands is the last remaining place where three critically endangered birds—Puaiohi, Akikiki, and Akeke'e—still survive. It was also the last place where five birds—Kama’o, Kauai O’o, O’u, Kauai Nukupu’u, and Kauai Akialoa—held out before their extinction during the twentieth century. Photo: Universal Images Group North America LLC/Alamy
The Alaka’i Plateau in Kaua’i’s northwest highlands is the last remaining place where three critically endangered birds—Puaiohi, Akikiki, and Akeke’e—still survive. It was also the last place where five birds—Kama’o, Kauai O’o, O’u, Kauai Nukupu’u, and Kauai Akialoa—held out before their extinction during the twentieth century. Photo: Universal Images Group North America LLC/Alamy

Of the six invasive mosquitoes on Hawaii, Crampton is most interested in Culex quinquefasciatus, a nocturnal bug known as the southern house mosquito that’s been here since 1826 and acts as a vector for avian malaria and avian pox. Both diseases weaken and kill endangered ‘Akikiki and Akeke’e. The first step to squashing their populations, somewhat ironically, is producing more of the blood-suckers.

“They stink, I’m warning you,” Crampton says as she places a black mosquito trap on her office desk in Hanapepe, Kaua’i. She flips a switch and a battery-powered fan blows air laced with carbon dioxide and a dank smell approximating a locker room. When she sets the trap in the field, female mosquitoes seeking a blood meal approach and it sucks them inside. Crampton then transports her quarry to her lab, where she breeds them. She inoculates the males with a strain of gut bacteria that effectively sterilizes them: If those male mosquitoes mate with wild females, the resulting eggs never hatch.

If scientists can release enough lab-altered males to overwhelm the wild ones, they could dramatically reduce the bugs’ population—and protect birds from mosquito-borne diseases.

Mosquitoes and other insects under a microscope in Crampton's lab. The mosquito's sophisticated proboscis pierces skin and finds blood vessels to drink from, inadvertently introducing disease directly into birds' bloodstreams. Photo: Bryn Webber
Mosquitoes and other insects under a microscope in Crampton’s lab. The mosquito’s sophisticated proboscis pierces skin and finds blood vessels to drink from, inadvertently introducing disease directly into birds’ bloodstreams. Photo: Bryn Webber

It’s a time-intensive measure, and it falls under the umbrella of “biocontrol”—a controversial practice wherein new species are introduced to an ecosystem in hopes that they can control established invasives. Crampton and others know how spectacularly such measures have failed in the past; thus they’re approaching their project with extreme caution. Yet they feel like such a dramatic strike might be the only option to give the birds a fighting chance.

Intentionally and inintentionally, humans have ferried non-native species around the world for as long as we’ve traveled. But in the 1800s, the experimental practice of biocontrol set new standards for importing invasive species, often with disastrous results. In 1883, owners of sugar cane plantations in Hawaii introduced mongoose to the islands of Maui, Moloka’i, and O’ahu to control rats. They failed to realize that not only are diurnal mongoose asleep while nocturnal rats are active, but also that mongoose eat insects, birds, eggs, and plants—notably, not rats. Today, mongoose continue to prey on Hawaii’s endangered birds and cause millions of dollars in damages annually. Fortunately they’re not present on Kaua’i.

Scientists and wildlife workers today have absorbed this and other disastrous lessons of the past.

Scientists and wildlife workers today have absorbed this and other disastrous lessons. They still experiment with biocontrol, but typically undertake stringent testing before releasing any organisms to the wild, especially predators that could have ecosystem-wide impacts.

Take the hemlock woolly adelgid. The sap-drinking insect, native to Asia, has no natural predators in the Eastern United States, giving it free range to devastate hemlock forests and drive declines in avian inhabitants like and Hermit Thrush. To restore hemlocks, government scientists tested whether releasing two insect-eating beetle species from British Columbia would cause any unintended consequences. After they proved that both beetles preyed on hemlock woolly adelgids without causing problems for native bugs, they let loose thousands of them, starting with Japanese ladybeetles in 1995 and then Laricobius nigrinus in 2003. But so far, the invaders’ populations haven’t become established enough to crush the adelgids and save the trees.

University of Minnesota entomologist George Heimpel is taking a more targeted approach to exterminate an invasive fly that poses one of the greatest threats to Galápagos birds. Philornis downsi, which arrived to the islands in the 1960s, parasitizes at least 18 endemic and native bird species. Fly larvae creep into the nostrils of defenseless baby birds, including the native Galapagos Finch, and chew away at their nasal lining, killing chicks or leaving them with deformed beaks. Heimpel’s team has identified two wasp species that parasitize Philornis downsi exclusively, which they predict will protect the Galápagos’ native insects from potential side effects. “If we do our work right, it won’t be killing other organisms,” says Hempel, who has not yet released the wasps.

Mosquito traps placed in Kaua'i's forest attract female mosquitos. Once captured, Crampton breeds them in the lab to ultimately produce and release a strain of the insects altered to sterilize the island's mosquito population. Photo: Bryn Webber
Mosquito traps placed in Kaua’i’s forest attract female mosquitos. Once captured, Crampton breeds them in the lab to ultimately produce and release a strain of the insects altered to sterilize the island’s mosquito population. Photo: Bryn Webber

Crampton’s approach to controlling Kaua’i’s mosquitoes goes fully microscopic. Instead of targeting Culex quinquefasciatus itself, she plans to modify the insects’ gut bacteria. These mosquitoes, and as many as 65 percent of all terrestrial insect species, carry strains of a bacteria called Wolbachia. By modifying the specific strain of Wolbachia in lab-raised Culex males so that it’s different than the Wolbachia carried by wild female mosquitoes, the couples will produce infertile eggs. Over time, this should reduce the overall mosquito population on Kaua’i, and, if it works, also the rate of avian disease. The end goal is to reduce the mosquito population enough that the endangered birds will be safe from disease and make a comeback.

This Wolbachia method is already in use in the United States, for example in Miami, to bring down Aedes aegypti mosquito populations that transmit disease to humans. Because Aedes mosquitoes don’t carry Wolbachia, scientists simply expose the bugs to the bacteria; the male-female mismatch results in infertile eggs. In 2018 scientists released more than 6.8 million Wolbachia-infected males over a six-month period across a 150-acre area of the city, hoping that reduced mosquito populations would lead to fewer cases of Zika. A follow-up study showed a 75 percent reduction in area Aedes aegypti mosquitoes because eggs failed to hatch.

If Crampton released altered mosquitoes in Kaua’i, it would be the first time the Wolbachia technique is used for avian conservation. Scientists are optimistic it could work without causing unintentional harm to other species.

“It’s not the sort of traditional biocontrol where you release a specific organism to target another organism,” says Eben Paxton, a U.S. Geological Survey ecologist in Hawaii who is currently working on an avian malaria genome project. “It seems to be the least risky in terms of anything unintended going wrong.”

It will be years before any mosquitoes are released. Crampton now has the mosquitoes back in Kaua’i after a Michigan-based collaborator infected them with Wolbachia. But there are still regulatory hurdles to clear, including environmental assessments and public hearings. “If everything went smoothly, maybe we could do field trials in one to two years and then actual full-on landscape release in three to four years,” says Teya Penniman, who coordinates the Hawai’i Landscape-scale Mosquito Project at the non-profit American Bird Conservancy. They don’t yet know how many mosquitoes they’d have to release to overwhelm the wild population with Wolbachia birth control.

Dr. Crampton holds a Kauaʻi ‘Amakihi. She has spearheaded the bold effort to reduce Kaua'i's mosquito populations. Photo: Courtesy of Lisa “Cali” Crampton
Dr. Crampton holds a Kauaʻi ‘Amakihi. She has spearheaded the bold effort to reduce Kaua’i’s mosquito populations. Photo: Courtesy of Lisa “Cali” Crampton

Crampton is not relying solely on this biocontrol strategy to save the birds. This year the team began dosing forest streams with bacteria called BTI (Bacillus thuringiensis israelensis), which kill mosquito larvae; outside of also killing a few midge species, BTI has no other known ecological impacts. It’s a short-term fix at best, since it only targets mosquitoes in small, localized areas. The Wolbachia approach, on the other hand, would sterilize mosquito eggs across the entire forest. But Crampton says that they can’t sit by until the biocontrol route is approved; the most endangered birds might not have a couple years left.

“We’re doing emergency meetings this month with all the partners across the state that can influence forest-bird conservation to determine if we need to take more aggressive measures,” Crampton says. They could launch captive-rearing programs for ‘Akikiki and Akeke’e, or relocate some birds to the island of Hawai’i where mosquitoes are less of a problem.

“It has been rough watching these birds decline, but we cannot give up,” she says. “Not taking action is a choice, too.”

Before I leave Kaua’i, Crampton directs me to a trail that will take me into the Alakai Swamp so I can see some of her beloved birds myself. The sun is out when I arrive at one of the wettest places on the planet, which has an average annual rainfall of 200 inches. The rich, red earth forming the path includes inclines so steep, I have to crawl with my hands. Years of heavy rainfall have produced deep grooves around the clay. After two miles of hike-scrambling, the dirt transitions into a boardwalk—and that’s when I hear birdsong. Feathered brown heads peek out from the trees—they’re Kaua’i Elepaio, the most numerous of the island’s songbirds.

None of the three endangered species show themselves to me, but as I’m leaving the swamp a red dart shoots by. Maybe it’s an ‘Apapane or I’iwi, two dazzling honeycreeper species, both declining in number. Seeing it, I understand better why Crampton has dedicated herself to a battle that may only ever be a stalemate. Even if she manages to rid Kaua’i of mosquitoes, she’ll still have to contend with rats and and invasive plants and climate change. But if they can reduce this one threat and finally reduce the mosquito populations, it may be enough of an opening for the forest birds to make a comeback.

This article by Lorraine Boissoneault was first published by Audubon on 4 November 2021. Lead Image: Today only eight forest bird species (all pictured here) survive on Kaua’i; at least five other species have been driven extinct. A novel biocontrol technique would try to take down invasive mosquitoes, which spread diseases killing birds, including several critically endangered species. Photos clockwise from top left: Kauaʻi ‘Amakihi, Photo Resource Hawaii/Alamy; Puaiohi, All Canada Photos/Alamy; ‘Apapane, Michael Greenfelder/Alamy; ‘Akikiki, Justin Hite; Kauaʻi ‘Elepaio, Mitch Walters/Audubon Photography Awards; ‘Akeke‘e, C. Robby Kohley; ‘Anianiau, Photo Resource Hawaii/Alamy; ‘I’iwi, Joshua Pelta Heller/Audubon Photography Awards.


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