In an effort to save rare Hawaiian birds from extinction, millions of mosquitoes are being released from helicopters.
The brightly coloured, endemic honeycreeper birds are dying from malaria carried by mosquitoes, which were introduced to the islands by European and American ships in the 1800s. Lacking any immunity, these birds can die from a single bite.
Of the 50 species of honeycreeper once found in Hawaii, 33 have become extinct, and many of the 17 remaining species are critically endangered. Without intervention, some may vanish within a year. Conservationists are employing an unusual tactic: releasing more mosquitoes.
Each week, helicopters drop 250,000 male mosquitoes carrying a bacterium that acts as a form of birth control. To date, 10 million mosquitoes have been released. This approach aims to curb the mosquito population and thus reduce the spread of malaria among the birds.
“The only thing that’s more tragic is if [the birds] went extinct and we didn’t try. You can’t not try,” said Chris Warren, the forest bird programme coordinator for Haleakalā national park on the island of Maui.
The Kauaʻi creeper, or ʻakikiki, exemplifies the crisis, with its population plummeting from 450 in 2018 to just five in 2023. Only one bird is known to remain in the wild on Kauaʻi island.
Honeycreepers, known for their canary-like songs and diverse beak shapes, are vital to the ecosystem, pollinating plants and controlling insect populations. However, their lack of evolved immunity to avian malaria makes them exceptionally vulnerable. For instance, the scarlet honeycreeper (‘i’iwi) has a 90% mortality rate if bitten by an infected mosquito.
These birds typically inhabit high elevations (1,200-1,500 meters or 4,000-5,000 feet), where mosquitoes do not thrive due to the cold. However, climate change is pushing mosquitoes into higher altitudes, endangering the birds’ last refuge.
Researchers are employing the incompatible insect technique (IIT), which involves releasing male mosquitoes with Wolbachia bacteria. This bacterium prevents the eggs of wild females from hatching when they mate with the infected males. Since female mosquitoes only mate once, this method gradually reduces the mosquito population. Wolbachia is naturally found in most insects, which can only produce viable offspring with partners that have the same strain of Wolbachia.
IIT has successfully reduced mosquito populations in China and Mexico, with ongoing programs in California and Florida. The effectiveness of the Hawaiian program will be evident in the summer when mosquito populations typically surge.
The project, led by the US National Park Service, the state of Hawaii, and the Maui Forest Bird Recovery Project, operates under the banner Birds, Not Mosquitoes.
Dr. Nigel Beebe from the University of Queensland, who has studied the IIT technique, notes that long-term mosquito eradication remains a significant challenge, particularly in mainland regions.
“It’s much better than using pesticides that have large non-target effects. Especially for things like conservation of critical species,” he said.
“Eradication may be difficult unless one can prevent migration back into the landscape,” he said. “Islands are ideal for this.”
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