Hawaii deploys mosquitoes to save rare birds

In a last desperate attempt to save rare birds threatened with extinction, millions of mosquitoes are being dropped from helicopters in Hawaii.

The archipelago's endemic, colourful honeycreepers are dying from malaria transmitted by mosquitoes introduced in the 1800s by European and American ships. As the birds have developed no immunity to the disease, they can die from a single bite.

Thirty-three species of honeycreepers have already gone extinct, and many of the 17 remaining species are critically endangered, with fears that some could be extinct within a year if no action is taken. Conservationists are now urgently attempting to save them with an unusual strategy: releasing more mosquitoes.

Every week, a helicopter drops 250’000 male mosquitoes carrying a naturally occurring bacterium that acts as birth control over the islands of the remote archipelago. Ten million have already been released.

“The only thing that would be more tragic would be if the birds went extinct and we hadn’t tried. You can’t not try,” said Chris Warren, coordinator of the forest bird programme at Haleakalā National Park on the island of Maui.

The population of one honeycreeper, the Kauaʻi creeper or ʻakikiki, has declined from 450 in 2018 to five in 2023, and according to the National Park Service, only a single bird on the island of Kauaʻi is known to remain in the wild.

Honeycreepers have a canary-like song and an incredible diversity: each species has evolved with specialized beak shapes adapted to feeding on various foods, from snails to fruit to nectar. They are an important part of the ecosystem, as they help pollinate plants and feed on insects.

Since the birds of Hawaii did not evolve alongside avian malaria, they have very little immune defense. The scarlet honeycreeper (‚i’iwi), for example, has a 90 percent chance of dying if stung by an infected mosquito.

The remaining birds typically live at elevations above 1,200 to 1,500 meters, where mosquitoes carrying the avian malaria parasite cannot survive because it is too cold. However, as the climate warms, mosquitoes are moving to higher elevations.

The researchers are using the Incompatible Insect Technique (IIT), in which male mosquitoes are released carrying a naturally occurring bacterium that prevents the eggs of wild females they mate with from hatching.

Female mosquitoes mate only once, and this is expected to reduce the overall population over time. The bacterium, Wolbachia, is found in most insects, which can only produce viable offspring with partners carrying the same Wolbachia strain.

The technique has already been used successfully to reduce mosquito populations in China and Mexico, and programs are continuing in California and Florida. The effectiveness of this program is expected to become apparent in summer, when mosquito populations typically surge.

The project is led by a coalition of groups including the US National Park Service, the State of Hawaii, and the Maui Forest Bird Recovery Project, operating under the motto «Birds, Not Mosquitoes».

Dr. Nigel Beebe of the University of Queensland examined how the IIT technique works with other mosquito species. «It is far better than using pesticides, which have major impacts on non-target species — especially when it comes to the conservation of critical species,» he said.

He added, however, that the long-term elimination of mosquitoes poses a challenge, particularly for mainland countries. “Eradication can be difficult unless you can prevent recolonization of the landscape,” he said. “Islands are ideal for that.”