Saving the Last Honeycreepers: Millions of Mosquitoes in Hawaii to Prevent Extinction

For the Kauaʻi ʻōʻō, the ʻula-ʻai-hāwane, and the black mamo, any help comes too late, but the still existing honeycreepers (Drepanidini) and numerous other bird species on the Hawaiian Islands can still be saved. An unusual measure could now secure the survival of the endangered species.

The problem: Avian malaria in Hawaii

The Hawaiian Islands were long isolated and developed a unique flora and fauna. However, with the arrival of humans, invasive mammals such as rats, Indian mongooses, and pigs were introduced. Mongooses, in particular, introduced to control rat populations on sugarcane plantations, proved fatal as they prey on the eggs and chicks of ground-nesting native bird species.

Today, the Hawaiian Islands are considered a hotspot for species extinction. Since settlers arrived in Hawaii, around 100 bird species have gone extinct. Of the 44 endemic bird species still existing today, 33 are considered endangered, and a third of those have not been seen for decades and are likely already extinct. A significant reason for the mass death of birds is avian malaria, transmitted by mosquitoes. The insects arrived in the 19th century with European and American ships to the archipelago.

The native birds had no natural immunity to avian malaria and often died after a single bite. Originally, the disease was confined to the lower elevations of the islands, while birds survived in higher, cooler areas. But with climate change, mosquitoes are moving to higher elevations, bringing malaria with them. The Haleakalā National Park on Maui is particularly affected, where some of the world’s rarest birds live.

The solution: Mosquitoes with Wolbachia bacteria

To save the endangered birds, US authorities will employ an innovative method in 2024: releasing millions of mosquitoes. Each week, 250,000 male mosquitoes are dropped by helicopters onto the Hawaiian Islands; a total of ten million have already been released. These mosquitoes are infected with Wolbachia bacteria, which naturally occur in many insects and impair their reproduction. When these infected males mate with wild females, the bacteria prevent the females’ eggs from developing.

Female mosquitoes mate only once in their lives, so scientists hope the mosquito population will gradually decrease. This technique has already been successfully used in China, Mexico, and parts of the USA. Over the summer, it will become clear whether the measure is successful in Hawaii, as mosquitoes multiply intensely during this time. 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, working under the banner Birds, Not Mosquitoes.

The situation on Kauaʻi: Last-minute rescue?

On the island of Kauaʻi, this measure might be too late to secure the survival of the ʻakikiki or Kauaʻi Creeper (Oreomystis bairdi). As of 2024, only a single ʻakikiki remains in the wild, meaning the species is practically extinct in nature. According to current information, there may still be three ʻakikiki left in the wild; the species is therefore considered functionally extinct.

A few years ago, a small population was established in captivity. The population of this species shrank from 450 individuals in 2018 to only five in 2023, paralleling the spread of malaria mosquitoes on the island. Breeding individuals can only be released again once a remedy for malaria is found or the mosquito population can be reduced.

There are many other bird species on Hawaii that have become rare due to avian malaria: The ʻākohekohe or crested honeycreeper (Palmeria dolei), for example, which was already considered extinct and was rediscovered in 1945, has been severely decimated by the introduction of the disease in the mid-19th century. The highly endangered ʻiʻiwi (Drepanis coccinea) is also now limited to a very small, highly fragmented range in the higher elevations of the Mauna Kea and Mauna Loa volcanoes, primarily because of the spread of mosquitoes to lower elevations.

Why Wolbachia mosquitoes and not pesticides?

The use of Wolbachia-infected mosquitoes is preferred for several reasons. Pesticides often have far-reaching negative impacts on other species and the entire ecosystem. In contrast, using Wolbachia bacteria provides a biological method that specifically affects mosquito reproduction without harming other insects or animals.

Dr. Nigel Beebe of the University of Queensland, who has researched the Wolbachia technique on other mosquito species, explains to The Guardian: “It’s much better than using pesticides that have large non-target effects. Especially for things like conservation of critical species.” In the long term, completely eradicating mosquitoes is a challenge, particularly on the mainland. Islands are ideal for such measures because mosquito migration rates are low.

Hope for Hawaii and Its Endemic Birdlife

The updated IUCN Red List for 2024 shows both worrying developments and hopeful successes in conservation. While many species are under pressure from human activities and environmental changes, conservation projects like the one in Hawaii prove that targeted measures can lead to population recovery. Collaboration between various organizations and public support are crucial to preventing these species from becoming extinct.