Malaria in the Mist: How a Mosquito is Emptying Hawaiian Forests
Long-term surveys reveal catastrophic losses among native Hawaiian honeycreepers as avian malaria pushes species toward extinction while introduced birds thrive
Native species in freefall
The latest 2023 survey data from the Alaka'i Plateau reveal continued and in some cases accelerated population declines in Kaua'i’s native forest birds. Most notably, the once-common 'i'iwi (Drepanis coccinea) now number as few as 47 individuals, down from over 1,500 just five years prior. 'Akeke'e (Loxops caeruleirostris) and 'anianiau (Magumma parva) also experienced steep drops, and 'akikiki (Oreomystis bairdi) went completely undetected. These trends suggest that extinction for several species may be imminent. Model projections indicate the 'i'iwi could vanish from Kaua'i by 2038, and the 'akeke'e by 2048 if current rates of decline continue.
The declines are linked closely to the spread of avian malaria, transmitted by the introduced Southern House Mosquito (Culex quinquefasciatus), which now reaches even the island's highest elevations. With a maximum height of just 1,598 m, Kaua'i may no longer provide disease-free refuges for its highland specialists. This represents a significant shift from previous decades, when upland areas still supported viable populations.
Introduced species on the rise
While native birds decline, several introduced species are increasing in both abundance and range. The Warbling White-eye (Zosterops japonicus) and Japanese Bush Warbler (Horornis diphone) have shown exponential growth, particularly in lower elevations. Their expansion into native forest habitats is altering community composition. From 2000 to 2023, the proportion of introduced bird detections in the plateau’s outer areas rose from 34% to 59%.
Not all non-native birds are thriving equally. Northern Cardinal (Cardinalis cardinalis) populations are declining, possibly due to hurricane-related habitat loss or limited food resources. However, most introduced species appear resilient and are outcompeting natives in disturbed or lowland environments. This raises concerns about whether the newcomers can adequately replace the ecological functions lost as native insectivores, nectarivores, and frugivores disappear.
Extinction forecasts signal urgency
Forecast models suggest a grim outlook. If current exponential decline rates persist, the 'i'iwi and 'akeke'e are likely to fall below viable population thresholds within 25 years. 'Anianiau and Kaua'i 'amakihi (Chlorodrepanis stejnegeri) may survive past 2050 but in dangerously low numbers. Native diversity is contracting toward the high-elevation Interior, with many species already extirpated from lower-elevation habitats.
Historically widespread species such as the Kaua'i 'amakihi have lost 79% of their population since 2000. Even more concerning is the complete absence of 'akikiki in the 2023 data. Their status now mirrors past extinctions of the Kaua'i 'o'o and the Kaua'i 'akialoa, whose populations collapsed following hurricanes and disease outbreaks.
Avian malaria the principal driver
The key threat is clear: avian malaria. Native honeycreepers, having evolved in the absence of mosquito-borne diseases, are highly susceptible. Warming temperatures have enabled mosquitoes and the Plasmodium parasite to colonise higher altitudes, eroding the last refugia for endemic birds. Even species that appeared moderately resistant, such as the 'apapane (Himatione sanguinea), show signs of stress at lower elevations.
Molecular studies reveal high parasite loads in both native and introduced birds, suggesting that both may be maintaining the disease cycle. The arrival and proliferation of disease-carrying mosquito vectors in formerly safe zones has been catastrophic for Kaua'i’s endemic birds. The relatively stable populations of 'apapane and Kaua'i 'elepaio (Chasiempis sclateri) offer limited comfort given the broader trajectory.
Conservation efforts and future hope
In response to the crisis, mosquito suppression has begun. In 2025, the Incompatible Insect Technique (IIT) was deployed on Kaua'i, involving the release of male mosquitoes carrying a different strain of Wolbachia to reduce mosquito reproduction. Captive breeding has also expanded, with plans underway for ex situ conservation of 'anianiau and continued efforts for 'akikiki and 'akeke'e.
Ongoing monitoring is critical. Although full surveys occur every five years, researchers recommend increasing the frequency or using passive acoustic monitoring to track population changes more closely. Without immediate intervention, conservationists warn that several native species will be lost within a generation - erasing not just biodiversity but vital ecological roles in pollination, insect control, and seed dispersal.
The Kaua'i forest bird community is in freefall. Its fate now hinges on the success of mosquito control, habitat protection, and the will to act before it is too late.
August 2025
Share this story
