By Diane Toomey
22 September 2016
(Yale Environment 360) – The few remaining species of native forest birds left on the Hawaiian island of Kauai have suffered population declines so severe – 98 percent in one case – that some are near extinction. The cause of the collapse, according to a recent study in the journal Science Advances, is not alien plants or predators, but rather warming temperatures that have enabled non-native mosquitoes carrying deadly avian malaria to invade the birds' high-elevation strongholds.
In an interview with Yale Environment 360, Eben Paxton, ecologist with U.S. Geological Survey and lead author of the study, says his group's research showed that the mosquitoes moved into the Alakai Plateau over the last decade, infecting the birds and pushing their populations to a tipping point. “We're at the 11th hour,” he says.
Paxton cites a number of approaches for eradicating the mosquitoes, including releasing irradiated infertile males, altering the bacteria naturally found in these insects, and even using genetically modified mosquitoes. As he sees it, more than the birds of Kauai are at stake. “The way that we view Kauai is that it's an early warning system for the rest of the islands,” he says. “If we get it right on Kauai then, I feel pretty good about the prospects of some of the other islands.”
Yale Environment 360: You looked at the population trends for seven species of native forest birds by comparing the results of surveys done on the Alakai Plateau. You discovered a rather dramatic population decline in all six species of Hawaiian honeycreepers. What were your findings?
Eben Paxton: What we've seen from going back to the 1980s is a gradual decline of forest birds. But it's really accelerated in the last 10 to 12 years. From 2000 to 2012, we've seen a 64 percent decline in the core range of the birds and a 94 percent decline in much of the outer portions of their range. A number of these species now exist in very small core parts of their habitat in the interior of this mountain forest.
e360: You name avian malaria, which is transmitted by non-native mosquitoes, as the main culprit here and say the rise in its incidence is due to climate change. What's been the warming trend at these higher elevations on Kauai?
Paxton: There's a really strong relationship between temperature and the distribution of disease. These high elevation forests are too cool most of the time for diseases to develop. Global warming is allowing these mosquitoes to move further up in elevation. [more]
ABSTRACT: The viability of many species has been jeopardized by numerous negative factors over the centuries, but climate change is predicted to accelerate and increase the pressure of many of these threats, leading to extinctions. The Hawaiian honeycreepers, famous for their spectacular adaptive radiation, are predicted to experience negative responses to climate change, given their susceptibility to introduced disease, the strong linkage of disease distribution to climatic conditions, and their current distribution. We document the rapid collapse of the native avifauna on the island of Kaua‘i that corresponds to changes in climate and disease prevalence. Although multiple factors may be pressuring the community, we suggest that a tipping point has been crossed in which temperatures in forest habitats at high elevations have reached a threshold that facilitates the development of avian malaria and its vector throughout these species’ ranges. Continued incursion of invasive weeds and non-native avian competitors may be facilitated by climate change and could also contribute to declines. If current rates of decline continue, we predict multiple extinctions in the coming decades. Kaua‘i represents an early warning for the forest bird communities on the Maui and Hawai‘i islands, as well as other species around the world that are trapped within a climatic space that is rapidly disappearing.