Hawaii Island’s endemic bird populations have been pressured for centuries because of disease, habitat loss, predation and loss of prey.
Hawaii Island’s endemic bird populations have been pressured for centuries because of disease, habitat loss, predation and loss of prey.
Recent work by biologists at the United States Geologic Survey Pacific Island Ecosystem Research Center indicates climate change also could threaten the populations as rising temperatures create conditions that allow mosquitoes — vectors for avian malaria and avian pox — to thrive at previously inaccessible elevations.
The pattern already has been observed on Kauai’s Alakai Plateau, where populations of two native honeycreepers, the akikiki and akekee, have declined as temperature increases and changes in rainfall and stream-flow patterns created prime habitat for mosquitoes.
Avian malaria, an introduced disease particularly devastating to the Hawaiian honeycreepers, is caused by protozoan parasites and transmitted by the southern house mosquito (also an introduced species). Pox is a virus that creates lesions on the bird’s feet and in its mouth. It likely was introduced in the 1820s.
Dennis LaPointe, a USGS research biologist, said Friday that the Kauai findings were “a wake-up call,” indicating the effects of climate change were being observed sooner than expected.
LaPointe and fellow USGS research biologist Carter Atkinson, both of whom have studied avian disease in Hawaii for more than 20 years, were authors of a paper published this summer that used epidemiological modeling to predict how certain honeycreeper populations — amakihi, apapane and iiwi — would be impacted by warming temperatures and wetter environments.
Birds such as the iiwi, a honeycreeper that lives at high elevations and thus is not often exposed to mosquitoes or the diseases they carry, are most susceptible to the changes. The iiwi demonstrates a 90 percent malaria mortality rate after exposure to one infected mosquito bite.
But when temperatures warm, the range of the mosquito broadens, pushing into higher elevations.
The summer modeling study found the impact of climate change was less pronounced at mid- and low-elevation forests, but still would cause population declines in all three species.
Still, the Big Island also has been the site for two more encouraging findings regarding avian disease. Populations of amakihi have been found in Puna that are increasing in number despite the birds being infected by malaria — a sign that the birds were gaining resistance to the disease’s effects.
“Apapane and amakihi are the two that seem to adapt,” Atkinson said. Birds with chronic avian malaria are still reservoirs for the disease, however.
Research set to be published next month relies on a comparison of disease prevalence at Hakalau Forest National Wildlife Refuge in the 1990s, when Carter and Atkinson first began their research, to prevalence between 2011 and 2013. Bird populations have increased in the refuge and disease prevalence has fallen.
This might the result of Hakalau being drier and cooler than it was in the 1990s, Atkinson said. The ongoing forest restoration work also plays a role, as damage done by feral pigs that creates breeding grounds for mosquitoes is repaired.
“We have a good understanding of the ecology of the diseases,” LaPointe said. Future projects will focus more on managing pox and malaria, particularly via control of their vectors: the mosquitoes.
Even as researchers work to understand the diseases that have established a presence on the islands, new arrivals continue to challenge the biologists. In 2007, knemidokoptic mange, a skin disease caused by the Knemidokoptes jamaicensis mite, was observed in amakihi populations.
LaPointe remembered Jackie Gaudioso-Levita, a USGS researcher who first noticed the mange on amakihi when she was a graduate student, describing the lesions as resembling “tempura batter.” The lesions can cause deformities on bird feet.
So far the mange only has been found in amakihi. How it will ultimately impact that population is still unknown, as is its source.
“It was introduced, but we don’t know when or on what,” LaPointe said.
Email Ivy Ashe at iashe@hawaiitribune-herald.com.