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Some Good News Amid Bad News, for Hawai`i’s Endangered Honeycreepers

January 30, 2014
Warming temperatures due to climate change are exposing endangered Hawaiian forest birds to greater risk of avian malaria. But new research led by the U.S. Geological Survey holds out some hope that the birds may be able to adapt.

HAWAI’I ISLAND, Hawai’i —Warming temperatures due to climate change are exposing endangered Hawaiian forest birds to greater risk of avian malaria. But new research led by the U.S. Geological Survey holds out some hope that the birds may be able to adapt. 

Image: Amakihi Honeycreeper
During the past decade populations of this honeycreeper have begun to rebound at lower elevations on most of the main Hawaiian Islands, in spite of high prevalence of infection with avian malaria. Natural selection for resistance to avian malaria is the leading explanation for this rebound and recent genetic studies indicate that these populations are genetically distinct from their higher elevation counterparts. Public domain

For decades, scientists have documented declines and extinctions among species of Hawaiian honeycreepers due to the spread of avian malaria and other diseases. At one time, the Hawaiian Islands had no mosquitoes—and no mosquito-borne diseases. But, by the late 1800s, mosquitoes were firmly established in the islands. Another invasive species—feral pigs—helped the mosquito population boom by creating larval habitat as they rooted through forests. The honeycreepers had no natural defense against a disease they had never before experienced.

"Honeycreepers are exquisitely sensitive to avian malaria," said Dr. Carter Atkinson, a USGS microbiologist based at the USGS Pacific Islands Ecosystems Research Center in Hawai’i. Atkinson is the lead author of two new research papers examining how climate change is increasing the honeycreepers’ risk of infection.

One paper, accepted for publication by the journal Global Change Biology, confirms the bad news that infection has doubled in the last 20 years among birds in one of the last high elevation refuges in the Hawaiian Islands. Atkinson and his colleagues compared data collected from birds at three sites on the remote, rugged `Alakai Plateau of Kaua`i during 1994-1997 and 2007-2013. The most disturbing result was found at the highest elevation site, where malarial infection increased from 2.0 percent to 19.3 percent.

"These increases in infection appear to be driven by a combination of environmental factors,” said Atkinson. “Warming temperatures, decreased precipitation, and changes in streamflow may be allowing mosquitoes and disease transmission to invade the highest reaches of the Plateau."

The other paper, published in EcoHealth, provides a glimmer of good news. Atkinson and his colleagues found that a rapidly expanding, low elevation population of a honeycreeper species, the Hawai’i‘Amakihi, on the island of Hawai’i has developed a tolerance for the disease.

In this study, Atkinson and his research team captured birds from both the low elevation population and from a higher elevation site. The birds were screened to ensure that they were not infected with avian malaria, and then assigned to experimental or control groups. Birds in the experimental group were exposed to malarial infection, while birds in the control group were not.

Results showed that the low elevation ‘Amakihi were able to tolerate infection much better than birds from higher elevation. Mortality rates were lower, and the low elevation birds lost less weight and maintained normal food consumption. 

But why?

"That's the next step," said Atkinson. "The emergence of this population provides an exceptional opportunity for determining the physiological mechanisms and genetic markers associated with malaria tolerance. Adaptation may be the best long-term hope for recovery for many of these species."

Image: An Endangered Honeycreeper, the `Akeke`e (Kauai Akepa), in Hawaii
Many species of Hawaiian honeycreepers have persisted into the 20th century because high elevation rain forests on the islands of Kaua’i, Maui, and Hawai’i are cool enough to limit transmission of introduced avian malaria (Plasmodium relictum). Malaria transmission is tied closely to the effects of temperature on development of malarial parasites within their mosquito vectors and the effects of temperature and rainfall on seasonal and altitudinal changes in mosquito populations. As a result, this system may be very sensitive to recently documented increases in mean temperature in the Hawaiian Islands. USGS scientists have documented recent dramatic increases in avian malaria on the Alaka'i plateau on Kaua'i that could affect recovery of two endangered honeycreepers, the 'Akikiki (Oreomystis bairdi) and 'Akeke'e (Kauai Akepa, Loxops caeruleirostris), and one endangered thrush, the Puaiohi (Small Kauai Thrush, Myadestes palmeri).     Public domain

 

Image: An Endangered Honeycreeper, the `Akikiki (Kaua`i Creeper), in Hawaii
Many species of Hawaiian honeycreepers have persisted into the 20th century because high elevation rain forests on the islands of Kaua’i, Maui, and Hawai’i are cool enough to limit transmission of introduced avian malaria (Plasmodium relictum). Malaria transmission is tied closely to the effects of temperature on development of malarial parasites within their mosquito vectors and the effects of temperature and rainfall on seasonal and altitudinal changes in mosquito populations. As a result, this system may be very sensitive to recently documented increases in mean temperature in the Hawaiian Islands. USGS scientists have documented recent dramatic increases in avian malaria on the Alaka'i plateau on Kaua'i that could affect recovery of two endangered honeycreepers, the 'Akikiki (Kauai Creeper, Oreomystis bairdi) and 'Akeke'e (Kauai Akepa, Loxops caeruleirostris), and one endangered thrush, the Puaiohi (Small Kauai Thrush, Myadestes palmeri). Public domain
Image: Alakai Field Work
Biologists use helicopters to land in a remote bog on the 'Alakai Plateau of Kaua'i to sample forest birds for introduced avian diseases. Public domain

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