Hawaiian Honeycreepers Losing Ground to Climate Change

The Hawaiian Islands are a fairly typical example of island biodiversity. Isolated from contact with mainland species, the islands' organisms evolved into unusual forms found nowhere else, and many species found elsewhere were not present. The rare organisms thrived, at least until humans arrived, making changes in the landscape and bringing invasive species. Many of Hawaii's endemic species are now endangered as a result.

For some of Hawaii's most iconic birds, the honeycreepers, there is a more insidious threat. Mosquitos – and mosquito-borne illnesses – are expanding their range on the islands thanks to climate change.

At one time, the Hawaiian Islands had no mosquitoes – and no mosquito-borne diseases. But, by the late 1800s, mosquitoes had set up permanent housekeeping, setting the stage for epidemic transmission of avian malaria and pox. Honeycreepers – just like people faced with novel viruses such as swine flu – had no natural resistance against these diseases.

Before long, Hawaii’s native honeycreepers significantly declined in numbers and geographic range. It was likely that malaria swept rapidly across all of the lower Hawaiian Islands after the disease was introduced, leaving few survivors. Today, native Hawaiian birds face one of the highest rates of extinction in the world. Of 41 honeycreeper species and subspecies known since historic times, 17 are probably extinct, 14 are endangered, and only 3 are in decent shape.

Since malaria transmission depends on a warmer climate, honeycreepers so far have been able to find refuge in high altitude regions. These offer suitable habitat for the birds but are inhospitably cool for mosquitos. But that may change:

Although most disease transmission now occurs in these mid-elevation forests, this will change if the projected 3.6 degrees Fahrenheit (2 degrees Centigrade) raise in temperature occurs.

“With this kind of temperature change, about 60 to 96 percent of the high-elevation disease refuges would disappear,” said Atkinson. For example, available high-elevation forest habitat in the low-risk disease zone would likely decline by nearly 60 percent at Hanawi Natural Area Reserve on Maui to as much as 96 percent at Hakalau Forest National Wildlife Refuge on Hawaii Island. On other islands, such as Kauai, with lower elevations and no low-risk zones even now, predicted temperature changes would likely be catastrophic for remaining honeycreeper species.

The extinction (or even decimation) or more honeycreepers would be a tremendous biodiversity loss for the world and perhaps an economic loss for Hawaii. Endemic species are a major draw, and for me at least, honeycreepers would be near the top of the list of species to see if I ever visit the state. I imagine other birders would feel likewise. So it is likely in the state's interest to manage habitats in such a way as to give these unique birds the best shot possible at survival. In the long run, however, only slowing or stopping climate change will put these and other rare species back into safe territory.