Climate Change May Become a Serious Threat to Kaua‘i’s Birds

By Ruby Pap

An i‘iwi forages on an alani tree in Kaua‘i’s upper forest. Studies by Atkinson and Lapoint show 99 percent of i‘iwi die after a single bite from a mosquito infected with avian malaria. Photo courtesy of Lucas Behnke

Over the last few months, there’s been a lot of scary news about mosquitos spreading human diseases such as dengue fever, not to mention the looming threat of zika.

Have you also heard that mosquito-borne diseases like avian malaria are killing Kaua‘i’s forest birds, with multiple extinctions predicted as a result? Climate change is the probable driver, according to a recent study by Kaua‘i scientists published in the journal Science Advances.

“Collapsing avian community on a Hawaiian island,” published in September 2016 by Paxton et al documents the rapid collapse of Hawaiian honeycreeper populations on Kaua‘i and makes strong links between rising temperatures, rainfall changes, mosquito prevalence and disease.

I spoke with Dr. Lisa “Cali” Crampton, Project Leader for the Kaua‘i Forest Bird Recovery Project, and one of the principal authors of the study about its implications.

Forest birds keep our forest ecosystems healthy by keeping the insects that prey on plants in check, and in turn making sure these plants continue to capture and store water. Also, they pollinate and fertilize plants and trees, ensuring their long-term survival.

An ‘akeke‘e perches on an ‘Ohi‘a tree in Kaua‘i’s upper forest. ‘Akeke‘e have experienced a 98 percent decline in population in the interior of its range during 2000-2012. Photo courtesy of Robby Kohley

Threats to bird populations from rat and cat predation, invasive weeds, and competition from non-native forest birds have been known for quite some time. But this new study shows that a “tipping point” has been crossed where temperatures in high elevation forests have increased so much that mosquitos carrying avian malaria are infecting more and more birds.

Mosquitos need standing water to breed, and the higher the temperature, the faster they develop and reproduce. Also, with fewer hard rain-events to scour the mosquitos out of the streams, they have multiplied.

Six of the seven native Hawaiian honeycreeper species are rapidly declining. The ‘akikiki and ‘akeke‘e, both endangered, declined precipitously in the last decade, with only 468 and 945 individuals estimated to be remaining in the wild respectively, according to the study.

At the same time, a “range contraction” was observed for all of the native birds. Since 2000, four species (‘akikiki, ‘akeke‘e, ‘anianiau, and i‘iwi) experienced the most rapid range contraction and are now only found in a small area of the Alaka‘i Plateau.

Population estimates and distributions for the akeke‘e. On the left panel, linear and exponential population change models fitted to the 2000 to 2012 data are projected from 2013 to 2050 or estimated year of extinction. Areas of distributional range are shown on right panel from 1968 to 2012. Red is 2012, green is 2005-2008, and purple is 1968-1973. Graphic image courtesy of Paxton et al 2016

Two main diseases are decimating these birds. Avian pox causes lesions on feathered surfaces and beaks, which impedes the bird’s ability to perch on a branch or to eat. Avian malaria, an even worse threat, is caused by a blood parasite called plasmodium. Blood samples are showing a higher percentage of birds exposed to avian malaria than previously observed, and Honeycreepers are highly susceptible.

All this points to a real need to control mosquitos, which are non-native to Hawai‘i.

The Kaua‘i Forest Bird Recovery Project is embarking on a pilot project with the United States Geologic Service to examine mosquito biocontrol methods in Koke‘e streams. This method utilizes “mosquito dunk,” a bacillus bacteria that is highly specific to mosquitos and midges, and does not affect other insects, humans or mammals. While Crampton is excited to get started, she said it is only a short-term solution that is very labor intensive.

“At the end of the day we know how grave the threat is and we as conservation biologists would be remiss to not consider all the options, otherwise birds will be going extinct on our watch,” Crampton said.

Global research in the area of mosquito control is ongoing and cutting edge, including the use of male sterilization techniques that could significantly suppress or eliminate the insects from certain areas (in Hawai‘i the mosquito is non-native and was only recently introduced in 1821). Some of these techniques involve bio control, some genetic engineering. In any case, deployment of such methods will only occur after substantial public conversation and thorough research.

In the meantime, here are a few things we can do to help. Keep cats indoors. Reduce artificial mosquito breeding habitat by covering empty buckets or putting “dunk” in standing waters. Donate to or volunteer with KFBRP and other forest conservation groups. Lastly, stay informed about the issues affecting forest birds. Visit http://kauaiforestbirds.org/ to learn more.

• Ruby Pap is a Coastal Land Use Extension Agent at University of Hawai‘i Sea Grant College Program. She can be reached at rpap@hawaii.edu.