Refuge in the Clouds

To get to Hakalau you have to drive through the clouds. Literally. From sea level at Hilo, it’s a two hour drive consisting of a steady ascent along one murderously bumpy dirt road. For everyone who associates Hawaii with warm beaches and white sand, waking up with frost on your windshield and a thin layer of ice on your porch at the foot of the snow-covered volcano Mauna Kea, might come as something of a surprise. But it’s nothing compared to the strangeness of seeing a verdant, tropical rainforest spread out at the foot of a 13,800 ft. volcano. The crazy mish-mash of habitat that has to be seen to be believed. 

At one time in the not too distant past, this land was entirely forested and the great sweep of native rainforest was filled with endemic plants: the Pukiawe, ‘Ohia, Koa, and Hapu’u. Now it is fragmented, chopped into tracts of varying size and smothered by gorse which has arrived in such overwhelming density that it is impossible to escape. Sights like a lone Koa tree rising above the sea of gorse serve as reminders of a forest no longer there.

 But the patches of trees that do remain, persevering in the face of extreme environmental change and adversity, are some of the richest on the entire island chain and are home to many species of native and endangered birds. From the scarlet I’iwi, to the incredible Akiapola'au with its highly specialized beak, numerous endemic Hawaiian honeycreepers have found refuge in the high elevation forests of Hakalau. Curiously enough, while the daily cold mist and rain and the nightly frost and freezing temperatures might be a tourist’s worst nightmare, elevation is actually a honeycreeper’s best friend. Ensconced safely at 6,000 feet above sea level, these surviving species have reached the end of a remarkable elevational migration which took them from the warm lowland forests to trees at the base of the highest volcano in the state.

            The story of the downfall of the Hawaiian honeycreepers and the dramatic range shift of the few surviving species begins all the way back in the 19^th century. At this time, Europeans were arriving en masse to the islands and bringing with them a veritable animal army. Domesticated and livestock animals like cows, pigs, sheep, and dogs were brought across the ocean intentionally, in order to enrich the lives and diets of European settlers. And with these animals, came unintentional immigrants as well: rats and mice and much smaller creatures, the diseases and bacterium that followed their hosts over the waves.

            From the Galapagos Islands to the Hawaiian chain, the story of endemic island wildlife world-wide is largely the same. Evolved from founding species that showed up, storm-blow, wave-washed, and confused, island species developed in relative isolation from the rest of the world for thousands of years. If something didn’t exist on their island, they had no experience interacting with it. This ultimately meant that they fell easy prey to introduced predators like cats, and humans, and the weasel-like mongoose. For an example, consider the Great Auk, a now extinct Icelandic bird which remained fearless of humans even as thousands were slaughtered for food in plain view of the rest of the flock. This evolutionary naivety also includes lacking defenses against common diseases that mainland species have been combating and resisting for thousands of years. Hawaiian honeycreepers are no exception to this general trend. When Europeans brought fowl species infected with a disease causing organism called Plasmodium reticulum to the islands in the 19^th century, it sealed the fate of many Hawaiian birds.

            P. reticulum is a nasty little protist. If present enough in high concentrations in the blood, it causes avian malaria, a disease characterized by anemia, weakness, and pox legions. Initially however, the disease was restricted to the pheasants and chickens the Europeans brought as food and there it would have remained if not for the introduction of the mosquito in 1886. By biting an infected fowl, female mosquitoes themselves became infected with the protist. If they then bit a honeycreeper, the protist would be transferred to this new host via the bite. And, much like the Great Auks who couldn’t defend themselves from their human predators, the Hawaiian honeycreepers had no defense against this new and terrible disease. They too, were slaughtered in their thousands. Over a third of all honeycreeper species on the islands went extinct.

            The survivors are those that have adapted behaviorally to the presence of the protist and its vector species the mosquito. Abandoning the remaining lowland forests, species like the endangered ‘Akepa, the “I’iwi, and the ‘Amakihi, were chased up an elevational gradient until they finally reached forests that were too cold for the mosquitoes to successfully inhabit. Up here, above the clouds in Hakalau, they have finally found some breathing room.

Or so we believe. The truth is, not much is known about how native honeycreepers use this high-elevation habitat. Their home ranges, how far they travel, where they forage and nest, are largely unknown. It might seem a little odd: after all, these are brightly colored birds and their songs fill the forest canopy with continual noise. But they are small, spend most of their time high in the treetops, and are incredibly active making them difficult to track. This means that it’s often difficult to gauge not what parts of the surviving forest are of most use to these birds, and also how much time they spend in newly re-forested sections of the reserve.

            Re-foresting Hakalau has been a long-term project but a necessary one. Although there are no mosquitoes at 6,000 feet above sea level, Hakalau and other high elevation rainforests are still under attack from other unwanted invaders. The gorse, which blooms in such huge numbers that it blankets the landscape in yellow, and the wild boar which forage indiscriminately, uprooting delicate native ferns and vegetation, are two of the most prevalent and damaging species on the reserve. Between them, the rainforest continually loses ground and, if left unchecked, they could quickly overrun what remains. Fortunately, a dedicated corps of wildlife scientists, park rangers, and managers are working to contain both these threats and are re-planting native koa trees where they can. But trees take a long while to grow and the even the oldest groves of new koa are just starting to reach a height that looks forest-like, their understory just now beginning to thicken out with native shrubs and bushes.  

While this new forest looks promising from a human-perspective (Trees? Check.  Vegetation? Check) evaluating how effective this reforestation really is, understanding if these new tracts of koa are forming usable habitat for native species, requires one to follow the birds. In addition to setting up net lines to catch, band, and count individual honeycreepers, scientists at Hakalau have experimented with the delicate art of attaching tiny radio transmitter backpacks to individuals. Worn like a mini-harness, these miniscule transmitters bleep out the location of their owners as the birds travel through the landscape. The signal is picked up by special receivers, with each individual bird on its own frequency, and with enough dedication and ample luck, one is able to track the honeycreepers as they navigate through the reserve. By calculating where they spend the majority of their time and how often they choose to inhabit the tracts of new koa, scientists are hoping to better quantify the success of the reforestation effort.

In 2011, I spent a month in Hakalau working for the USGS, catching and tracking honeycreepers through the rainforest. There is nothing like holding the receiver and antennae in one hand, and trying not to slip and slide down stream banks, into giant tree ferns, or off elevated forest ridges to give one a healthy respect for just how far and effortlessly these birds travel over such thick terrain. Occasionally, I would look up and see them, darting high above me in flashes of wings and bright color.  Their songs made the beep of my radio seem tinny and subdued. Every so often they would alight when they thought you weren’t looking, and would sit on the wet branch of a Koa or ‘Ohia tree, fluffing up their vivid plumage and blinking their eyes against the light rain that came streaming down through the canopy. Inadvertently we have chased these remarkable birds here, to their last cloud-shrouded bastion, and we are now following them through it, chasing their vibrant afterimages through the dense trees, waiting and watching to see where they will go next.