The locked gate on the private, unpaved road in lower Puna is unremarkable. Like hundreds of others that lead to the area’s papaya orchards and scattered houselots, it effectively bars access to all but those privileged with padlock keys or codes.
The 200 acres that lie beyond the gate, however, are as unlike the houselots and orchards as night is from day. A high canopy of ‘ohi’a and the rare ‘ohe’ohe casts the thick understory of tree ferns into a permanent twilight. The existence of a near-pristine native lowland forest in the midst of degraded lands, exceptional though that is, is not the greatest secret locked behind the gate. That distinction falls to the thriving population of ‘amakihi inhabiting this small patch.
The survival of native birds in lowland areas defies the expectations of many bird experts in Hawai’i. With avian diseases (pox and malaria) rampant at elevations where their vector (mosquitoes) is found, and with native birds exhibiting little natural resistance to those plagues, received wisdom held that lowland areas, even when relatively undisturbed, could not support the natives.
How, then, can these Puna ‘amakihi be explained?
Pat Hart, a postdoctoral fellow at the Kilauea Field Station of the U.S. Geological Survey’s Biological Research Division, is one of 13 scientists from six institutions hoping to find the answer. Under a canvas canopy, he and 10 interns mull around their field research station – two tables overrun with equipment, from high-tech computers and spectrometers to needles and pencils. In the forest, fine mist nets have been strung between trees. Every half-hour, so long as the nets are up, the researchers patrol them and deftly remove any birds snared in the invisible lines.
On one early morning net round, Bridget Frederick, an intern, gently plucks off two docile Japanese white-eyes (Zosterops japonica) and an aggressive cardinal (Cardinalis cardinalis), non-native birds that have become established throughout Hawai’i. In most forests, only 10 percent of the birds are native to Hawai’i, while about 90 percent of the birds are native at elevations around 1700 meters above sea level. However, in some lower Puna sites, up to 60 percent of the captured birds are ‘amakihi (Hemignathus virens), a member of the Hawaiian honeycreeper family.
By ten o’clock, the group has caught two ‘amakihi, a juvenile and an adult male. The chick is little more than a puff of gray down and could rest comfortably in a soup spoon; an empty M&M pack could be the sleeping bag for the adult, a dull, green-yellow bird except for its bright yellow head.
At the fourth net, Frederick and I hear the ominous sound of an oncoming rainstorm, like an approaching transport truck. We get drenched. The path instantly turns to mud, and two nets remain to be examined. While Frederick runs to check the nets, a voice over the two-way radio blares, Everybody in, everybody in. For the next two hours, the researchers wait, hoping to outlast the rain. The rain wins. By noon, the group calls it quits, ending the day’s search for ‘amakihi at this site.
Finding ‘amakihi in the lowland forests gives conservationists hope that ecosystems once thought to be inhospitable to native birds may actually be home to unknown numbers of them. What’s more, it challenges the popular notion that native birds cannot survive in areas rife with mosquito-borne disease.
Changing Models
The introduction of mosquitoes occurred accidentally in the 1820s with the arrival of a whaling ship bearing mosquito larvae in its casked water. Half a century later, bird aficionados began importing birds into Hawai’i. With the islands already infested with mosquitoes, it took only a few diseased animals to be included for conditions to be ripe for an epidemic among native Hawaiian birds.
This was first noted in the early 1900s, when naturalists began to observe a decline in native birds, even though their habitat seemed relatively undisturbed. Not until the 1960s, though, was the link among disease, birds, habitat, and mosquitoes described scientifically by Rick Warner, a former avian ecologist at the University of California at Berkeley. Warner was the first to formulate the idea that habitat changes include not only visible alterations to the landscape, but the onset of disease and disease vectors as well.
In the 1980s, Charles van Riper, an avian ecologist now at Northern Arizona University, observed that native birds are rarely found in the lowlands and instead tend to inhabit the mosquito-free, colder zones at high elevations. He speculated that the native birds disappeared from the lowland portions of their natural ranges after the arrival of disease-carrying mosquitoes.
The van Riper model became widely accepted among ecologists and conservationists. “It was very influential,” says Hart, “and is widely cited in ecology textbooks…. It’s almost become dogma.”
However, a few years ago, researchers at the University of Hawai’i-Manoa and USGS began to see native birds where the model said they had no business being. This led eventually to the Biocomplexity of Avian Disease Project, the work of a collective of demographers, ecologists, parasitologists, geneticists, and modelers that aims to understand better the intricate workings of Hawaiian biological systems.
“We’ve been trying to figure out the reasons for why these birds could be existing down here if there is so much disease,” Hart says. “A lot of people are saying, ‘Yeah, they are down there but they’re just transients.’ By banding the birds monthly, we found that the birds are present year ’round at low elevation. Not only do they come into breeding condition like a normal population of birds would do, but they are in breeding condition for longer periods of time than birds that are in mid to high elevations.”
Adapting
In the time the field researchers have with the birds, they weigh and catalogue them and collect blood samples. Just a few drops are enough to tell which ones have or have had malaria.
Carter Atkinson, a microbiologist with USGS-BRD and co-investigator on the project, says, “Numbers of ‘amakihi with malaria at low elevation sites are extraordinarily high. More than 90 percent carry active infections yet do not seem to exhibit any clinical signs of the disease… That is really surprising because based on experimental studies, more than 60 percent of most honeycreepers that become infected die from the disease.”
Simply put, ‘amakihi are either becoming resistant to malaria or the disease itself is changing and becoming less virulent. Susan Jarvi, a geneticist at the Kilauea Field Station, is comparing the genetic profiles of low-elevation ‘amakihi that have been exposed to disease to that of high-elevation ‘amakihi most likely not exposed. Preliminary results show that there are indeed genetic differences between the lowland ‘amakihi and their highland relatives, suggesting that certain genes in the lowland birds may be associated with malarial resistance.
Jarvi’s work may someday assist efforts to conserve ‘amakihi and other native birds affected by disease. By knowing what genetic profiles are linked to malarial resistance, it might be possible to “genetically distinguish resistant birds without having to infect them,” she says. This would be “critical for captive breeding and release programs, as well as assisting in maintaining a high level of overall diversity in populations,” she adds.
The ‘amakihi of lower Puna may also give scientists a glimpse into adaptive radiation, an evolutionary process that results in new traits and, over the long haul, even new species. The Hawaiian honeycreepers are one of the world’s most extreme examples of adaptive radiation. It is thought that one species of honeycreeper came to the islands approximately four million years ago, became isolated from its genetic relatives, and subsequently transformed into at least 54 different species.
“The process of evolution is continuous,” Jarvi said in an email interview. “To be able to document ‘snapshots’ of this process is very exciting.”
A Bird In Hand
At a second collection site, also in lower Puna, ohi’a trees still dominate, but they preside here over sun-exposed patches of ‘a’a lava and invasive grasses.
Leigh Stuemke, an intern, takes me out on net runs. She makes the delicate unknitting of a bird caught in a mist net look easy.
Back at base camp, a steady influx of tiny, quivering birds queues up for examination. As the birds’ blood is drawn, the interns call out numbers and terms that are bewildering to an outsider. From this confusion, the researchers are beginning to know what birds are surviving in this seemingly inhospitable habitat, and how.
An intern holds up a bird. He looks at it intently, gives it an affectionate peck in the air, and lets it go.
— Trevor Stokes
Volume 14, Number 2 August 2003