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July 20, 2000

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Forest birds of the Hawaiian Islands

Several million years ago, when Kaua`i was the youngest island in the Hawaiian archipelago, and Pele made her home in the caldera atop Mount Waialeale, a small flock of finches made landfall somewhere in the Hawaiian Islands, exhausted from their trans-Pacific journey. Perhaps they had been blown off-course by a hurricane.

The odds against their making the crossing, 2,500 miles over open ocean, were staggering. If the birds were able to find food to eat, cover from the elements, mates, and suitable places to build their nests, they would have thrived. For here there were no mammals to prey upon them, no diseases to sicken them, and few, if any, other birds to compete with them for food or nest sites.

In this profound isolation, with a variety of food sources and habitats, some of the colonists did, in fact, thrive. Very slowly, over millions of years of evolutionary time, the original finch species evolved to become several separate species, each adapted to exploit a different foraging style or habitat. This process, called adaptive radiation, eventually gave rise to a spectacular array of forest birds found nowhere else in the world.

The flame-red 'I'iwi, for example, evolved a long, sickle-shaped beak specially adapted for sipping nectar from the long tubes of lobelia flowers and ohi`a-lehua. The 'Akiapola'au, with its elaborate two-part beak, is particularly skillful at extracting insect larvae from dead trees. The Palila has developed a thick, strong beak for crushing the hard seed pods of mamane trees. These diverse birds, along with 29 others, make up the group we know as the Drepanidinae, or Hawaiian honeycreepers. From North America, Asia, and the South Pacific, other kinds of birds came, carried on the winds of other storms. At the same time, as the older islands submerged into the sea and new islands were formed, the birds dispersed and evolved into yet additional isolated and specialized forms. By the time Polynesians arrived, in addition to the honeycreepers, the archipelago harbored its own species or subspecies of crow, hawk, rail, owl, duck, goose, coot, and stilt, as well as two petrels, five thrushes, five honeyeaters, and five types of `Elepaio.

Forest birds became integral parts of Hawaiian ecosystems, serving as pollinators, seed dispersers, and insect predators. They also became integral parts of Hawaiian culture, the brilliant yellow feathers of the `O`o cloaking the king, and 'Elepaio guiding canoe makers to the best koa trees.

Tragically, the very isolation that encouraged this amazing radiation has also been the birds' undoing. Sheltered on the islands for millions of years, the birds lost their ability to deal with mammalian predators and disease. Introduced cats, rats, and mongoose found Hawaiian birds easy prey. Avian malaria and pox devastated bird populations, much as other new diseases devastated the native Hawaiian population after Western contact. Alien plants and feral ungulates (hoofed mammals) degraded the birds' habitat, and exotic birds and introduced insects competed with native species for food.

As a result, about half of the original Hawaiian birds have become extinct since human contact, and about half of the remainder (31 species) are endangered. Many species - the Nukupu'u, for example, and the Bishop's `O`o - slipped into oblivion before we could even record what they ate or how they raised their young.

Public concern for the natural heritage of Hawai`i has inspired growing efforts to study the remaining birds and to develop safe, cost-effective methods for protecting and recovering them. The goal is to preserve the honeycreepers for our children's children, so that long after the newest volcano in the Hawaiian chain, Lo`ihi, has broken the surface of the ocean, and her slopes have become cloaked in rainforest, a small honeycreeper may find its way there in a storm and begin the process of adaptation and speciation anew.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the past week. Lava is erupting from Pu`u `O`o and flowing through a network of tubes toward the coast near the eastern boundary of Hawai`i Volcanoes National Park. Multiple areas of the flow field in the coastal flats are inflating and forming tumuli and pillow-like lobes. Lava is entering the ocean mainly at two locations: Waha`ula and Kamokuna. Several small entries, located to the east of Waha`ula, are weak and ephemeral. The public is reminded that the ocean-entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The active lava flows are hot and have places with very thin crust. The steam clouds are highly acidic and laced with glass particles.

A resident of Leilani Estates subdivision felt an earthquake at 4:29 a.m. on July 16. The magnitude-2.4 earthquake was located 5 km (3 mi) east of Pu`ulena crater at a depth of 4.5km (2.7 mi).

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Updated: 24 July 2000