The Kingdom of Rarities (30 page)

Many scientists have warned about the spread of tropical diseases with shifts in climate, but few have considered its impact on particular species of wildlife, especially rarities. This is an issue that extends far beyond Hawaii. Species are beginning to head uphill to find cooler and often wetter refuges, and as the climate warms further, their chances of success are likely to decline. Shifting one's range up a mountain is especially problematic for organisms other than birds because of limited mobility options.

We returned to Hilo in time for the opening plenary lecture by David Steadman, an authority on extinctions in the Pacific region. Part-time comedian and full-time paleontologist, anthropologist, and evolutionary biologist, he related an ecological history that captivated many in the audience who were new to the region. Steadman projected a map of the Pacific Ocean on the screen. Pointing out the island groups in the order that they were discovered by Polynesian sailors, he showed that the Hawaiian Islands were among the last. Anthropologists generally date the first landing on Hawaii by the Polynesians (who hailed from the Marquesas Islands) around AD 1200–1300, although some experts set their arrival more than 800 years earlier. The prevailing winds, which skirt the Hawaiian archipelago, had discouraged human settlement longer than had
been the case anywhere else except New Zealand and Easter Island. After the initial discoveries, several more migrations to the Hawaiian Islands occurred from Tahiti and elsewhere. Along with them came the normal passengers for colonization and exploration—taro root, bananas, coconut palms, dogs, hogs, and chickens—and the stowaways, the Polynesian rats.

When Captain James Cook arrived in 1778, the total human population was less than 1 million. But by then the biological effects of the Polynesian invasion were well established in Hawaii, just as they were wherever else the Polynesians had landed across the Pacific.

Polynesian farming practices involved widespread clearing and burning of the lowlands, a process that wiped out those species adapted to life along the coast. New information suggests, however, that the Polynesian rat may have played a bigger role in the demise of the native birds than did land clearing. The naïveté of native birds that had evolved in the absence of predators such as rats had left them defenseless. The birds weren't able to migrate or to evolve quickly enough ways to protect their nests. So the rats ate the eggs and nestlings, reproduction plummeted, and many species passed into oblivion.

Steadman's current focus is across the South Pacific, where he spends his days in bird graveyards reassembling the rich faunas that were clubbed to death by hungry Polynesians and exploring lavaisolated pockets where the fossils are the result of natural mortality. His observations illustrated the importance of an ecohistorical approach to understanding contemporary rarity and extinction. For example, his research sheds light on the extent and timing of the start of the biodiversity crisis on Pacific islands by showing us that a steep decline in species occurred nearly 1,000 years ago. It also offers clear evidence that natural rarity was exacerbated by invasion of humans and the fauna they brought with them.

After Steadman's talk, I asked Thane Pratt about the list of obituaries and the percentage of those species that were flightless. He
listed 5 species of geese (plus 1 not yet described by science), 2 ibises, 1 hawk (possibly 1 undescribed), 1 eagle, 5 rails (plus around 5 undescribed), 4 owls, 2 crows (plus 2 undescribed), 18 honeycreepers, and more recently a flightless duck from Kauai that went extinct, for a total of nearly 40 extinctions. Of these described extinct species, 13 were flightless, to which could be added 6 undescribed flightless species, for a total of 19. Add the historical Hawaiian and Laysan rails and you have 21 species that had lost their ability to fly to safer ground when faced with a new threat and that had perished as a result. That's only a short list of what was lost before the arrival of Europeans, based on the species paleontologists have identified from several excavations scattered among the islands. The true number of extinctions remains a guess.

Sitting in a darkened auditorium listening to one scientific talk after another can induce slumber. So much talk about extinction also rekindled my desire to get out and see these rarities before they disappeared. Later that morning, our bird-seeking group returned to the upland forest along the Saddle Road, where Liba once again was our guide. A tip steered us to the Pu'u ‘Ō'ō Trail for spotting ‘akis. “
Pu'u
” means hill, and “
‘ō'ō
” is the name of an extinct Hawaiian bird that represented an endemic family, closest to the silky flycatchers and waxwings. The ‘ō'ō must have been a dashing bird, a jet-black honeyeater more than thirty centimeters long with yellow epaulets and undertail coverts. So coveted was its plumage that many were slaughtered for the feather trade, reportedly as many as 1,000 individuals around 1898 just outside of Hilo. By 1987 the ‘ō'ō had been wiped out, the victim of habitat loss, hunting, and disease, illustrating once again that there are usually multiple causes, not just one, for such an ultimate fate.

A kilometer along the trail in the upland forest, we passed through groves of koa.
‘Amakihis
and ‘apapanes were about, but no ‘akis. Then suddenly Liba signaled that she'd heard the song
of the ‘aki. We bushwhacked for several hundred meters to where the ‘akis were calling, and there the birds sat, perched in a koa. An ‘akiapōlā'au could appear as easily in an illustrated book of fairy tales as in a field guide. The color of the male's plumage adds a brilliant new interpretation to the color yellow. The ‘aki uses its straight lower bill to hammer at tree bark like a woodpecker. Then it uses its long, thin decurved upper bill like a one-armed tweezer to pull out tasty grubs. David Wilcove describes the ‘aki as a bird with “a Swiss army knife for a bill.”

“That's not the only foraging trick up their sleeves,” Liba explained. “They can also thrust out their lower bill so that the tips meet and use their mandibles like pliers.” She went on to tell us about the most interesting discovery of all: these pseudowoodpeckers also behave as sapsuckers do on the mainland. A major part of Liba's field research was devoted to trying to understand why ‘akis use “aki trees,” or sap trees. Typically the birds forage on koa trees, but about 5 percent of the time they forage on ‘ōhi'as, yet not for insects and grubs—they're after the sap, much like North American sapsuckers. “They drill into the surface of the bark and into the vessels in which the sap streams (the phloem). Then, while holding their slender upper mandible out of the way and using their lower mandible as a guide, they drink the sap with their tongue. You see them touch the tip of their bill or their tongue to the sap over and over.”

Liba's eyes widened as she recounted her discovery of the secret life of her study bird: “If you stick an ‘aki tree with a nail, as I did many times, the sap comes flowing out, and it is quite sweet.” But the amazing thing was that she found the opposite to be true for the ‘ōhi'a trees she tested that showed no evidence of previous hole drilling. When she poked those with a nail, no sap emerged.

“Somehow the birds know which trees are productive. Or perhaps they make them productive by changing the flow and pressure of the sap,” Liba commented. Many of the ‘aki trees that produce sap are covered in holes from roots to canopy. By following the
birds she had located, she found that each pair had as many as seven to ten sap trees in their particular home range. It turns out that only about one in a thousand ‘ōhi'a trees is a sap-giving tree.

‘Akiapōlā'au (
Hemignathus munroi
) looking for grubs

When it comes to rarities and even common species whose numbers are falling, the problem we face now is how fast the current activities of
Homo sapiens
are speeding up extinctions of everything Hawaiian, from land birds to snails to plants. The loss of birds, though, is the most obvious. “What really surprised me about the Hawaiian birds,” Liba said, “was their susceptibility to the devastating impacts of invasive species by predation, competition, and disease.” She sounded as if she were preparing an epitaph. “Few
species have survived the plague that is avian malaria, the loss of key host plants such as lobeliads to pigs and other ungulates, and nest predation by rats and cats. I'm not sure there is anywhere else in the world where invasive species have had such a dramatic effect on a native avifauna.”

Yet surprising data from another part of her ‘aki study offered a glimmer of hope: “Remember the beautiful old-growth koa forest we walked through in Hakalau Forest? The one you thought looked like Middle Earth from
The Lord of the Rings
? When I started my ‘aki project, most folks assumed ‘akis were rare in part because they depended on big, old koas in places like Hakalau Forest.” Most biologists were simply buying into the conventional wisdom of rarity theory: rare habitats should be where rarities are concentrated, and because there was little old growth left, the ‘akis that depended on them were on their way out. Only it turned out that the ‘akis didn't depend on the koa old growth exclusively.

Liba discovered that ‘akis actually lived in higher densities in ten-year-old koa stands than they did in the old-growth koa forest of Hakalau Forest National Wildlife Refuge. She mapped home ranges at Hakalau Forest and on her study site covered by young koa trees at Keauhou Ranch, on the western side of the Big Island. “In the Hakalau refuge, ‘akis have home ranges that roughly fit together like pieces in a jigsaw puzzle,” she said, referring to the territories ‘aki pairs had carved out for themselves. But she found the opposite to be true in the young stands at Keauhou: there, ‘akis seemed not to be as territorial. Their home ranges overlapped almost entirely, with males defending females rather than chunks of forest. There are two parts to the explanation for this: first, she documented that ‘akis spend about 90 percent of their time foraging on koa; second, she suggested that young, thick stands of koa offer a much higher density of food than do scattered giant koas in mature forests dominated by ‘ōhi'a trees, such as Hakalau Forest's old growth. “In short,” she concluded, “more food, more ‘akis.” Biologists working on other species, such as carnivores, show that territoriality becomes
relaxed when the food supply is so abundant there is no need to defend parcels of land as hunting grounds. Such behavior would represent wasted energy, and there would be selection against it.