The Kingdom of Rarities (29 page)

Fortunately, on our way back to Hilo we took a wrong turn. Quite by accident, we found ourselves facing a feeding party of palilas and an
‘elepaio
, the endemic Hawaiian descendant of an Australasian flycatcher. As we enjoyed the spectacle we had hoped to see, we also scanned the panorama of hills and fragmented forest perched above the converted, sugarcane- and pineapple-planted lowlands. The palila's strategy for survival became obvious, mirroring what all resistance fighters know instinctively: when the invader advances, head for the high ground—in this case, where the māmane forest was still present.

To improve our chances of seeing native Hawaiian fauna and flora, we continued a search of Hawaii's uplands, choosing Hakalau Forest National Wildlife Refuge. Our group was fortunate to have as a guide Jack Jeffrey of the US Fish and Wildlife Service, who has been the force behind conservation at Hakalau for several decades. A young scientist studying the birds of Hakalau Forest, Liba Pejchar, now an assistant professor at Colorado State University, also served as a guide. Liba's specialty was none other than the
‘akiapōlā'au—
‘aki
for short—the renegade honeycreeper that had evolved to become the island's de facto woodpecker. For several weeks, she had been watching a male make feeding trips to a female and their young. Although it feeds like woodpeckers and sapsuckers, the ‘aki does not nest in tree cavities; instead, it makes a cup nest in the terminal branches of the ‘ōhi'a tree. If we were lucky, our group would see this rare honeycreeper, but to find even one of the remaining 600 pairs spread over several thousand square kilometers in only three hours would indeed require a blessing from the birding gods.

We walked through a stand of tall ‘ōhi'a and giant koa trees—Hawaiian old growth—which gave way to meadows and back again to forest. For a biologist and lover of fantasy fiction, our hobbit-like experience of walking through open glades interspersed with groves of giants with their odd architecture was like a walk through Tolkien's Middle Earth. It's an ancient landscape, too: some of the ‘ōhi'as have been carbon-dated at over 400 years of age, making them possibly the oldest nonconiferous trees in the entire United States.

Jack's knowledge of Hawaiian natural history flowed nonstop. He pointed out that the lack of native mammalian herbivores had allowed native vegetation over evolutionary time to lose defenses against being eaten: spines and thorns and waxy leaf cuticles and other chemicals that make plants taste bad. Thus, the native raspberry in Hawaii has many fewer and softer thorns than do raspberries elsewhere, the native nettle has lost its stinging hairs, and the local mints no longer produce the strong aromatic oils that emit their characteristic fragrance in other lands. David crushed the leaves of a nearby ‘ōhi'a, expecting the small, fuzzy foliage to release a strong guava-like aroma. This dominant Hawaiian tree is a member of the eucalyptus family, known for the powerfully volatile oils infusing the trees' leaves and bark. He inhaled deeply, but there was no smell. Like other native Hawaiian plants, the ‘ōhi'a no longer needed to repel large browsing mammals as had its evolutionary
ancestors, and so, over time, its costly perfume factory had shut down.

Koa (
Acacia koa
), the other old-growth tree species here, is one of a strange-looking group of acacias. Most wildlife tourists associate “acacia” with the umbrella thorn acacia,
Acacia tortilis
, the flat-topped tree of postcard East Africa. Most amateur botanists recognize the genus
Acacia
by its bipinnate compound leaves and wicked thorns. These features aren't present in the koa, though. That's because there aren't any leaves, at least not on adult koas. Instead, koas photosynthesize with structures botanists call phyllodes—flattened petioles, or leaf stems, that serve the purpose of leaves and resemble small green boomerangs.
Acacia
species with phyllodes instead of leaves are a phenomenon seen only in Australia and the Pacific islands. Nearly all Australian acacias lack thorns and photosynthesize with phyllodes. And with no giraffes or elephants in the Hawaiian fauna, koa trees, of course, didn't need thorns either.

We started to see clusters of ‘i'iwis and a number of ‘apapanes, the other red nectar-feeding honeycreeper. Along the way, Jack pointed out a tall, familiar-looking plant with large greenish-purple curved flowers. It was a lobelia—related to the cardinal flowers American birders grow to attract hummingbirds. This was no common cardinal flower, though, but one of the rarest plants on Earth.
Clermontia pyrularia
had nearly gone extinct, but Jack and his colleagues had managed to rescue it. Now this species and other lobeliads are propagated and transplanted back into the wild. Jack and his colleagues are focusing the same kind of intensive restoration efforts on some rare mints that Jack discovered. Some of the other honeycreeper-pollinated plants, like the lobelias, are now imperiled because they have lost their pollinators and must be handpollinated in the field to keep the populations alive.

When I asked Jack about restoration of Hawaiian silverswords, his eyes lit up. Silverswords, which take their name from the long, narrow leaves and silvery hairs found on most species, are a
Hawaiian rarity that some plant conservationists have devoted their lives to saving. These plants can live to be fifty years of age, show remarkable adaptations to cope with rarity, and have an odd life cycle, waiting until the end of their life to send up a flowering stalk and then fruit before dying. Silverswords, which also go by the far less poetic name of tarweeds, belong to the genus
Argyroxiphium
, a small group of five species in the sunflower family. But like the honeycreepers, silverswords radiated into an array of more than thirty species. This group is known as the silversword alliance, a brother- or sisterhood of plants adapted to living under extremely harsh conditions—under the volcano and on its cinder fields or in acid swamps known as bogs. How could plants that survive the tough life in the shadows of volcanoes, exposed to wind and freezing temperatures and desiccation from intense sunshine, and those that thrive in bogs and in such low-nutrient soils, have become so rare? Volcanoes and bogs should be the boot camps for rare plants, toughening them up and allowing them to resist any disaster, manmade or natural. Silverswords even show peculiar adaptations enabling them to raise their body temperature by focusing sunlight on the shoot tips. What they are not adapted to is the trampling of pigs and browsing of goats that have been introduced here. Their thinly buried roots, especially those of the bog-loving species, are easily destroyed, and their succulent leaves are prime delicacies for goats.

Even before humans arrived on the islands, all species of silverswords had very limited ranges, and they remain vulnerable to extinction. Some populations are quite numerous, such as the Haleakala silversword, found only in an old crater on Maui. Its entire global distribution is limited to this one site, but this tiny area supports more than 40,000 individuals. Yet however common this species of silversword may be locally, all its eggs, or seeds, are in this one basket. Lose this site to pigs and goats and you lose the species forever. Jack and his colleagues, in addition to being botanists, have become world-class fence builders and goat rustlers, courses never taught in the ivory tower but essential to study and save rarities in the wild.

Scanning the trees, Jack and Liba spotted a honeycreeper we hadn't yet seen that day. The
‘ākepa
dazzles beholders with its burnt-orange plumage and slightly crossed bill, which enables it to pry open leaf buds for prey. Suddenly the sounds of the native birds were drowned out by the exotic red-billed leiothrix and a flock of Japanese white-eyes. One person asked, “If you erected a mist net to capture birds, would you catch more native or exotic species?” The ratio, Jack replied, would be about ten individuals of native bird species for every introduced one. We were relieved to hear that, in an archipelago full of things from everywhere else, native Hawaiians still reign in Hakalau Forest.

When our party stopped for lunch, a native fruit fly landed on a bush near David, perhaps attracted by his fruit salad. In Hawaii, fruit flies form new species like an out-of-control experiment. Since any individual fly could be new to science, it was tempting to thrust it into alcohol and send it on to a fly taxonomist. Identified so far are five hundred species of fruit flies that swarm wildflowers all over Hawaii, but some experts estimate that the number of known species will increase. Fruit flies are not particularly endangered, as are many honeycreepers, but like them some are quite beautiful and ornate, far more compelling than the red-eyed, vestigial-winged mutants of genetics class. Other insects were about, but if we looked closer, we would find only introduced ant species grubbing for our lunch spoils. Ants never made it to Hawaii before human introduction, and many of the arthropods that did arrive, like many birds, shed their wings to become flightless versions of their mainland ancestors. Hawaii has a depauperate collection of insects in terms of number, but those that do occur on the islands are highly endemic and often have narrow ranges. Remarkably, the Hawaiian Islands have more species of fruit flies than are found in the rest of the world combined. “First in Fruit Flies”—not a slogan that will appear anytime soon on automobile license plates in Hawaii, but of profound interest to biologists.

First honeycreepers, then silverswords, and now fruit flies are showing us how rare species persist in a compressed space and how
adaptive radiation results in many new species that themselves are rare. Adaptive radiations have occurred in many places—in South America and Australia and even in Mexico's Chihuahuan Desert, home to a great radiation of prickly pear cacti, evening primroses, and desert fish (cichlids), wherever the necessary conditions have prevailed. But it is easier to study radiations on island archipelagoes. The Galápagos Islands are home to radiations of finches, mockingbirds, tortoises, and giant dandelions.

The fruit fly kept hovering about; evolutionary marvel or not, I would have traded encountering ten new species of fruit fly for a single ‘akiapōlā'au. We resumed our walk, hoping to catch sight of the faux woodpecker. Liba showed us the nest, to which the male typically returned about every forty-five minutes to feed the female. Our plan was to sit silently under the tree and wait. A half hour into the vigil, Liba stood up and pointed to her left. She had heard an ‘aki calling in the distance. We heard nothing except red-billed leiothrixes, house finches, and white-eyes, all imported singers.

The hour was late, so we had to end the stakeout. Jack suggested that everyone come back to Hakalau Forest during the breeding season (December through May), when the native birds would be more active and vocal. Then the trees would be “dripping with ‘i'iwis,” and maybe an ‘aki or two. Liba chimed in: “People expect all honeycreepers to be rare everywhere, given all the threats they face. But the dawn chorus at places like Hakalau Forest is unbelievable; it's deafening. I think songbirds are at higher densities here than almost any forest I've visited.” Honeycreepers have declined in the lowlands of all of Hawaii's archipelago partly because the dense forests of native plants have been replaced by a generic pantropical vegetation including eucalypts from Australia, banyan trees from India, and jacarandas from Brazil. On Oahu, if you relied on the most common plants to distinguish where you were in the world, you might think you were in Bermuda, or St. Croix, or even a Club Med in the Seychelles. Most of the trees and shrubs that line the roadside display large, showy flowers in an orgy of colors, imported
beauty that has increased the diversity of plants in Hawaii but fails to attract its native birds.

Introduced species of birds and mammals are also responsible for pushing some of the rare natives out of the lowlands. According to Thane Pratt, the leading authority on Hawaiian birds, more than 170 alien bird species have been introduced onto the Hawaiian Islands, about 54 of which have established breeding populations. Like their floral counterparts, they came from the world over—red-billed leiothrixes, rose-ringed parakeets, and bulbuls from Asia; waxbills and canaries from Africa; cardinals and meadowlarks from the Americas. These and most of the other introduced avifauna are all beautiful birds, but they don't belong in Hawaii.

The most pervasive factor accounting for the absence of native birds below 1,500 meters' elevation is unexpectedly small. The accidental introduction of mosquitoes in the early 1800s allowed avian pox and avian malaria to spread from infected migratory birds or species introduced from Asia to the defenseless native birds, wiping out a number of species and populations in the lowlands. The remaining species were those that ranged into the higher elevations, where it is too cool for the
Culex
mosquitoes to survive.

To imagine the ‘aki and the other honeycreepers joining the dodo, the great auk, and the elephant bird in the aviary of oblivion is a painful thought. Jack is concerned that with rising temperatures resulting from global climate change, the temperature-sensitive malarial parasites could develop fully within their mosquito hosts. Then the disease could make its way up the mountainsides and adapt to life in these forests, wiping out the remaining native birds as it goes. (Studies of human malaria show its projected spread to higher elevations and latitudes for the same reason.) Birds at still higher elevations might be safe for a while, but how much farther uphill can they move before the forest gives way to the cinder fields characteristic of the volcanic peaks?

The observatory by the summit of nearby Mauna Loa gives us some context for contemplating that question. The Mauna Loa
atmospheric carbon dioxide (CO
₂
) measurements, which began in 1958, constitute the longest continuous record of changing atmospheric CO
₂
concentrations. Earth's atmosphere mixes globally so that the CO
₂
component at Mauna Loa, where there are few local inputs to the atmosphere, is a good gauge of the overall fraction. The methods and equipment used to obtain these measurements have remained essentially unchanged during the five-decade monitoring program. The Mauna Loa record shows a major increase in the mean annual concentration of CO
₂
, from 316 parts per million by volume (ppmv) of dry air in 1959 to 385 ppmv in 2010. In short, the increasing amounts of CO
₂
in Earth's atmosphere are real and serious.