The Kingdom of Rarities (6 page)

The oblivious male began emitting a rasping growl that sounded a bit like gravel being poured out of a dump truck. This vocalization helped Bruce and his team find many other bowers. The dancers themselves could be easily spotted circling around their one-meter-tall fabrications. In the tranquility of the Fojas, the bowerbirds proved anything but shy.

A day later, it was the turn of another quest species to make its grand entrance. A pair of Berlepsch's six-wired birds of paradise appeared at camp, cavorting in from the forest edge. Equipped with shiny black-and-white plumage, the male began to shake his feathers, including the six ornate wirelike feathers emanating from his head, the basis for the name of the species. He then began to flick his wings, flash his white flank plumes, and utter sweet call notes while closely circling the female. The display lasted for more than five minutes.

The scientists were awestruck. No one had witnessed the courtship dance of this species before. The six-wired's place of residence was unknown before this expedition; it was a species collected before 1897 from an uncertain locale and not by a naturalist. No one
had even managed a good look at the adult male—Jared Diamond had caught only a glimpse of this “lost” bird, a female, in his earlier expedition. It had been listed as a subspecies of another six-wired for nearly a century, but Bruce instantly recognized it as a potentially distinct species because of its unique vocalizations and slightly varied plumage and eye color. Given so many isolated ranges on this island corrugated with mountain chains, it's no wonder that New Guinea is home to thirty-seven species of birds of paradise. Bruce and his team worked straight through the daily downpours. Over the next two days the marsh in the bog flooded, turning the helicopter landing site into a lake and forcing him to move his tent and much of the campsite to higher ground. On the plus side, the mystery bird with the chicken wattles, the new honeyeater, was everywhere around the newly flooded bog. Oddly, it made no vocalization, an unusual trait for a bird.

There was another striking aspect of the birds up here. Previously, Bruce had logged many hours of observation concealed in blinds on Mount Missim, about 750 kilometers away in PNG, recording the breeding and feeding behavior of four local species, both rare and common, of secretive birds of paradise. But in the upper Fojas, a bird blind was unnecessary. The male Berlepsch's six-wired bird of paradise ignored the visitors and continued to dance vigorously. The golden-fronted bowerbird males could be observed constructing their bowers up and down the ridgelines, and by the end of week one, the wattled smoky honeyeater had become a camp bird. Nearby, the black sicklebill continued flirting with the females from atop a dead stub on a forest ridge.

What made the birds so unafraid of predators, nonhuman or human? Bruce's field notes from the expedition indicated relatively few hawks, falcons, and eagles during his bird surveys. Perhaps their densities were too low to provide much of a threat to the displaying birds. Then, too, there were none of the midsized and smaller wild cats that frequently prey upon birds west of Wallace's Line. As for the human influence, one might expect much more secretive behavior
if hunters regularly passed through. Finally, if such breeding displays are genetically hardwired, the birds can't help themselves from becoming momentarily oblivious to everything else. In the desire to breed with a female, what Darwin termed “Nature's urge,” being a shy wallflower conferred no selective advantage. A male had to step out on the dance floor if he wanted to mate and pass on a copy of his genes to future generations.

Birds of paradise have fascinated indigenous peoples and scientists alike, and those on Bruce's team were no exception. The sixteenth-century Spanish explorers who named the species they encountered believed that these birds were emissaries from heaven. Some Europeans in the nineteenth century even assumed that birds of paradise were ethereal, legless creatures that never touched ground. Birds of paradise are native to New Guinea and surrounding islands, with only a few species resident in northern Australia. Many in this family of forty species dazzle biologists with their bright, metallic wirelike feathers, brilliant gorgets (throat patches), and elaborate tails. Their mating dances, full of shakes and shimmies, put those barbs and bristles in best light to advertise their fitness to interested females. Today most species are not threatened and some are widespread, while others fit the definition of rarity by occupying slivers of altitudinal ranges along the flanks of the steep mountains.

Back at camp, Bruce thumbed through his own field guide to explain the evolution of this group to the several Papuan students gathered round. There are good reasons why the story of these spectacular birds illustrates so well the links between evolution, narrow ranges, and rarity.
Birds of New Guinea
indicates the tremendous variation in the most obvious traits of plumage color and size, as well as in less prominent features such as beak length and size of feet.

Evolution is not sorcery, but the transformation of a single bird of paradise ancestor into these forty wondrous variations is magical just the same. Biologists, though, use a different term for “abracadabra”—
adaptive radiation. This is the evolutionary phenomenon by which a number of species evolve from a single ancestor, often diverging to occupy different ecological niches and isolated geographic spaces. Genetic evidence shows that birds of paradise probably descended from a crow-like bird about 28 million years ago when the bird of paradise line split off from the ancestors of the crows (the so-called corvine assemblage that arose in the Australian region). In the absence of primates and other bird groups as predators, birds of paradise spread their wings, so to speak. They flew to new places and then changed in certain traits, often in the presence of and in competition with other resident species. Once reproductive isolation from members of their species they had left behind had been established in their remote mountain domains, they evolved to expand their diets in response to food sources available in their new homes, whether as fig eater, or bark chipper and grub extractor, or spider hunter, or miner of specialized fruit hidden in woody capsules of mahoganies and nutmegs. Some forms developed stronger legs to walk along tree branches and pluck fruits and insects, for example, while others developed short, weak bills and specialized in soft fruits. To apply the founding principle of natural selection: those that diversified in bill size or shape, and as a result fed more efficiently in their new habitat, invariably left more surviving offspring, while other variants over time passed from the scene.

Although the honeyeaters of the South Pacific rarely receive mention in the textbooks, they are another classic example of adaptive radiation in birds, with about 184 species descended from a single ancestor. The wattled smoky honeyeater hanging about Bruce's camp represented one of the newest species in the family. As we saw earlier, some isolated species, such as the Juan Fernández firecrown, remain rare, while a few, such as the green-backed firecrown, become transplanted or jump the ecological barriers and become abundant and widespread. Such shifts in rarity and abundance depend on a host of natural and human factors explored in later chapters.

During his daily searches, Bruce had begun tallying the number of birds of paradise he spotted or heard singing in the dawn chorus. By the second week in the Fojas, he had observed in miniature the general pattern of distribution in New Guinea. Some species, such as the two manucodes, the lesser and king birds of paradise, the riflebird, and the pale-billed sicklebill, were confined to the lowlands and foothills of the Fojas. Other species, including the bufftailed sicklebill and the several kinds of six-wired birds of paradise, restricted themselves to bands of forest at middle elevations. Still others, such as the black sicklebill that Bruce heard on the first day, holed up only on mountaintops. So it turned out that over time the birds of paradise had sorted by what biologists call altitudinal stratification. Perhaps some species were better than others at taking advantage of what nature gave them at different elevations and became further adapted to prospering in narrow elevational bands of forest. Above or below their particular elevational band, they might have been replaced by another species.

As a group, birds of paradise have no rivals—except perhaps the pheasants—and are the most beautiful birds in the world. There is widespread use of their plumage among New Guinea natives, who fashion headdresses of the feathers to wear at clan gatherings. Some clansmen prize the long enameled, pearly head feathers of the king of Saxony bird of paradise. Others go for the white, trailing plumes of the ribbon-tailed. Highly valued, too, are the iridescent blue breast feathers of the superb bird of paradise. Beauty and extreme rarity in New Guinea often coincide, with the result that some of these species have been wiped out in areas around villages. A Papuan ornithologist documented the carnage wreaked by such ornamentation, reckoning that about 36,000 birds had been killed to furnish headdresses for one clan gathering in one mountain town.

Each evening back at camp, the botanists also shared their discoveries. Tropical botanists often feel overshadowed on expeditions, perhaps because their quarry is stationary. Even if a spectacular
species is in flower or fruit, the display is ephemeral, unlike the headdress of the bowerbird or the pelage of the golden-mantled tree kangaroo. But here in the Fojas, botanists on the team came upon an eye-catching plant that rivaled anything found by the vertebrate chasers. It was a rare white-flowered rhododendron and featured the largest bloom on record for that genus, measuring almost eighteen centimeters across. (Wild rhododendron flowers are seldom more than six centimeters in diameter.) The flower came from a canopy-living shrub-like rhododendron that also appears as a shrub around bogs. Rhododendrons are common at high elevations, yet another example of adaptive radiation, this time in a common genus of shrubs, trees, and climbers. In all, New Guinea is home to about 164 of the nearly 850 species of the genus
Rhododendron
; most are found in the uplands, as in such places as the Fojas, where three unique species can be found.

The alpine zone above timberline in New Guinea's cordillera, including the Foja Mountains, is quite small compared with those of the Himalayas and the Andes, so the alpine plants endemic to this habitat would have very limited ranges. Robert Johns, one of the fathers of botanical research in New Guinea, estimates that there may be as many as 15,000 to 20,000 species of plants endemic to New Guinea and its outer islands, or about 5 to 8 percent of all vascular plants on Earth. About 70 to 80 percent of New Guinea plant species that are endemic have very limited ranges, most in the alpine zone. In contrast, the canopy tree species in the lowland rain forests have wide ranges. The most common ones share an affinity for the mainland tropical forests of peninsular Malaysia and the remnant rain forests of northeastern Australia.

Plants offer yet another perspective on the link between endemism and rarity on islands or other geographically isolated locales. Consider the plants on some more familiar islands: Puerto Rico, Jamaica, Hispaniola, Cuba, the Galápagos, New Caledonia, New Zealand, Hawaii, and even the Juan Fernández. Among all these islands, the Hawaiian chain, not the fabled Galápagos, has the
highest percentage of endemics. Hawaii has a flora of about 970 vascular plant species, with 91 percent found only on the islands. Right behind are New Zealand, with about 2,000 species and 81 percent endemism, and New Caledonia, with about 3,250 species, of which 76 percent are local. These three islands are in a class by themselves globally, along with aforementioned New Guinea. Then there are the Juan Fernández Islands, at about 200 native plant species and 62 percent endemism; Cuba, at 5,900 species and 46 percent; Hispaniola, at 5,000 species and 36 percent; and, bringing up the rear, the Galápagos, at 700 and 25 percent; Jamaica, at 3,250 and 23 percent; and Puerto Rico, at 2,800 and 12 percent. The explanation for this pattern of rarity among islands, using endemic plants as a rough indicator, would likely reflect distance from a mainland, topographic relief, variety of habitats, and in the case of continental islands, the age of the island since separation. On these islands, some of the endemic plants might be superabundant locally, not rare in number at all, though still rare by the criterion of range. Others are rare not only in range but also in number.

Other members of the expedition were concentrating on vertebrates other than birds. One evening the Kwerba guides reported a brief sighting of a golden-mantled tree kangaroo, one of the rarest mammals in New Guinea and one of the most uncommon in this group of marsupials.

The golden-mantled is a handsome six kilograms of silky chestnut-brown fur offset by light underparts and a yellow wash on the neck, cheeks, and feet. A double golden racing stripe runs down the back. The yellow and maroon furry tail is almost one meter long. The naturalists' find was the first sighting of this animal in the Indonesian portion of New Guinea and represented only the second known site of occurrence. Tim Flannery, a world authority on New Guinea mammals, first described this species in 1993; it had been sighted across the national border to the east, in Papua New Guinea.

We don't usually think of kangaroos hanging out in trees, but ten of New Guinea's native kangaroo species prefer an arboreal life.
Tree kangaroos will never match the acrobatics of monkeys or gibbons, but tree roos are nevertheless skilled leapers and skydivers, able to fall twenty meters to the ground without breaking a limb. Once on terra firma, tree roos lack the athletic grace of a wallaby or wallaroo, but they can still scamper at speed. The arboreal lifestyle, however, is a comparatively recent evolutionary move. Not unlike whales, whose ancestors were land mammals that headed back to
sea, tree kangaroos evolved from ground-dwelling kangaroos that in turn descended from arboreal opossums.