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Hawaii's Forest Birds Sing the Blues
by Howard Youth
It's no vacation for the islands' native birds and the people trying to save them. Species that thrived until humans arrived around 1,600 years ago now depend on wise management in the few oases in which they still hang on.
Hawaii is a great place to see exotic wildlife. Brazilian cardinals hop on the sidewalks. Wild pigs and mongooses from India track through the underbrush. Flocks of red-billed leiothrix, also known as Pekin robins, and orange-cheeked waxbills from Africa pop in and out of the trees. In many respects, you could call Hawaii a sort of resort for introduced species. But start looking for the Hawaiian Islands' most fascinating creatures--the native ones--and you may be literally looking for ghosts.
The remote Hawaiian Islands, which lie more than 2,500 miles from the nearest mainland, have the dubious distinction of being the site of some of the world's most amazing adaptive radiations--and some of its worst ecological devastation. Since humans arrived around 1,600 years ago, the islands' specially adapted native plants and animals have suffered. All told, 75 percent of documented floral and faunal extinctions in the U.S. have occurred in Hawaii. Of those that survive, 170 of its endemic plant species are listed as endangered (35 percent of the U.S. Endangered Species list of plants), many with 100 or fewer individuals left, and some in which only a single plant remains, according to a 1994 U.S. Fish & Wildlife Service (USFWS) report. Many unique invertebrates and fish are gone. And half of the islands' 140 historically recorded native bird species are extinct, while 31 of these remaining species are endangered (40 percent of the U.S. Endangered Species list of birds), according to a 1992 report issued by the USFWS, the Hawaii State Department of Land and Natural Resources, and the Nature Conservancy of Hawaii.
Hawaii's endemic birds have been the most visible sentinels of the sinking ark. Their detectability--distinctive calls, songs, and plumage--renders them extremely good environmental indicators, and the story of their struggle illustrates the ongoing fight to save Hawaii's remaining endemic species.
There is no single villain killing Hawaii's forest birds. "I call it a negative synergism," says Jack Jeffrey, wildlife biologist for the U.S. Fish & Wildlife Service (USFWS) at Hakalau Forest National Wildlife Refuge on the island of Hawaii. "The birds are being hit from all sides. It's hard for them to keep up." Jeffrey, along with state biologists and other volunteers and scientists from the Hawaii Audubon Society, the National Park Service, USFWS, The Nature Conservancy of Hawaii, and the National Biological Survey, helps census some of the islands'--and the world's--rarest birds.
"It's safe to say the amakihi [a honeycreeper species] and Hawaiian hawk don't seem to be declining--everything else is pretty much in a tail spin," says Reggie David, president of the Hawaii Audubon Society. Disease, habitat destruction, and introduced plant and animal species all play a part in the decline of most of the islands' living endemic birds. A dozen endemic species hover on the brink of extinction, with fewer than 100 individuals left, some of these have not been detected at all in recent years.
Origin of the Species
Of Hawaii's birds, the honeycreepers (Drepanidinae) are most famous, having put on what is arguably the world's most dazzling display of adaptive radiation--an explosion of species from a single unspecialized ancestor to at least 54 species that filled available niches in the islands' habitats. In fact, speciation in the Hawaiian honeycreepers dwarfs the famed radiation of Darwin's 14 Galapagos finches.
Robert Fleischer, Cheryl Tarr, and Carl McIntosh at the National Zoo's Molecular Genetics Laboratory estimate that the honeycreepers' ancestor arrived three to four million years ago; others put the arrival farther back, at closer to seven million years ago. This ancestor--one colonizing species of finch, possibly a Eurasian rosefinch (Carpodacus sp.) or, less likely, the North American house finch (Carpodacus mexicanus)--started what proved to be an evolutionary snowball. "There must have been a lot of open niches, and the birds hit the islands and speciated very rapidly," says Fleischer, who studies the genetics of fossil and living Hawaiian birds. Rapidly, in terms of geologic time, is thought to be within the first 200,000 to 300,000 years after the first finch touch-down.
Nectar-feeding honeycreepers evolved dramatically curved bills designed for probing and extracting the nectar from the flowers of Hawaii's endemic lobelias and other plants. Insectivorous honeycreepers developed thin, warbler-like bills for picking insects from the foliage. Seed-eaters developed stouter, stronger bills for cracking tough husks. Some species probed or cracked bark with strong hooked bills seeking wood-boring insects, thereby filling a niche woodpeckers do elsewhere.
Honeycreepers shared the islands with an array of other unique bird species. In 1991, Storrs L. Olson and Helen F. James of the Smithsonian's National Museum of Natural History described for the first time 32 extinct species they identified from bones found in lava tubes, sinkholes, dunes, and excavated Polynesian refuse piles (middens) on the main Hawaiian Islands over the past 19 years. Three others had been previously described. When their analyses are through, at least 20 more species will likely be added.
These recent findings conjure up a vision of an almost mythical world where birds, not mammals, dominated. Large flightless waterfowl called moa nalos were the islands' large herbivores. A harrier, a hawk, an eagle, and four owls topped the food chain as predators. No mammals patrolled the ground (Hawaii's only native land mammal is a bat), and, with the need to fly gone, many of the castaway bird species, such as endemic ducks, ibis, and rails, lost their powers of flight.
But splendid isolation left Hawaii's flora and fauna ill-equipped to deal with the arrival of humans, and, as on most other isolated islands, endemic species quickly disappeared, or declined, once Homo sapiens hit the shores and wiped out flightless and ground-nesting species
Raiders and a Lost Ark
Polynesians arrived in the Hawaiian Islands as early as 300 A.D., bringing with them agriculture and a need for meat. Contrary to previous belief, these first settlers did not live in complete harmony with nature, though in many instances they did manage native resources better than the Europeans, who arrived much later. Soon after their arrival, Polynesians slashed and burned the islands' lowland forests to plant extensive fields of sweet potato and taro. They, their dogs, and pigs and Polynesian rats (Rattus exulans) they introduced, hunted the islands' flightless and flying birds or raided their nests. Countless small honeycreepers were killed so their red and yellow feathers could adorn rulers' feather robes and headdresses--80,000 birds of one now-extinct species (Drepanis pacifica) were sacrificed to make one of King Kamehameha I's cloaks in the late 1700s.
Pressures on Hawaii's habitats, flora, and fauna grew as the human population expanded to between 300,000 and one million by the 1500s. Before Europeans set foot on the islands, most of the forests--even scattered trees--below 3,000 feet had vanished, and the 55 or so bird species Olson and James have described from fossil records had been wiped out.
In 1778, Captain James Cook's third voyage landed him in Hawaii, marking the first arrival of Europeans, who dealt the next blow to Hawaii's birds and native species. Goats, cattle, sheep, and more pigs arrived with Cook and with Captain George Vancouver in 1794. Norway (Rattus norvegicus) and black rats (Rattus rattus), common ship stowaways, came ashore.
By the time Europeans arrived and began to settle in Hawaii, most native lowland forest birds had already disappeared along with their habitat, and settlers grew anxious for winged companions. Andrew Berger, in his book The Exotic Birds of Hawaii, quotes an ad in a 1860 newspaper that read: "Owners of vessels leaving foreign ports for Honolulu will confer a great favor by sending out birds....We need more songsters here." Some early releases included common pigeons (Columba livia) in 1796, common mynas (Acridotheres tristis) in 1865, and the honeycreepers' close relative, the house finch, before 1870. All told, 160 species--at the very least--have been introduced, of which at least 50 have established breeding populations somewhere in the state.
In 1826, the whaling ship Wellington, in from San Blas, Mexico, brought Hawaii its first mosquitoes, which were dumped ashore as the sailors rinsed out water barrels. Some of these insects (Culex quinquefasciatus) carried avian malaria and pox, diseases Hawaii's native birds were not genetically equipped to cope with. An epidemic began among the nonresistant native birds. Similarly, the European settlers' arrival also brought human diseases--pneumonia, smallpox, syphilis, and others--that knocked the Polynesian population down to below 195,000 by the early 1800s.
Mongooses were introduced in the 1880s to quell the rat invasion, but they focused instead on hunting the remaining ground-nesting birds and their young. Goats and cattle set their sights on vegetation. All the trampling, rooting, grazing, and browsing, along with deforestation by humans, left a devastated landscape. At least a dozen more species have gone extinct since European arrival.
Today, half of the islands' rich rainforest--and about two-thirds of its total forest cover--is gone. Habitat destruction and invading exotics, particularly the Culex mosquitoes, left many species hanging on only in the wetter, more remote parts of their original ranges. "In many cases these [Hawaii's surviving native forest species] are birds known to have occurred in drier parts of the islands--wetter habitats may have been marginal for them even in the best of times," says Alan Holt, director of science and stewardship for The Nature Conservancy of Hawaii.
Today, exotic immigrants continue to be shuttled in on regularly arriving flights and shipments. "The biggest problem Hawaii faces is the continuing flow of new species into the islands," says Holt. "It's also the number-one threat to Hawaiian agriculture and tourism." At least 12--and as many as 35--new exotic invertebrate species arrive in the islands each year, according to the Hawaiian Entomological Society. Holt fears the actual number is higher. Of these, about five per year prove to be nuisances, says Holt, while about one a year becomes a major economic pest, like the lesser cornstock borer (Elasmopalpus lignosellus), which arrived in the late 1980s and has destroyed sugar cane crops and cost about $9 million in research and control efforts, and the Formosan termite (Coptotermes formosanus), introduced in the early 1900s, which causes $50 million in damages to buildings each year.
Clouds of biting flies or intertwined masses of snakes are some potential introductions that could frighten off prospective tourists. The effects of already established populations of exotic ants and predatory wasps on native insects, and of competition between introduced honeybees and nectar-feeding birds, have not yet been thoroughly studied, but they are likely to be substantial.
Foreign flora also have found new avenues onto the islands, especially where habitats have been disturbed. Especially resilient invaders include blackberry (Rubus argutus), gorse (Ulex europaeus) from mainland Eurasia, South American lantana (Lantana camara), strawberry guava (Psidium cattleianum) from Central America, and the South American banana poka vine (Passiflora mollissima), a passion fruit that has blanketed more than 70,000 acres of native forest. About 4,500 plant species have been introduced since European arrival, including virtually all the plants tourists encounter in resort areas. "Most of our weeds are not pests in the countries they come from," says Holt, who adds that the species thrived "in paradise" without the natural limiting factors, such as the cold spells or insects, present in their native lands.
The most frightening potential immigrant could be the brown tree snake (Boiga irregularis), a species that found its way to Guam, possibly on scrap metal shipments from New Guinea after World War II, and has literally eaten 9 of its 11 endemic bird species out of existence since 1975. Recently six snakes turned up at Honolulu Airport and the nearby Hickam Air Force Base, stowaways on some of the daily flights that arrive there from Guam. The species is nocturnal, arboreal, and elusive, and "unless it's in really high densities, the chances of detecting it are slim," says Hawaii Audubon's David. Airport officials are keeping an eye out for the up-to-eight-foot-long snakes, which, aside from killing birds, have a mild poison that can cause human infants respiratory problems if they're bitten. Further, brown tree snakes crawling into utility boxes have cost Guam's local utility company millions of dollars in damages and weekly power outages.
It is likely that more of the stealthy reptiles will arrive in Hawaii. Research on a virus that might knock out the brown tree snake on Guam--and Hawaii, if it colonizes the state--is being conducted by Donald Nichols and his colleagues at the National Zoo's Division of Pathology. The snake's sociable tendencies may prove to be its undoing on Guam if an effective pathogen can be found. "These snakes are fairly gregarious and often hide together in groups during the day," says Nichols, who notes that many other snake species are solitary. So far, six different viruses have been tested under laboratory conditions and two of these have been found to cause around 50 percent mortality. But immune systems and viruses are constantly changing, so if a virus with the desired effects is found, it will have to be rechecked regularly and refined to be kept effective.
The Alien Species Action Plan (ASAP), a collaborative control effort between the state and U.S. departments of agriculture, the state forestry and wildlife division, U.S. Customs, the National Park Service, and more than a dozen other private, state, and federal organizations, kicked off in April 1994. In November 1994, a ten-point action plan went into effect that coordinates the efforts of the members to, among other things, develop a central hotline for reporting pests, work to increase public awareness of exotic-species issues, get all airlines flying into Hawaii to show an in-flight video educating passengers about the pest problem, and ensure that thorough inspections of incoming flights from Guam continue.
Malaria and the Pox
The most dangerous pest to Hawaii's birds right now is the Culex mosquito. While exotic birds like the Japanese white-eye (Zosterops japonica), released in 1929 and today one of the most common birds on the islands, compete with native forest birds, the sharp declines in many native species stem not from competition with other birds but from a lack of resistance to avian malaria and pox carried into their habitat by Culex mosquitoes. "There are absolutely beautiful ecosystems at 2,000 to 5,000 feet that are [now] devoid of native birds," says the National Zoo's Fleischer.
Culex mosquitoes proliferate during wetter times of year and bite birds while they sleep. In Hawaii, they thrive in wet forests up to about 5,000 feet, where it starts to get too cool for them. It seems no mere coincidence that the highest rates of disease recorded have been around that altitude, where native species mingle with mosquitoes. In the lowlands, where resistant exotic birds now predominate, rates of infection are low in exotics but high on the native amakihi, the only native forest bird that is still doing well at lower elevations.
Although the dynamics of avian malaria and pox in Hawaii are still poorly understood, many think the mosquitoes are carrying the diseases to higher elevations. A 1993 study by the Madison, Wisconsin-based National Wildlife Health Research Center (NWHRC) reported infected birds at elevations as high as 5,200 feet. Jeffrey reports that malaria and pox have been found in birds up to 6,200 feet where he works, and larvae have been found at 6,000 feet. "Ten to twenty percent of the birds on the refuge at the highest elevations now have malaria and pox," he says, citing a 1993 study by University of Hawaii researchers working in the Hakalau National Wildlife Refuge.
The NWHRC study looked closely at birds in mid-elevation (around 3,900 feet) wet forest, and found that while many native species were infected, few of the mostly resistant exotic species were, "supporting the idea that native species are the primary reservoirs for infection with these diseases." But the study also suggests that some native species may be developing resistance: Experimental infection of the i'iwi, a honeycreeper disappearing from mid-elevation forest, proved "virtually 100 percent fatal," but about half of the tested apapane and amakihi, honeycreeper species still thriving in mid-elevation habitat, survived. The National Zoo's Rob Fleischer and Susan Jarvi are currently studying the genetic background of this resistance by focusing on a group of genes called the major histocompatibility complex (MHC), which helps dictate the immune response.
Not Well Enough Alone
The endemic forest species that hang on today--the Hawaiian hawk, 23 or so honeycreepers, several thrushes, one crow, a flycatcher, and a warbler--are vestiges of Hawaii's past living in fragments of Hawaii's original habitats. Much of these species' remaining woodland habitat is in government hands, being managed as national park or wildlife refuge or as part of the state reserve system. Other large areas are under private ownership, such as the 11 preserves managed by The Nature Conservancy of Hawaii, which encompass 23,000 acres, most of which is forest-bird habitat.
But many of the troubles facing the birds know no boundaries, and setting aside land is not the only necessary solution. "Just preserving habitat is not the answer in Hawaii," says Rob Fleischer. "There are a lot of problems that require active management." Such management costs money, and there is precious little of that to go around these days. The lack of resources, however, is being made up for by the sheer dedication of a handful of people.
The grueling exercises necessary to maintain Hawaii's natural habitats have become daily routine for the staff of the largest USFWS refuge in the main Hawaiian Islands, Hakalau Forest National Wildlife Refuge. The recently expanded (by about 16,000 acres) federal property on the island of Hawaii spans more than 32,000 acres, most of which is rainforest and higher-elevation pasture created years ago by cattle, which ate the forest understory, compacted the soil, and scraped off tree bark until the trees had fallen and died.
"We've [the refuge] just doubled in size but didn't double our staff," says Jeffrey, who, as the refuge's only designated wildlife biologist, makes up one-ninth of the refuge's work force. The maintenance workers and Jack must work constantly to keep introduced forces at bay. Constant maintenance of fences that keep out cattle and pigs from surrounding lands is one never-ending task that ensures that another--the replanting of native vegetation--is successful.
"But fences don't affect weeds, disease, or competition by exotic birds," points out Jeffrey. A finger of state land, managed for pig hunting, pierces the refuge and provides a corridor for the rampant banana poka, which staff must remove manually because herbicides would harm the native vegetation the vines creep over. Then there are the spiny gorse plants that crowd the pastures that Jack and his colleagues are trying to reforest. The gorse and blackberry, both introduced, are controlled with herbicides. Control is tough, eradication near impossible--a gorse seed, for instance, may remain viable for 30 to 40 years, according to Jeffrey.
The staff at Hakalau is working hard to stack the odds in favor of native species by reforesting the refuge's upper slopes with fast-growing koa (Acacia koa) trees, which create a shaded understory that would choke out exotic pasture grasses and encourage the return of other native plants. A state-run facility currently nurtures the plants from seed, but does not have the greenhouse space to raise the slower growing ohia (Metrosideros collina) and other native species the USFWS also wants to plant. Jeffrey and the rest of the staff are hoping for funds to build their own greenhouse soon.
Although cattle have pretty much been eliminated from Hakalau, pigs remain a threat to the plants and birds on the refuge, and other parts of the islands, and require constant control if the integrity of native habitats is to be maintained. "You have to take out 70 percent per year of the existing population of pigs to effect any control," says Jeffrey, "but the idea is to effect complete removal."
Why all this effort to remove pigs from rainforest? Although they are furtive beasts in the wild, swine continue to be among the greatest threats to Hawaii's habitats. For one, they serve as walking exotic plant dispersers. "Pigs carry weed seeds in their guts and spread them around with fertilizer," says Jeffrey. They also root through fragile native vegetation and indirectly spread avian malaria and pox by digging wallows and knocking over native tree ferns, eating out the plants' hearts, and leaving water-collecting stumps that provide breeding sites for the expanding Culex mosquito population.>
How do the dedicated scientists and conservationists who have committed themselves to the uphill battle to save Hawaii's natural heritage keep their chins up? Many of them have the gift of myopia and can often escape the gloomy big picture by narrowly focusing on their fascinating work. For example, entomologists will be busy for a long time grappling with the intriguing genetics of Hawaii's 800 or so species of tiny Drosophila fruit flies. And a Harvard biologist found in 1983 that the native Hawaiian ieie vine (Freycinetia arborea), once pollinated by several now-extinct bird species, is now pollinated primarily by the abundant Japanese white-eye. In turn, the exotic banana poka vine is now being pollinated by native honeycreepers. The natural history of Hawaii, though changing, remains enthralling, and scientists and conservationists remain intent on finding ways to sustain native species into the future.>
Meanwhile, federal, state, and private bodies are hard at work monitoring the problems and trying to protect remaining habitats. "We're protecting our little postage stamp out here," says Jeffrey of the ongoing work at Hakalau, which is just one of eight national wildlife refuges (total of 34,550 acres) and two national parks (total of 237,794 acres) on the islands. The state has set up strong zoning to protect watersheds and native species within its own extensive reserve system. The state owns about half of the islands' one million acres of forested land, and manages 110,000 of these acres within the 19 reserves that comprise its strictly managed natural area reserve system.>
There is constant concern about support for conservation. "Whenever funding or political commitment lags, forests have suffered," cautions The Nature Conservancy's Holt. But he adds that, for now, support remains strong. The Nature Conservancy of Hawaii, aside from managing its own sanctuaries, works closely with government agencies to pool resources and promote public support for conservation.>
Help has also come from New Zealand, which has seen similar natural history nightmares played out on its endemic species (12 bird species and subspecies extinct; 16 more endangered). Scientists in Hawaii have long shared information with those in New Zealand, but recently they've started visiting each other to compare horror stories and talk about solutions face to face. In 1992, Alan Holt and Mike Buck, the administrator of the Hawaiian Division of Forestry and Wildlife, traveled to New Zealand to establish an ongoing professional exchange program. In 1993 and 1994, experts from the two areas teamed up on projects focused on weed control, rare bird protection, feral animal control, and alien species prevention. >
Hawaii remains a wonderful living laboratory for scientists and naturalists. One of the world's farthest-flung cradles of diversity has taken some hard hits, but there is still a lot worth saving--about 10,000 endemic life forms, according to Nature Conservancy of Hawaii's Holt. Although humans have been behind massive extinctions in Hawaii, we now remain the only hope for those species that hang on in the paradise that is our fiftieth state. >
(ZooGoer 24(1) 1995. Copyright 1995 Howard Youth. All rights reserved.)>