100 Under 100

by Scott Leslie

  Over 50 species of warblers—all belonging to the family Parulidae—inhabit the continent’s woodlands, most of them in the east. Some, like the yellow-rumped and the magnolia, are widespread and abundant; others—the endangered golden-cheeked and Kirtland’s warblers come to mind—are found only in very specialized habitats and are quite rare. Even these, however, can’t hold a candle to the Bachman’s warbler in the scarcity department.

  Last seen in Louisiana in 1988, Bachman’s warbler is possibly extinct but still listed as endangered under the US Endangered Species Act and critically endangered on the IUCN Red List. According to the US Fish and Wildlife Service, its current population number is unknown. That number, if it is anything other than zero, must be vanishingly small, possibly in the double or even single digits.

  The bird was first described in 1833 by John Bachman, a Lutheran pastor and naturalist from South Carolina. He sent skins of the bird to his close friend, John James Audubon. Although Audubon never saw the bird in the wild, he included a painting of it in his famous work Birds of America. Interestingly, the artist simply painted the pair of warblers into an original illustration of a franklinia bush by Maria Martin, Bachman’s second wife and one of the first female natural history illustrators in the United States. That Audubon never observed a living Bachman’s warbler is evident in the stiff poses of his painted birds, which contrasts with Martin’s exquisite rendering of the franklinia.

  Bachman’s warblers inhabit cypress swamps with an understorey of saw palmettos in the southeastern United States. Here they build their little cup-shaped nests of grass and Spanish moss in the canebrakes (stands of bamboo), brambles, and other undergrowth. Three or four nestlings are fed a diet of insects for a couple of weeks before they can fly on their own. At the end of the breeding season they migrate south to Cuba for the winter.

  The little yellow-faced bird with its black throat and cap, delicate down-curving bill, and a buzzing trill of a song has been somewhat of a mystery in the southeastern United States for the last two centuries. Early reports of its abundance were often contradictory: some said there were many, others said few. Perhaps it depended on whether birds were counted during migration, when their numbers tend to be concentrated, or during nesting season when they are spread out. In any event, the species apparently went missing for several decades during the 1800s, until a few dozen of them were shot by one Charles Galbraith in 1888, a hunter for the ignominious hat trade. (Back then, women’s hats were decorated not only with the exotic plumes of egrets but with stuffed whole songbirds. In fact, one of the specimens of the Bachman’s warbler in the American Museum of Natural History was literally plucked from a hat.)

  It wasn’t until 1897 that the first Bachman’s warbler nest was discovered, more than 60 years after being scientifically described by its namesake. Around the same time, the species stronghold appeared to be in the swampy woods bordering the lower Suwannee River in Florida. Since then, however, the population has plummeted. As early as the 1940s, Bachman’s warbler was the rarest songbird on the continent. In spite of its near absence for many decades, the species wasn’t listed as officially endangered until 1967.

  The cause of its decline is far from clear. Loss of cypress swamp forest seems to be only a contributing factor because there appears to be enough presumably good habitat left to support at least a few breeding pairs. The extensive destruction of the vast canebrakes of the southeast, in which the species is thought to nest, is also likely an important agent in the decline. Perhaps the clearing of forest to make way for sugar cane plantations where the species wintered in Cuba ushered it down the path of extreme rarity. Or maybe severe hurricanes killed off so many Bachman’s warblers during migrations that it became hard for survivors to find mates to breed with. On the other hand, if the bird has always been rare, its decline may have been inevitable in the face of human progress in the southeastern United States. The most likely cause for its precarious state is all of the above. The official nail of extinction has yet to be driven into the species’ coffin, however, since much of its nearly inaccessible potential habitat, such as the vast Congaree Swamp of South Carolina, hasn’t been fully surveyed. So there’s a very slim chance the bird may still exist.

  But is this just wishful thinking? Probably. Yet, in January 2002, a bird closely resembling a female Bachman’s warbler was videotaped in Guardalavaca, Cuba. Experts from the Cornell Lab of Ornithology later examined the video and pronounced it inconclusive—but found it intriguing enough to post on the lab’s website, with an invitation for further opinion on the evidence. The identity of the mystery bird in Cuba has never been confirmed.

  On an island in the Pacific, ornithologists are equally anxious to catch sight of another species whose continued existence is also questioned.

  MOLOKAI THRUSH

  Hawaii may be a Pacific paradise and the most isolated archipelago in the world, but it is struggling with the loss of its amazing biodiversity, especially birds. Dubbed the “extinction capital of the world” by conservation biologists, half of the state’s 140 known endemic bird species have already disappeared. Trouble in paradise began when the first Polynesians arrived about 1,600 years ago, long before the first Europeans set foot on the islands. The Polynesians killed the islands’ birds for food, and for their colourful feathers to be used as currency. What’s more, feathers decorated their ceremonial dress, most notably the raiment of kings, whose elaborate capes were festooned with tens of thousands of colourful songbird feathers. The robe of King Kamehameha the Great is said to have required nearly a half million brilliant yellow feathers from the O’o bird, now extinct.

  In 1779, Europeans brought invasive species such as goats, pigs, feral cats, rats, and even introduced bird species like cardinals and bulbuls. All have wreaked havoc on the native birds, which were not equipped to deal with aggressive mainland organisms. A third of all of the endangered birds in the United States are exclusive to Hawaii. Though native Polynesians may have exploited the birds pretty heavily, all bets were off for the future of the archipelago’s avifauna once Europeans colonized the islands.

  Their most insidious import was the mosquito. Hawaii was free of the pest until about 1820, when it arrived as an accidental stowaway on ships from the mainland. Unfortunately, the earlier release of domestic pigs into the islands’ forests produced perfect conditions for mosquitoes to really take hold. With an abundance of food, the pigs multiplied and became feral. Soon they were tearing apart the trunks of native tree ferns and creating cavities for standing water—perfect breeding places for mosquitoes, which would soon thrive. As vectors of deadly avian malaria, the pesky insects threatened the very survival of many native birds. Some escaped the insects by moving up the mountains to where it was cooler. But warming temperatures owing to climate change may soon render this strategy useless. And, as the islands’ human population has grown, ever more of the unique forest habitats so crucial for Hawaii’s birds have been destroyed for urban and agricultural development. This has pushed native species, already reeling from hunting by humans, introduced animals, plants, and disease, into an ecological corner.

  The ubiquitous American robin, a member of the thrush family, may be one of the most abundant birds in the world, but another member of the same family, also a resident of the United States, is among the rarest. The endemic brown and grey Molokai thrush (Oloma’o in the native Hawaiian language) is unusually drab for Hawaii, where most birds are brilliantly plumaged, like the state’s famous scarlet honeycreepers. What this thrush lacks in bright feathers, however, is made up for by its brilliant voice. Its song is remembered as a chorus of liquid, ventriloquial, flute-like notes, often sung all the day long and even through the night. Today, the gist of the Molakai thrush’s colourful music is preserved only in written records, since its song has never been recorded.

  The species was first listed as endangered in 1970, and the last confirmation of the bird’s existence was in 1980. Despite its long absence, it has
not been declared extinct, since there is still a small chance it survives—though habitat destruction and avian malaria have so devastated its population that if it does exist, the population would be tiny indeed. The only thing that can be done at this stage is to continue surveying for evidence of the species, restore its historically known habitats, and remove harmful invasive species. Realistically, though, there isn’t a whole lot of hope that the Molokai thrush will be found. And the status of a bird next door on the island of Oahu is every bit as tenuous.

  OAHU CREEPER

  Members of Hawaii’s creeper guild (a group of various bird species in a natural community using similar techniques to gather similar food types) are found only in the archipelago. Today, five separate species of Hawaiian creepers survive: one each on Hawaii and Kauai, both relatively common; one on Maui, endangered but with a population in the thousands; the extinct Molokai creeper; and the hairbreadth-from-extinction Oahu creeper.

  The theory of evolution tells us that every species does its own thing to survive. Sparrows hop along the ground picking up seeds and bugs, swallows swoop through the air scooping flying insects into their gaping beaks, and warblers flit about the forest canopy, picking insects off leaves. So it goes, each using its own proven method of getting a meal. The Oahu creeper’s name is a dead giveaway for how it gets a living: by inching up and down the trunks of trees, with its ear to the bark listening for unsuspecting beetle larvae underneath. Little is known about the 10-centimetre-long warbler-like bird, with its brilliant yellow belly and face and bright olive-green back. It remains largely a mystery. In addition to its distinctive foraging techniques, it’s thought to lay two eggs in a nest made of soft mosses and tiny rootlets. Its song has never been described.

  First discovered by science in 1850, biologists today are uncertain whether the Oahu creeper survives. Although its last confirmed record was on Christmas Day in 1985, there have been several more recent sightings in lowland native wet forest along the Poamoho Trail, in the island’s Ko’olau Mountains. These haven’t been confirmed, however, since the creeper is easily confused with the very similar amakihi, a more common Oahu species. But the understandable reluctance to declare the species officially extinct has delayed any such move until every last scrap of its potential habitat has been thoroughly explored.

  Some suitable creeper habitat still survives on Oahu—the largest piece a 1,500-hectare tract of native forest administered by the Nature Conservancy of Hawaii—so habitat loss doesn’t appear to be the sole reason for the species’ decline. It’s likely that the main culprit in the whole matter is avian malaria, the mosquito-borne disease that is responsible for the decimation of much of Hawaii’s bird life. On the US endangered species list since 1970, the bird also remains listed as critically endangered on the IUCN Red List.

  Like Hawaii, Amsterdam Island, home to the world’s rarest albatross, is one of the remotest islands in the world, with an ecosystem that is also being destroyed by invasive species.

  AMSTERDAM ALBATROSS

  The greatest travellers among earth’s creatures, albatrosses have been the embodiment of freedom for as long as humans have known them. Among seafarers they were synonymous with the wind, as immortalized in Coleridge’s “The Rime of the Ancient Mariner”: “For all averred, I had killed the bird / That made the breeze to blow.” Throughout history, sailors also believed that albatrosses carried the souls of their lost seafaring brethren.

  Few living things are as well adapted to live in the vast wilderness of the earth’s high seas, especially those in the southern hemisphere. On long slender wings evolved for gliding just above the water, albatrosses use air currents and updrafts formed when wind blows across the waves to carry them over vast distances with minimal flapping and maximum efficiency. During a lifetime—they can live up to 50 years—some species travel more than 16 million kilometres, or the equivalent of 50 round trips to the moon. One of these great wanderers may soon disappear.

  Found only on Amsterdam Island in the Indian Ocean, the Amsterdam albatross, with a wingspan of nearly four metres, is one of the largest birds on earth. It is also one of the rarest. Initially thought to be a subspecies of the wandering albatross, it was first described by science only in 1983. With its brown breeding plumage, the Amsterdam Island albatross is unusual among a family of typically white birds. The puffiness of the feathers covering the head, the large pink bill, and the jet-black eyes residing beneath a prominent brow give the bird an endearing puppet-like appearance.

  Nowhere in the animal world is there a more dedicated parent. Mating for life and bearing a single chick every two years, the Amsterdam albatross invests a great deal of effort into ensuring its offspring survives. Both parents participate in all aspects of its upbringing. While one adult stays with the young (the parents will alternate), the other embarks on a journey across 4,400,000 square kilometres of the southern Indian Ocean in search of food to feed the hungry, rapidly growing chick. This continues for seven months until the nestling takes its first flight. Once its feathers are fully formed, the young bird makes several awkward attempts to get airborne. To be fair to the neophyte bird, all albatrosses, seasoned adults included, are less than graceful whenever they’re leaving or landing on solid ground. They become airborne by running down a slope into a headwind to generate enough lift. Once in the air, young albatrosses fly out to sea, embarking on a journey of hundreds of thousands of kilometres around the southern hemisphere’s oceans. They won’t touch land again until they return to Amsterdam Island five years later, when they are sexually mature.

  Amsterdam Island is very remote. Only 55 square kilometres in area, it lies in the middle of the southern Indian Ocean, exactly midway between Africa and Australia. It is a testament to our planetary reach that a group of creatures so wide ranging in its oceanic peregrinations, so far flung from our own centres of population, is affected by human activities. In fact, although it is the most imperilled member of its family, the Amsterdam albatross isn’t alone in its struggle to survive: two-thirds of the two dozen species of albatross are today threatened with extinction. The major culprit for many of them is longline fishing, where high-seas boats tow long hooked lines heavily weighted with bait. For surface-feeding seabirds, such gear, loaded with tasty, attractive food, is irresistible—and deadly. The birds get snagged while trying to get the bait and subsequently drown as the line sinks. Some 100,000 albatrosses are killed this way every year. Although scientists think longline fishing has contributed to the dire situation the Amsterdam albatross finds itself in, other factors may be even more important.

  Except for a small research and military station (the island belongs to France), Amsterdam Island has never been permanently settled. That’s not to say it hasn’t been tried. One attempt, made long ago, marked the beginning of real trouble for the albatross. In the spring of 1870, a peasant family from the distant island of Réunion was left on Amsterdam with a few cows to establish an outlier cattle station. The family didn’t last long in the harsh environment and eight months later abandoned the island, leaving behind their livestock. Left to run amok across the uninhabited landscape with no predators and lots of grass to eat, the original population of a few cows grew to many thousands. The feral cattle stomped and ate their way through Amsterdam albatross habitat over the past century and a half, reducing its breeding range—and hence its population—on the island. Now the few birds left are relegated to a tiny area in a bog on the island’s central plateau that the cows can’t reach. What’s more, feral cats—the scourge of island birds everywhere—left behind by visiting ships over the decades have taken a toll on vulnerable albatross chicks.

  The number of cattle has been reduced to about 1,000 by an eradication program over the past two decades, and fences have been erected to keep the remaining ones out of the nesting area. As well, plans are in place to cull the feral cat population and to manage vegetation to enhance nesting habitat. However, this may not be enough. The Amsterdam albatross fa
ces a new, serious challenge in the form of deadly avian diseases that have been found infecting another seabird species on the island.

  When the Amsterdam albatross was described as a new species just over a quarter of a century ago, its entire known breeding population consisted of just five pairs. Today, its numbers have increased to about 80 mature birds (of which only 10 to 20 pairs will breed in any given year). Yet there is evidence that the newly discovered avian diseases may have already caused a decrease in chick survival rates. So, despite some success in restoring its numbers, scientists now fear the population may begin declining again. If true, and the disease has already taken hold, the future of this magnificent species just got a bit less certain.

  CHINESE CRESTED TERN

  Even a soaring albatross can’t surpass the grace and elegance of a tern in flight. As light as butterflies on the wing, 44 species of these slender, delicate creatures inhabit the earth. Found on every continent and sometimes mistaken for gulls, terns are generally white with black accents (a few, like the noddies, have all dark plumage) and are among the most abundant larger birds. Most migrate, a few incredibly so. One of them, the Arctic tern, migrates over a million kilometres in a lifetime—nearly enough to make it to the moon and back twice. By following the summer season to the alternating poles of the planet, it sees more daylight than any species. Thankfully, this champion traveller is still abundant. One migratory tern, however, may soon cease to see daylight at all, ever again. The Chinese crested tern, restricted to just two breeding sites along the east coast of China, is the rarest of its family and one of the most endangered birds on earth. White with light grey wings, a large head with a shaggy black crest, and a black-tipped yellow bill, the Chinese crested tern is also among the larger members of its family, growing to a length of 43 centimetres.