Endangered Species Handbook

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It's Too Late

Bird Extinctions

      A bleak picture has emerged, showing a dramatic rise in the rate of bird extinctions over the past 200 years.  At least 157 species of birds have become extinct since 1500, and many more have not been seen in decades.  In pre-history, approximately one bird disappeared each century (Leakey and Lewin 1995), but the present rate is many times that.  During the 17th century, 15 birds disappeared, increasing to 26 birds in the 18th century (at an average rate of about one bird every four years); this was 26 times the pre-history rate.  Nineteenth century extinctions totaled 56 bird species, or about a bird every other year.  Data for the 20th century is still being totaled, but 54 birds have already been declared extinct since 1900 ‒ already almost as many as the entire 19th century’s toll.  Thus, the rate of avian extinctions has likely more tripled since the 18th century.  A large number of birds have not been seen in the wild for many decades and will likely soon be declared extinct; a period up to 50 years between the last sighting and formal declaration of a species' extinction is generally accorded, unless thorough surveys verify the species is indeed gone.
 
     An important dimension of these extinctions is the fact that birds are considered indicators of the planet's health.  Birds are sensitive to environmental pollution, habitat loss and other signs of deterioration, as illustrated when canaries were used by coal miners to test for the presence of lethal methane gas.  Their extinctions will also affect the ecosystems in which they once lived, since many birds pollinate plants or disperse seeds, and without them, these plants die off.  The story of the dodo (Raphus cucullatus) is an example of such a relationship.
 
      Some of the most amazing and unusual species that ever lived are among the birds that have become extinct since 1600.  Many of these extraordinary birds evolved on remote islands without human inhabitants over periods of millions of years.  The heaviest bird ever to have lived on Earth was the Great elephant bird (Aepyornis maximus) of Madagascar, the last of many related species of elephant birds.  Some experts maintain this giant bird disappeared prior to 1500 (Brooks 2000), but observers spoke of its continued presence on the island after 1600.  The giant moas of New Zealand are thought by some to have persisted until the 19th century, while others believe they died out a thousand years ago, within a few centuries after the arrival of the Maori people.  The brawny great moa (Didornis torosus) of New Zealand was perhaps the last of many species of moas, the largest of which was the tallest known bird, some 12 feet in height.  It was hunted to extinction like its relatives.  Some said it persisted until 1670.  Another extraordinary New Zealand bird was unique in that males and females had beaks that were completely different in both size and shape: the colorful huia (Heteralocha acutirostris) became extinct early in the 20th century, mainly from the effects of forest destruction and hunting for its feathers, which were sold in the European markets for ladies' hats. 
 
     The Mascarene Islands, which remained uninhabited by humans until the 17th century, once had an unparalleled diversity of birds, including an array of many odd flightless birds such as the famous dodo.  Flightless herons and storks fished in the streams, and enormous parrots ‒ their beaks as large as their heads ‒ lumbered about in search of fruits and seeds.  Each island had its own distinctive parrot species.  Some of the native parrots had not become flightless, and each of the seven or so species occupied its own ecological niche.  Gray parrots with bright red beaks, small gray parakeets and two types of lime green parrots with very long tails swooped about in large flocks (Fuller 1987). 
 
     Large numbers of the flightless, turkey‑sized dodos waddled about on Mauritius.  The birds, weighing about 50 pounds and covered with grayish, downy feathers, fed on hard-shelled seeds.  Of all birds that have become extinct, this species is perhaps the most famous.  The dodo’s common name apparently came from “dodoor,” a Dutch word meaning sluggard, and dodaers, a lubber, or awkward sailor (Halliday 1978).  The creature's original scientific name was Didus ineptus, indicating its inability to flee humans or defend itself. 
 
     In fact, the dodo was the final result of thousands — perhaps millions — of years of evolution in isolation on an island with no land predators.  Wild pigeons of an unknown species landed by chance on Mauritius at some early date and became resident, gradually evolving into a gigantic form of the original immigrant.  The dodo may have evolved from New Guinea and Pacific Islands tooth‑billed pigeons that landed in the Mascarenes, according to some zoologists (Halliday 1978).  Tooth-billed pigeons also have curious hooked beaks, although the dodo's 9 inch beak was far more massive.  Yet whatever its ancestry, the dodo became flightless in its predator‑free environment.  Its feathers lost their sheen and aerodynamic quality and came to resemble the down of nestling birds.
 
     Mauritius was first visited in the early 16th century by Portuguese sailors, and was later settled by the Dutch, who brought pigs, goats and cattle.  These domestic animals soon multiplied and overran the islands.  Pigs rooted in forests, devouring rare flora, and cattle and goats overran the fragile tropical vegetation.  Rats swam from ships and colonized the main islands; they preyed on flightless birds, eating their eggs and young, even climbing trees to devour nesting songbirds.  Mongooses native to Asia were brought to Mauritius, which presented a lethal threat to native birds and other wildlife.  Long-tailed macaques (Macaca fascicularis) were imported as pets at some point from Southeast Asia and then released into the forests of Mauritius, spreading throughout the island and preying on native birds.  Settlers also cut the trees needed by native birds for habitat and food.  The delicate plants, forests and vulnerable wildlife were devastated by this onslaught.
 
     Portuguese and then Dutch seamen and colonists slaughtered thousands of dodos, using them as a major source of food.  They cut down the seed-bearing trees dodos fed upon, and their eggs and chicks may have been preyed on by rats and introduced macaques (Fuller 1987).  Settlement began in 1634, and within less than 30 years, the once-common dodos were slaughtered to extinction.  The settlements failed and Mauritius remained uninhabited for a period of time.
 
     The last account of wild dodos dates from 1662.  A Dutchman named Volquard Iversen was deserted on Mauritius soon after both the early settlement and the penal colony failed (Quammen 1996).  Iversen and his shipmates scoured the island for food and found no dodos, but they did see some on a small islet off the coast.  He described them as "larger than geese but not able to fly. Instead of wings they had small flaps; but they could run very fast" (Quammen 1996).  The islet protected the last few dodos from human hunters and introduced predators, and until then, the tiny population had remained undetected.  Iversen's party waded through the shallow water to the islet and captured a dodo.  "When we held one by the leg he let out a cry, others came running forward to help the prisoner, and they were themselves caught" (Quammen 1996).  These were the last of their species.  Altruism, a trait that has helped many animals survive through mutual aid, has also caused extinctions.  Human hunters have taken advantage of this, killing animals that come to the aid of each other.
 
     In the centuries since its demise, the dodo has come to symbolize extinction, but many still think of this bird as stupid, giving rise to the expression "dumb as a dodo."  Animals are frequently deemed stupid if their natural defenses against humans are inadequate, or vicious if they are able to defend themselves.  Yet this bird so many people have described with disdain came to the rescue of its fellows, even at the risk of its own life, and was an extremely successful species within its environment.  If the word dodo must be seen symbolically, then it would be more reasonable to equate it with human stupidity, because our own species wantonly destroyed this extraordinary bird.  In the opinion of Errol Fuller (1987), author of the authoritative book Extinct Birds, "The dodo was one of the most fantastic creatures ever to have lived."
 
     In 1973, Dr. Stanley Temple, an ornithologist, made a remarkable discovery about the dodo.  He noticed that a beautiful tree native to the island, the calvaria or tambalacoque tree, was reduced to 13 dying specimens, all more than 300 years old.  Gerald Durrell (1977) described these trees as at least 50 feet tall, with massive crowns and silvery, gnarled trunks; cracks appeared in their buttress roots.  Since no young trees were located, it occurred to Dr. Temple that no seeds had germinated since the 17th century when the dodo became extinct.  Apparently, stones found in the dodo’s gizzard by sailors butchering it for food might have been able to abrade the thick shell covering the seeds.  Dr. Temple fed some of the seeds to domestic turkeys, which were presumed to have similar digestive systems, and of 10 seeds recovered from feces or regurgitation, three sprouted when planted (Anon. 1978). 
 
     Some scientists now believe this tree could germinate without the dodo.  A surviving parakeet is thought to be able to crack its hard-pitted seeds, and the extinct Mauritius flying fox and some of the extinct parrots were able to do so as well(Quammen 1996).  Dr. Wendy Strahm, in her botanical work on Mauritius, has found young trees of this species that germinated in the past 300 years, although they are quite rare (Quammen 1996).  Another scientist, Anthony S. Cheke, believes seed germination has continued, but at a low rate ‒ perhaps too low to maintain the species long-term. The rarity of the tambalacoque tree was considered to be due to seed predation by rats, deer browsing on saplings, rooting by pigs and perhaps browsing by the introduced macaque monkeys (Quammen 1996).  Yet dodos were likely major seed distributors of this tree in the pre-human environment, and their role has not been successfully replaced ecologically.  The introduction of a veritable zoo of non-indigenous species has reaped havoc on a variety of native plants. 
 
     The dodo's close relatives on neighboring islands are far less known. On Reunion, a bird called the Reunion solitaire (Raphus solitarius) was described by early visitors to the island as resembling the Mauritius dodo, except its beak was somewhat smaller, its plumage was white and the tips of the wings and the tail were black (Fuller 1987).  One traveler, M. Carre, said in 1699:  "The beauty of its plumage is a delight to see. It is of changeable color which verges upon yellow" (Fuller 1987).  Two were taken aboard ship as a present to the French king, but both refused to drink or eat and soon died.  M. Carre noted in his description that "The flesh is exquisite; it forms one of the best dishes in this country, and might form a dainty at our tables" (Fuller 1987).  This was an ominous prediction of its final fate.  The Reunion solitaire probably died out about 1715 as a result of being slaughtered for food.
 
     On tiny Rodrigues, yet another dodo-like bird existed.  Far more is known of this species, whose bones have been found in caves on the island. Its beak was shorter and its neck was longer, but it also apparently evolved from pigeon ancestors (Halliday 1978).  It was called the Rodrigues solitaire or solitary (Pezophaps solitaria) for its habit of feeding alone on leaves and fruit in secluded places.  Errol Fuller's description in Extinct Birds evokes its once peaceful existence: "In this tranquil kingdom generations of solitarys must have lived enjoying extraordinary peace and seclusion until their world was shattered by the coming of man." 
 
     Francois Leguat, a Huguenot refugee, left extensive descriptions of these birds when he spent two years on Rodrigues after he was marooned there with a small group of followers in 1691 (Fuller 1987).  "They walk with such stately form and good grace," Leguat wrote, "that one cannot help admiring and loving them" (Fuller 1987).  He watched them nesting and feeding their chicks until they fledged at several months.  The male and female defended their territory, driving other solitaires away with a dramatic display in which a bird pirouetted for four to five minutes while whirring its wings violently to produce a loud rattling noise that could be heard 200 yards away (Halliday 1978).  If this impressive display did not frighten other birds away, they used knobby growths at the joints of their flightless wings in combat with other solitaires (Halliday 1978).  Some wing bones now found in museums have healed fractures, an indication of the violence of these encounters (Halliday 1978).
 
     Leguat saw the parents of solitaires escorting their single chick to a gathering of some 30 other solitaire families, where the adults would leave the chicks.  Tim Halliday wrote in Vanishing Birds (1978) that he believes what Leguat witnessed was actually a sort of nursery gathering, similar to that which flamingos and some penguins organize while adults go off to feed.  Although these birds were able to hide in foliage and could run quickly, hunters chased them down and butchered every last bird.  People slaughtering them found stones in their gizzards ‒ even in those of very young nestlings.  How they got there remains a mystery, since the stones were too large to have passed down the gullet (Halliday 1978).  The last solitaire was seen around 1746, and the species was deemed extinct by the 1760s (Brooks 2000).
 
     The origin and affinities of these three species of pigeon-like birds in the Mascarene Islands will be disputed by scientists for some time to come.  Tim Halliday (1978) conjectured that the dodo may have evolved from a pigeon, such as the tooth-billed pigeon (Didunculus strigirostris) of the Pacific ‒which has a similar but far smaller hooked bill ‒ or that they were related to rails.  It is also possible the dodo had one ancestor and the solitaires had another.  What is not disputed is that they left no close relatives. No living birds on Earth are related to the dodo and the solitaire, or bear any strong resemblance to them.
 
     Other flightless native birds of the Mascarenes disappeared as well: all the huge parrots, three kinds of owls, three rails, several small pigeons, two night herons, a stork and an ibis.  Little is known about many of these birds, but two of the rails were described in detail.  The Rodrigues or Leguat's rail (Aphanapteryx leguati) had bright gray plumage flecked with white and gray, a curved red bill, red legs and feet and a red ring surrounding the eye (Taylor 1998).  The bird’s call consisted of a long whistle, but when pursued, the rail gave an alarm call that sounded like a person with a hiccup (Taylor 1998).  This species fed on tortoise eggs and, like the related Mauritian red rail (Aphanapteryx bonasia), could be lured by holding out a red object and trapped when the bird came to attack the lure (Taylor 1998).  They were described as delicious, and were killed to the last bird.  Among flighted species lost were a type of weaver, a starling and a falcon (Brooks 2000; Fuller 1987; Greenway 1967).  The total of 31 extinct birds is more than that of any other island group or continent.
 
     However extraordinary such a toll may seem for a group of small islands, it may represent only a percentage of Mascarene avian extinctions.  Stanley Temple estimated that prior to the arrival of humans, 68 species of birds lived on the three main islands and, of these, 45 species (66 percent) became extinct after 1600 (Temple 1981).  The 14 species not officially included among the extinct birds of these islands were described by travelers but have not yet been authenticated.  The majority lived on Mauritius.  Future archeologists are certain to discover far more about the birdlife that once inhabited these islands, and genetic studies of specimens from which DNA can be extracted may help identify their origins.
   
     The Hawaiian Islands vie with the Mascarenes for numbers of extinctions.  At least 21 species and many more subspecies have become extinct since 1600.  One of these was native to the remote swamps of Kauai.  The Kauai Oo (Moho braccatus) had pitch black plumage brightened by several long, canary yellow feathers.  The male had a haunting, fluted call.  The species dwindled as forests were cut, and by 1960, only 12 birds were known to remain.  A single pair survived by the 1980s.  The female disappeared after a hurricane in 1985 (Brooks 2000), and the male lived on a few more years as the last member of his species.  He was seen singing and building a nest with each final year, trying to attract a mate who never came (Daws 1993).  He was last seen in 1987 (Brooks 2000). 
 
     The Kauai Oo was the last of a group of dramatic songbirds that once lived on all the major islands.  The Hawaiian honeycreepers found only here evolved from one or a small number of ancestor species ‒ likely a New World finch, warbler or honeyeater ‒ into an estimated 40 to 50 brilliantly colored birds, before the arrival of the Hawaiian people.  Some species were probably eliminated after they were killed in tremendous numbers for their feathers, then made into elaborate headdresses and cloaks for Hawaiian royalty, but the major cause of their extinction was the destruction of their forests by European settlers.  As the honeycreepers retreated to smaller and smaller habitats, often surrounded by ranchland, sugar cane and pineapple farms, their habitats and food trees disappeared.  Their fragmented populations were susceptible to avian malaria, which spread throughout the islands in the 20th century, brought by exotic cage birds that had escaped or been released by their owners.  Thousands of birds died of the disease.  The extinction toll of native birds within the past few hundred years stands at 21 species, in addition to even more subspecies. Twenty-three honeycreepers survive, but most are so endangered they are not expected to survive more than a few more decades.  One critically endangered honeycreeper, the po'o-uli (Melamprosops phaeosoma), has a total population of three birds: two males and one female live in a reserve and the adjacent Haleakala National Park on Maui (BI 2000).  This small, masked brown-and-white bird, discovered in 1973 by a graduate student, once numbered 200 individuals before it underwent a drastic decline between 1975 and 1985 as a result of avian malaria and habitat destruction by feral pigs within its reserve (BI 2000).  All three birds live in separate home ranges, and the species has little chance of survival.
 
     Rails are the most characteristic of all island land birds.  These compact and stocky creatures are most frequently seen in wetland habitats, but some live in forests or grasslands.  Almost all islands in tropical latitudes have or had endemic rails or fossil evidence of their past presence.  Larger islands have several native rails, and it has been estimated that as many as 2,000 flightless rails inhabited Polynesian and western Pacific islands alone, prior
to their colonization or visits by humans who exterminated them.  Many of these instances were in prehistoric times by Maori, Hawaiians and other native peoples (Taylor 1998).  Some 23 species of island rails, virtually all flightless, have been exterminated since 1500 — far more than any other avian family (see Appendix). 
 
     Rails are not likely candidates for colonizing islands because they are, in the words of S. Dillon Ripley (1977), an authority on rails, "loath to fly."  When frightened, they usually do not take wing, but disappear into matted vegetation.  When they do fly for short distances, it is rather feebly, and their legs dangle down.  How could they have reached islands thousands of miles from the mainland?  Some rails are long-distance migrants, while other species disperse in erratic patterns (Taylor 1998).  Rails tend to travel in groups at night and are often blown off course.  European rails on their way to Africa have ended up far from their wintering site (Taylor 1998).  European Corncrakes, for example, have landed, exhausted, on ships in the Indian Ocean or even off New Zealand (Ripley 1977).  North American Purple Gallinules, colorful rails of southern marshes, have flown to tiny Tristan da Cunha island halfway between South America and Africa in the South Atlantic (Ripley 1977).  The Common Moorhen (Gallinula chloropus) of Eurasia, North and South America and Africa has colonized St. Helena, the Azores, the Seychelles, the Marianas and Hawaii, among other islands.  These colonizing rails usually become flightless if they have are no enemies, such as native predators. Some become the size of large chickens.  Once flightless, however, they are vulnerable to predation by animals brought by humans. 
 
     The Laysan rail or crake (Porzana palmeri) was driven to extinction by imported rabbits who rendered Laysan Island devegetated.  Biologists transported it to nearby Midway Island, where it flourished until World War II, when the island became a naval base.  The navy personnel were entranced by this utterly fearless and agile bird that sprung into people's laps or onto the mess table in search of crumbs of food.  Unfortunately, the species perished soon after 1942, when rats from a naval landing craft apparently ate the rail's eggs and preyed on its young.  A few of the rails had been returned to Laysan Island after rabbits were removed, but the vegetation had not recovered sufficiently and the birds did not survive (Ripley 1977).  Most other island rails have died out from similar causes.
 
     Since about one-third of the world's birds are endemic to islands, and they have been reduced by 30 to 50 percent since humans came to these islands.  Their extinctions represent a true biological catastrophe, in the words of Storrs Olson, an authority on extinct birds (Taylor 1998).  The vast majority of avian extinctions in the past 500 years have been island birds ‒ victims of predation, competition from introduced animals and disease from cagebirds.  Many were also killed for food or trade.  Non-indigenous species are still causing bird extinctions on islands.  In all, 137 of the 157 bird extinctions (87 percent) since 1500 have been island species, and human activities and animals introduced by humans have been responsible.  Island species have been more vulnerable to extinction than mainland species because of their small populations and limited habitats.  Many were flightless or slow-moving species, unable to flee predators, including humans.  Some were specialized in their diet and habitat and could not adapt to changes made in their environment. 


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