A Future for Birds
By Howard Youth
For millennia, birds have inspired people with their colors, songs, and behavior. Elegant and flashing pink, flamingos have long enjoyed such popularity. Their likenesses are featured in Iberian cave paintings dating back as far as 5,000 BCE, and ancient Egyptians used a flamingo silhouette as the hieroglyphic symbol for the color red. Today, flamingos and other birds also symbolize the dangers facing the planet's biodiversity.
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| American flamingos can be seen at the National Zoo. |
The Smithsonian National Zoo's flamingos belong to a salmon-pink subspecies called the American flamingo (Phoenicopterus ruber ruber). These water birds now breed in the wild in only four main colonies around the Gulf of Mexico. During the last century, disturbance, hunting, and habitat destruction forced them to abandon key breeding sites in Puerto Rico, Haiti, and Colombia. If the remaining breeding colonies face similar threats, these populations will likely plummet.
The flamingo is not the only bird in trouble. An increasing portion of the world’s almost 10,000 bird species, from the largest, the ostrich (Struthio camelus), to the smallest, the bee hummingbird (Mellisuga helenae), are suffering declines. Others are extinct or nearly so. The question is: Given the many threats facing feathered creatures, will the bird life of the future closely resemble that of today?
A 2000 book entitled Threatened Birds of the World, published by BirdLife International, reported that about 12 percent of the world's 9,800 bird species face extinction within the next century and that an additional eight percent may become threatened in the near future. Many widely distributed birds, such as ostriches, are undergoing region-wide declines. "People drive this extinction crisis," wrote the study's team of authors. "Of the 1,186 globally threatened birds, 1,175—99 percent—are at risk from human activities such as agriculture, logging, hunting, and trapping."
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Ostriches are suffering
declines. (Beth Jackson, USFWS) |
Conservationists mourn more than the loss of birds' beauty and songs. They worry that as bird populations decline, the critical natural services that those birds provide—dispersing seeds, pollinating flowers, controlling insect and rodent populations, and scavenging dead animals—will be eliminated. In Africa's tropical rainforests, for example, black-casqued, brown-cheeked, and piping hornbills (Ceratogymna atrata, C. cylindricus, and C. fistulator) are key seed distributors, eating various fruits, then scattering the seeds while feeding or defecating in different parts of the forests. In East Africa, a plains-dwelling species, the Von der Decken's hornbill (Tockus deckeni), works together with dwarf mongooses (Helogale undulata) on feeding and security teams. The mongooses wait for the hornbills to arrive, and then scare up prey while the birds sound he alarm if predators approach. If these hornbill species disappear, the health of these ecosystems could be disrupted.
Many birds are also considered indicators of environmental change—just their presence or absence can tell us something about the health of ecosystems. For instance, aquatic songbirds called dippers (family Cinclidae) frequent rolling streams that support their prey, caddisflies and other aquatic invertebrates. If streams become polluted or acidified—as they can if pine plantations supplant native deciduous forest—the prey, and consequently the dippers, often vanish.
Those Gone and Those Hanging
On
Since 1800, 103 bird species have gone extinct. Most
of these species—the dodo (Raphus cucullatus),
the Cuban macaw (Ara tricolor), and the Canary
Islands oystercatcher (Haematopus meadewaldoi),
to name a few—lived on islands, where introduced
species, over-hunting, and habitat loss quickly ravaged
native bird populations that evolved over millennia
in isolation. But not all the extinct species were castaways.
North America's passenger pigeon (Ectopistes migratorius)
was once one of the world's most abundant birds, until
it succumbed to widespread loss of its deciduous forest
habitat, market hunting, and Newcastle disease, a fatal
viral disease that was introduced to North America.
Habitat loss and degradation now present the single greatest overall threat to birds, including 85 percent of the most imperiled species. Like the passenger pigeon, however, many of these species face a deadly combination of human-wrought dangers. For example, a pheasant-sized New Guinean dove called the western-crowned, or blue-crowned pigeon (Goura cristata) disappears from forests near villages because of logging or clearing for farms, and because hunters shoot them for food and trappers illegally capture them for the wildlife trade.
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| A Malay great argus and her chicks at the National Zoo's Bird House. (Jessie Cohen/NZP) |
Many bird species can tolerate some logging or other extractive activities in their habitats, with varying success. The strident call of the great argus (Argusianus argus), a secretive forest pheasant with a flowing tail and cryptic plumage, can still be heard in lowland forests and even partially logged areas in Malaysia and Indonesia. Recently, however, the argus and another member of the pheasant family called the crested wood partridge (Rollulus rouloul) have vanished from many areas because their habitat has been altered so drastically that the birds do not have enough cover and food to survive.
Birds in more watery environs face a cocktail of threats. The wattled crane (Bugeranus carunculatus) of East Africa is one. This stately bird's breeding range spans thousands of miles from Ethiopia south to South Africa. The World Conservation Union classifies the wattled crane as vulnerable because, in the isolated wetland areas it occupies, water diversion projects, wetland destruction, poisoning, and other threats diminish the crane's breeding success. Collisions with power lines take a further toll on cranes and other large birds around the world, including bustards and storks.
Invasive Species, Guns, Cages,
and Longlines
Invasive species pose the second greatest threat to
the world’s bird diversity. Introduced rats, cats,
mongooses, and other invasive predators kill birds and
their young; non-native birds compete with native species;
and exotic pathogens knock out endemic birds that lack
disease resistance.
The brown tree snake (Boiga irregularis) represents a dramatic example of the destruction caused by introduced species. During the past 40 or 50 years, predation by non-native brown tree snakes caused the disappearance of all of Guam's endemic birds as well as its endemic reptiles. The flightless Guam rail (Gallirallus owstoni) was plucked from the brink of extinction when the last few individuals were removed from the wild and entered into a captive breeding program.
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| The brown tree snake is an invasive species that is threatening native bird species. (Gordon H. Rodda/USFWS) |
Brown tree snake populations on Guam still preclude the reintroduction of rails. But conservationists hope that someday Guam rails will again thrive on their native island, where short-term experiments with trapping, fencing, and other snake-control measures have had some success. Various zoos now breed Guam rails, and the National Zoo is the principal facility responsible for screening zoo-bred rails for diseases and other health problems before they are relocated to Guam. On nearby Rota Island, zoo-bred rails were introduced to a snake-free environment and have established a self-sustaining wild population. These intensive efforts may yet keep the Guam rail off the roster of extinct species, which already includes most of the Pacific islands' other endemic flightless rails.
Scientists fear that brown tree snakes may also populate Hawaii, where they have turned up at airports after hitchhiking on planes from Guam. Hawaii has lost 21 endemic bird species since 1500—about one-fifth of the world total of extinct bird species. Surviving endemic birds are threatened by introduced avian malaria and pox, invasive species, and habitat loss and degradation. One exception is a small greenish amakihi honeycreeper (Hemignathus virens). This hardy bird apparently can develop immunity to introduced diseases and live alongside non-native songbirds.
Other introduced pests may be small in size but can exact a huge toll on native birds and wildlife. The prolific yellow crazy ant (Anoplolepis gracilipes) has been marching across the Australian territory of Christmas Island since its introduction there in the 1930s. The ants now occupy 6,000 acres of rainforest, much of it in Christmas Island National Park, and they feed on bird chicks on the forest floor and all the way up to the forest canopy. Many scientists predict steep drops in the populations of Christmas Islands' endemic birds over the next decade as a result of the yellow crazy ant invasion. Scientists began dropping poison ant baits via helicopter onto the island's rugged forests in 2002 in an attempt to limit the introduced insects' colonies there. This effort proved successful, at least in the short term, knocking out all of the ants' super-colonies and reducing their population to low levels by 2003. Scientists continue to monitor and poison the ants.
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| Guam rails are nearly extinct on their native island. (Jessie Cohen/NZP) |
Invasive plants also alter habitats worldwide. In the Hawaiian Islands alone, plant communities are changing due to the incursion of roughly 900 species of exotic flowering plants. And in southern Florida, the Brazilian pepper (Schinus terebinthifolius) has overtaken hundreds of thousands of acres after its introduction as an ornamental plant. Unfortunately, native birds aid the spread of this South American plant: American robins (Turdus migratorius) and others eat the pepper's berries and scatter the seeds even in the most remote reaches of the Everglades.
Control of invasive species often requires costly and active management involving pesticides and other tools that could also harm native fauna. The United States spends as much as $137 billion a year to control invasives.
Introduced species aren’t the only culprits: Poorly regulated or illegal hunting and trapping "vacuums" birds from remaining habitats. In the Mediterranean island nation of Malta, for example, up to three million migratory birds are trapped or shot each year while migrating through the area. In Central and South America, palatable turkey-like birds called guans and curassows are among the first animals to disappear when hunters invade remaining pristine forest areas. The same holds true for 22 localized Asian pheasant species.
Parrots, while not widely hunted, are being loved to death instead. Almost a third of the world's 330 parrot species are threatened because they’re captured for the cagebird trade, and because their habitats are disappearing. Palm cockatoos (Probosciger aterrimus) of New Guinea and northeastern Australia are shot by subsistence hunters, and their lowland habitats are vanishing in New Guinea. Many are collected illegally for the bird trade. The National Zoo obtained its palm cockatoo pair when federal agents intercepted the two birds as they were being smuggled into the United States. The agents confiscated the cockatoos and turned them over to the Zoo.
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| Migratory birds such as robins eat the seeds of invasive plants and inadvertently spread them to new areas. |
The Bali mynah (Leucopsar rothschildi) is another species threatened by trapping. This gleaming white relative of the European starling hangs on in a single national park on the Indonesian island of Bali. Long in demand by bird collectors, who can fetch up to $2,000 for one bird, Bali mynahs are captured illegally. Only about a dozen individuals survive in the wild, but 1,000 live in zoos and collections around the world. In the future, these birds or their chicks may contribute to reintroduction efforts, just as National Zoo birds have in previous years. Corruption, poor park management, and theft of birds awaiting reintroduction in Bali have thus far stymied reintroduction efforts.
Another form of wildlife exploitation—longline fishing—inadvertently kills an estimated 300,000 or more birds each year. About a third of these are slow-breeding albatrosses that also suffer attacks on their nests from invasive rats and other predators. Albatrosses and petrels fly down to skim the water for floating bait, get hooked on longlines, and drown. Because longlines can stretch up to 80 miles, they can drown quite a few birds.
Few of the more than 30 nations with longline fleets have done much to reduce bird deaths, although mitigation measures—laying out nets at night, installing bird-scaring streamers, and putting weights on lines so that they sink faster—can dramatically reduce bird kills. Among the exceptions are Argentina, Australia, Ecuador, New Zealand, South Africa, and Spain. These six countries signed onto the Agreement on the Conservation of Albatrosses and Petrels, which went into effect in January. The ratifying countries agree to protect the birds' nesting grounds and reduce marine pollution, while fishing fleets working their waters must take steps to reduce bird bycatch in their longlines.
Tainted Homes
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| Bald eagle populations declined due to the use of the chemical pesticide DDT. |
As we invent, extract, and distribute chemicals around the world, the effects of particularly harmful substances come to light. Sometimes, birds provide us with the first signs of trouble. Chemical pollution affects birds in the oceans, near industrial sites, and in the countryside. Oil spills large and small kill many thousands of seabirds, including penguins, puffins, and gannets. The 1989 Exxon Valdez spill probably killed more than 250,000 birds in Alaska, while the 2002 Prestige oil spill off Spain's northwest coast was one of Europe's worst, claiming between 115,000 and 230,000 birds. Increased tanker traffic, aging vessels, and lax restrictions make the business of transporting oil even more hazardous.
The pesticide DDT caused North American bald eagle (Haliaeetus leucocephalus) and brown pelican (Pelecanus occidentalis) populations to crash after World War II until the chemical was banned in 1972. Scientists found that DDT built up in these birds, causing high mortality of their young through eggshell thinning and other complications. Since the United States banned DDT, many bald eagle and brown pelican populations have rebounded.
Pesticides kill or weaken millions of birds on farmland, and deplete their supplies of insect and wild plant food. Factories pump PCBs and other effluents into waters vital to both wildlife and humans. A study published in the journal The Auk in 2000 documented how immature tree swallows (Tachycineta bicolor) breeding in the PCB-contaminated Hudson River molt into adult coloration earlier, a sign that contaminants may be disrupting the birds' endocrine systems. In a 1999 study also published in The Auk, the same scientists, John P. McCarty and Anne L. Secord, described how tree swallows nesting at contaminated Hudson sites built smaller, poorer-quality nests than those constructed by tree swallows living elsewhere in New York state.
New chemical threats still surprise us. The steep, sudden decline of three Asian vulture species in India and Pakistan has baffled scientists over the last decade. Many supposed that a mysterious disease was wiping out the scavenging birds, which had been a common sight around areas where villagers disposed of cattle carcasses. In January, however, a study conducted by an international team of 13 scientists and described in the journal Nature concluded that the birds likely suffer from kidney failure after feeding on carcasses of animals treated with a widely used anti-inflammatory drug called diclofenac. The study's authors, who want the drug banned in hopes of reviving the vultures, call the die-offs the first clear case of major ecological damage caused by a pharmaceutical product.
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Birds sometimes
collide with man-made obstacles such as power
lines and skyscrapers. |
Solid constructions of glass and metal also pose problems for birds on the move. Millions of migrating birds die when they collide with skyscrapers, communications towers, and power lines. These threats, along with growing wind-farm networks, require careful study to determine safe locations and heights that will minimize bird collisions, although little work has been done in this area.
Unfortunately, global warming, which is caused by humans, must be added to the list of threats to bird diversity. Earlier bird breeding, migration arrivals, and some bird species' northward range expansions seem to indicate effects of global climate change. While some migratory species now arrive at their nesting grounds earlier than usual, others that adhere to traditional schedules seem to be at a disadvantage. Each spring, insect-eating pied flycatchers (Ficedula hypoleuca) migrate north from African wintering areas, arriving on Netherlands nesting grounds at around the same date. However, insect abundance is now peaking earlier, most likely in response to warmer climates, so the birds raise their young out of sync with peak food availability. Climate change will probably continue to alter bird habitats in coming decades, causing shifts in distribution and perhaps the demise of isolated species.
The Path Ahead
For a few hundred species, reintroduction programs are
salvaging birds from the brink of extinction. This is
happening to North America's largest waterfowl species,
the trumpeter swan (Cygnus buccinator), which
almost disappeared from the Lower 48 after at least
a century of over-hunting and habitat loss. Trumpeter
swan reintroduction efforts are now underway in Ontario,
Michigan, Ohio, Iowa, and other areas, and there are
plans to reintroduce them to East Coast states in the
near future. (In 2003, one of the National Zoo's trumpeters
was sent to Iowa for a 2004 release as part of that
state's reintroduction efforts.) Some critics worry
that the rebounding swan—a large, territorial
bird once inhabiting expansive habitats—could
stress isolated wetlands in the Midwest and East by
damaging vegetation and dominating food and nesting
sites now frequented by smaller bird species. Many waterfowl
aficionados, however, are thrilled to have the birds
back.
Decades of dedicated study lie ahead before we will fully understand bird ecology, distribution, and behavior. Unfortunately, across the globe, birds are running out of time. About one quarter of all bird species have ranges that are at most the size of West Virginia or Costa Rica. More than half of these species are threatened and declining, and for many, only fragmented habitats remain. They will be lost if we don’t protect them.
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| Trumpeter swans have benefited from reintroduction programs. |
In recent years, conservationists have been analyzing birds’ breeding and wintering areas and key migration stopovers, so they can determine which areas to protect as opportunities arise. More than 7,000 important bird areas (IBAs) in 140 countries have been catalogued so far. Also, hotspots for restricted-range and endemic species have been pinpointed in 218 endemic bird areas (EBAs), most of which lie in the tropics. BirdLife International spearheaded and coordinated efforts to catalog these areas. For example, "Java and Bali Forests" form one EBA, where the Bali myna is one of 34 restricted-range bird species. Some IBAs and EBAs already include designated reserves, but many others remain unprotected and poorly studied.
While reserve areas remain vital to protecting bird habitats, much of the world's land sits in private hands. Community, corporate, and government involvement in varied conservation efforts will be required to ratchet biodiversity and bird conservation to a higher status as part of a sustainable strategy for the planet. In a growing number of cases, enterprise and environmentalism are mutually beneficial.
Even flamingos are getting help from the corporate world. In February 2002, the Grand Bahama Power Company set up a 100-acre sanctuary next to its power plant, which electrifies the entire island of Grand Bahama. A nature center opened there and employees and community volunteers protect the wetlands on the site. Great efforts are taken not to disturb the sanctuary’s star attraction, nesting and feeding American flamingos. After all, these elegant pink waders are the Bahamian national bird, inspiring not only island visitors but also proud residents of a nation that hosts a once-declining but now stable flamingo population. As we work toward a more sustainable future, keeping an eye on flamingos and the world's other birds will help us keep ourselves in check—if we care to heed the warnings.
—Howard Youth, a ZooGoer contributing editor, has also written about bird decline in a paper entitled “Winged Messengers: The Decline of Birds” and in a chapter of the book State of the World 2003. Both were published by the Washington, D.C.-based Worldwatch Institute.
ZooGoer 33(3) 2004. Copyright
2004 Friends of the National Zoo.
All rights reserved.
