His gloomy prediction proved accurate. By the mid 19th century the great bustard was extinct in Britain. In the rest of Europe its distribution is greatly diminished.
The disappearance of native birds is often heralded by the arrival of alien animals, says Youth.
The dangers of such introductionsboth deliberate and accidentalare evident on remote islands. Having evolved over hundreds of thousands of years to suit the conditions of their isolated homes, many island birds are ill-equipped to cope with outsider competitors or predators.
For instance, Hawaii's endemic bird species are being put to flight by a variety of invaders, including cats, rats, feral pigs, and mongoose.
On St. Lucia, the small Indian mongoose was brought in to deal with an earlier influx of rats. Unfortunately, the mongoose also developed a taste for the white-breasted thrasherone of the Caribbean's most endangered birds.
The mammal was also introduced to control rats on Mauritius in the Indian Oceanonce home to the famous dodo. This strange, flightless pigeon epitomized the problems faced by endemic island species. Waddling was no defense against hungry sailors.
Meat-eating, acid-spitting yellow crazy ants have imperiled the Christmas Island hawk-owl and Abbot's booby. The birds are found only on Christmas Island. The Australian government has been scattering poisoned bait from helicopters to keep the ants at bay.
Introduced birds can be just as dangerous. A massive cull of ruddy ducks is about to begin in Europe in an effort to save Spain's white-headed duck.
The ruddy duck, a native of North America, is now interbreeding with its close relative. Conservationists say the white-headed duck will soon be wiped out if drastic action isn't taken to stop the sexually precocious invader.
"The tragedy of this situation is that the ducks themselves are not to blame," said a spokesman for the Royal Society for the Protection of Birds in Britain. "They are doing what comes naturally to them, having been placed in an unnatural situation by the actions of humans."
Youth says similar actions mean many other birds are living on the brink. He says more than 20 localized pheasant species in Asia are endangered by over-hunting. And almost a third of the world's 330 parrots are facing extinction following habitat loss and trapping for the pet trade.
Conservationists say unregulated fisheries in the southern oceans are endangering the albatross. Thousands of birds are being hooked and drowned on baited longlines set for fish.
Richard Thomas, communications manager for BirdLife International, said: "Of the 21 albatross species recognized by BirdLife [some say 24 species], 17 are currently considered at risk of global extinction due to longline fisheries."
Global warmingwidely regarded as a manmade phenomenonalso looks set to become a key factor in determining the plight of many species.
In Britain, for instance, temperatures are estimated to rise by as much as 2.6 degrees Celsius (4.7 degrees Fahrenheit) in the next 50 years. If they do, the capercailliethe world's largest grouseis predicted to lose 99 percent of its pine forest habitat.
In North America, the Arctic tundra is expected to retreat northwards and be replaced by forest. The globally threatened spoon-billed sandpiper could lose 60 percent of its nesting sites.
Youth says conservation efforts must take account of man's impact on the wider environment, instead of focusing on isolated wildlife reserves. Isolation means vulnerabilityas the dodo's story proves.
Youth concludes: "Birds provide us with food, inspiration, a link to nature, and an alert system for detecting environmental ills, but today, this feathered resource is in great need of attention."
More Bird Stories by National Geographic News:
Tall As a Deer, Huge U.K. Bird Staging a Comeback
Memory Aids Birds in Migration, Study Finds
Crows Better at Tool Building Than Chimps, Study Says
Extinction Near for Albatross, Experts Warn
51-Year-Old Albatross Breaks N. American Age Record
Are Flashy Male Birds Threats to Their Own Species?
Wild and Escaped Parakeets Captivating City Dwellers
Bright Beaks Signal Health to Female Birds, Study Says
Coot Birds Can Count, Study Says
Falconry Used to Secure North American Airports
Cuckoos, Wrens in Escalating Evolutionary Arms Race
Deer Behind Britain's Great Bird Decline?
"Mysterious Plague" Spurs India Vulture Die-Off
Gamblers Fuel Trade in "Lucky" Vulture Heads in Africa
Ospreys Flock to Cuba, With Conservationists Close By
Recent "Birder's Journal" Stories from Robert Winkler:
Giving Thanks for Wild Turkey Sightings
Birder's Journal: Ghost Town's Curse Haunts New England Forest
Birder's Journal: Looking at a Handy New Guide
Birder's Journal: Learning to Let Birds Come to You
Birder's Journal: A Morning With Migrants
Birder's Journal: This Warbler Is a Master of Deception
Birder's Journal: Seduced by Dueling Thrushes
Birder's Journal: Attack of the Flying Goshawk
Nationalgeographic.com Bird-Watching Sites:
Florida Keys Area
Maine's Acadia National Park
New Orleans Area
New York City Area
North Carolina's Outer Banks
Rocky Mountain National Park
Salt Lake City Area
San Francisco Area
Santa Fe Area
South Dakota's Black Hills
Washington's Olympic National Park
Wyoming's Grand Teton National Park
Yellowstone National Park
Yosemite National Park
Additional Information from Related Web Sites:
American Bird Center
American Bird Conservancy
Fish and Wildlife Service Bird Web Site
National Audubon Society
Environmental Protection Agency: Bird Conservation
SOURCES AND RELATED WEB SITES