Scientists Must Be Thorough While Measuring Extinction
The United Nations said recently that man-made threats such as rising populations, felling of forests, hunting, pollution and climate change are all contributing to the world’s worst spate of extinctions since the dinosaurs vanished 65 million years ago.
Yet scientists must undergo endless searching to prove that any individual species has gone the way of the dodo.
"If there’s one thing in my career I’d like to be proved wrong about, it’s the baiji," said Sam Turvey of the Zoological Society of London, using another name for the Yangtze River dolphin.
Turvey interviewed Chinese fishermen for almost 3 months earlier this year, hoping to record sightings of the long-snouted dolphin, which has not been seen since 2002. Some colleagues in China are still looking.
In 2006, the baiji was almost declared extinct after an acoustic and visual survey of the river turned up nothing. Yet a blurry video forced experts to rate it "possibly extinct."
According to the International Union for Conservation of Nature’s (IUCN) Red List, about 300 plant and animal species, including the Christmas Island shrew and the Venezuelan skunk frog are also "possibly extinct," the worst category short of extinction.
Mike Hoffmann, who manages a global project to assess species for the IUCN and Conservation International, said if Turvey’s study turns up no firm evidence, it would likely push the Yangtze River dolphin into the "extinct" column.
The Yangtze River Dolphin would be the first "megafauna" mammal — one weighing more than 100 kg (220 lb) — to die out since the Caribbean monk seal in the 1950s.
"To say something is extinct requires quite a lot of proof, of negative evidence, and may take many years to collect," said Craig Hilton-Taylor, the manager of Red List.
Scientists on the "possibly extinct" assignments must search through the undergrowth for rare plants, frogs or rats, set up night-time traps for bats or moths, or scour the seabed for corals.
Since 1985, no one has seen the Christmas Island shrew in its Australian habitat. The Venezuelan skunk frog, known from a cloud forest habitat of 10 sq km (3.9 sq mile), has yet to be found despite numerous searches.
Still, scientists say species are disappearing at a rate faster than ever.
Since 1500, some 76 mammals have gone extinct, a much faster rate than in previous centuries, and 29 are "possibly extinct" on the 2008 Red List.
Unknown economic value may exist in some extinct species, such as the Australian gastric brooding frog, which incubated its young in its stomach and might have pointed to ways to treat ulcers. South Africa’s bluebuck antelope could have even boosted tourism.
Still, some species often thought to be extinct end up making surprising appearances. Last year, a lizard presumed extinct turned up on La Palma in Spain’s Canary Islands after no sightings in 500 years.
Australian scientists were even delighted to find two dead night parrots in 2006 and 1990, suggesting the reclusive species continues to survive.
The majestic green sphinx moth, known from one Hawaiian island, was written off as extinct but experts on another island were shocked to catch one in a net.
But Hoffmann said Red List’s demands for evidence meant that it probably underestimated the pace of extinctions. Searches have to be rigorous, at the right seasons, and in nearby habitats, with the correct equipment.
“Scientists want to be cautious because of the finality of extinction”, he said.
The confusing “possibly extinct” category is so bleak that it does not even include the critically endangered ivory-billed woodpecker — subject of speculation about a U.S. comeback after reported sightings in Arkansas in 2004.
Hilton-Taylor said it has never been listed as ‘possibly extinct’ because there were sightings 20 to 30 years ago in Cuba. "There is still good habitat there."
Declaring a species extinct means it inevitably ends cash for conservation — lending agencies such as the Global Environment Facility use Red List data.
When one species goes extinct, new ones become endangered, such as on the Yangtze River, where the finless porpoise and the Chinese paddlefish, reported to grow up to 7 meters (23 feet), are also in danger.
Turvey said the problem with the Yangtze is that the threats are still there and they are escalating.
And larger threats remain. In 2007, the U.N. Climate Panel said that up to 30 percent of species face increasing risks of extinction if temperatures rise by another 1 degree Celsius (1.8 Fahrenheit).
The panel, which says temperatures rose 0.7 C in the 20th century, also forecasts more droughts, heatwaves and rising seas linked to human emissions of greenhouse gases spurred mainly by burning fossil fuels.
Birdlife expert Stuart Butchart wrote in a 2006 report that 150 bird species had gone extinct since 1500, or 0.3 a year. That was 30-300 times the background rate of extinctions — a natural process deduced from fossil records.
The exact number of species on earth is unknown; yet one U.N.-backed study estimated 5-30 million against about 2 million documented so far.
The U.N. Convention on Biological Diversity estimates they may be vanishing faster than they are found, at a rate of three per hour, the fastest in millions of years.
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