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【Discussion】Six Australian birds declared extinct, although some could have be
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Six Australian birds that have not been seen in decades have been declared extinct by a team of scientists assessing the health of the country's bird species. In most cases they could have been saved, says team leader Stephen Garnett, professor of tropical knowledge at Charles Darwin University in Australia's Northern Territory. The lost birds include one species, the white-chested white-eye (Zosterops albogularis), along with five subspecies: the central Australian thick-billed grasswren (Amytornis textilis modestus), the Tiwi Island hooded robin (Melanodryas cucullata melvillensis), the southern star finch (Neochmia ruficauda ruficauda) as well as varieties of the spotted quail-thrush (Cinclosoma punctatum) and pied currawong (Strepera graculina ashbyi). Australia conducts a decadal review of its bird species. "We were worried about these birds when we last reviewed their status 10 years ago," Garnett said in a prepared statement. "Sadly, no sign of them has turned up in the past decade." According to the research team, the grasswren and currawong probably disappeared early in the 20th century. The white-eye and thrush were observed until the 1980s, and the robin and finch were last seen about 20 years ago. All six of these birds died off following the arrival of European settlers in Australia. Some made tasty meals for invasive rats. One fell victim to deforestation. Others disappeared after Aboriginal farming practices were abolished or replaced, Garnett tells Scientific American. "The white-chested white-eye probably succumbed to predation by black rats that arrived on Norfolk Island during the Second World War," Garnett says. Although poisoning invasive rats has helped save other species like the Norfolk Island green parrot (Cyanoramphus cookii), the practice was started too late to save the white-eye. The spotted quail-thrush used to live in a large eucalyptus forest near Adelaide, but Garnett says 90 percent of that forest has now been cut down. "The quail-thrush was highly fragmented in different patches and was last seen around the time of large bushfires in 1983," he says. The species could have been saved if the government and volunteers had stepped up to protect it as they did another rare species that was vulnerable to fires, the helmeted honeyeater (Lichenostomus melanops cassidix), he adds. Two of the species were lost following the introduction of cattle and sheep to the continent. The star finch required tall grasses near water, but its entire habitat "was subject to intense grazing by sheep and cattle for more than a century," Garnett notes. "In droughts the finch's habitat would have been grazed flat." He says fencing off a few sites, as is done for a similar subspecies in Cape York, would have saved the southern star finch. "Instead the last records were of birds turning up briefly in towns for a day or two then disappearing," he says. The thick-billed grasswren faced similar circumstances. Its habitats were "hammered by introduced rabbits and cattle, especially during drought," he says. Better management of cattle and earlier culling of rabbits, which are more controlled today, could have saved the wren. Changes in Aboriginal traditional practices led to the extinction of the hooded robin on Australia's Tiwi Islands. Aborigines used to periodically burn the brush on the island to reduce the likelihood of larger fires. According to the Northern Territory government, these activities "resulted in a mosaic of growth in terms of stages and types of vegetation development, which provided a range of food sources and habitats both for themselves and for the animals they hunted." But the arrival of Christian missionaries changed that. "When missions arrived on the Tiwis in the 19th century most Aboriginal people gathered there and the burning was largely abandoned," Garnett says. "These days government-funded Aboriginal ranger programs are reestablishing the fire mosaic, but too late for the robin." The plains of the Australian state of Victoria were also maintained by Aboriginal burning, "but the arrival of sheep and European settlers in the 1830s resulted in a collapse of the Aboriginal land management," Garnett adds. This resulted in isolated woodlands reconnecting to other woods as previously suppressed trees grew back for the first time since the last ice age. Previously isolated by distance, the pied currawong reconnected with another, more populous, subspecies and hybridized out of existence. These six birds will be listed as "presumed extinct" by the International Union for Conservation of Nature and Natural Resources's Red List of Threatened Species. Thirty bird species have now gone extinct in Australia in the past 100 years. |
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I even can not read it completely 8楼2011-01-14 20:27:40
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