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.
http://www.scientificamerican.com/blog/post.cfm?id=six-australian-birds-declared-extin-2011-01-06&WT.mc_id=SA_CAT_EVO_20110110
