http://www.eurekalert.org/pub_releases/2006-07/du-bge070506.php
Birds going extinct faster due to human activities
Public release date: 5-Jul-2006
DURHAM, N.C. -- Human activities have caused some 500 bird species
worldwide to go extinct over the past five centuries, and 21st-century
extinction rates likely will accelerate to approximately 10 additional
species per year unless societies take action to reverse the trend,
according to a new report.
Without the influence of humans, the expected extinction rate for birds
would be roughly one species per century, according to Stuart Pimm,
professor of conservation ecology at Duke University's Nicholas School
of the Environment and Earth Sciences, who is one of the report's
principal authors.
"What our study does, for the first time, is provide a well-justified
and careful estimate of how much faster bird species are going extinct
now than they did before humans began altering their environments,"
said Pimm, whose research group pioneered the approach of estimating
extinction rates on a per-year basis.
"Extinction rates for birds are hugely important, because people really
care about birds," he said. "People enjoy them, and bird watching is a
big industry. So we know the rates of bird extinctions better than the
rates for other groups of species."
"Habitat destruction, selective hunting, invasive alien species and
global warming are all affecting natural populations of plants and
animals adversely," added Peter Raven, president of the Missouri
Botanical Garden, who is co-principal author of the report and a
longtime collaborator with Pimm.
The report will appear in the online edition of the Proceedings of the
National Academy of Sciences during the week of July 3-7, 2006. Other
authors are Alan Peterson, a physician in Walla Walla, Wash., and Paul
Ehrlich and Cagan Sekercioglu, conservation biologists at Stanford
University.
The researchers calculated that since 1500 -- the beginning of the
major period when Europeans began exploring and colonizing large areas
of the globe -- birds have been going extinct at a rate of about one
species per year, or 100 times faster than the natural rate.
And the rate has been faster in recent times. "Increasing human impacts
accelerated the rate of extinction in the 20th century over that in the
19th," the report said. "The predominant cause of species loss is
habitat destruction."
These findings do not mean Europeans have caused all of the extinctions
of birds over the course of time, the researchers said. "Europe's
exploration of the rest of the world merely continued to extinguish
species at rates similar to those caused by the earlier Polynesian
expansion across the Pacific," they said in the report.
The new assessment considerably exceeds previous scientific estimates
that 154 bird types disappeared during that past 500 years, according
to the researchers.
One factor contributing to such large differences in estimates is that
"more than half of the known species of birds were not discovered until
after 1850, an important point that previous estimates of extinction
rates have failed to take into account," Raven said. "One can't
register a bird as extinct if it was not known to exist in the first
place."
According to Pimm, as recently as 1815 scientists were aware of only
about 5 percent of the world's birds. "The reality is that scientists
did not know about most remaining bird species until about 1845 or
1850," he said.
The new report is not all bleak, Pimm said. "The good news in this
report is that conservation efforts are reducing extinction rates to
about one bird species every three or four years," he said, but he
added that even this improved rate "is still unacceptable."
Of the 9,775 known species of birds, "an estimated additional 25 would
have gone extinct during the past 30 years if it were not for human
intervention," Raven said.
Despite conservation efforts, "some 1,200 more species are likely to
disappear during the 21st century," he warned. "An equal number are so
rare that they will need special protection or likely will go extinct,
too."
The forecast may be even bleaker for other types of animals, the
researchers said.
"We do not give the kind of special attention to other groups of
organisms that we do to birds, and extinction rates for them are likely
to be much higher over the 21st century and beyond," Raven said.
The researchers derived their estimates using a large database of
threatened and endangered species compiled by Bird Life International
in Cambridge, England. They also used a compilation by report co-author
Alan Peterson of the first scientific descriptions of bird species.
"Knowing when species were first described to science turned out to be
a hugely important part of this story," Pimm said.
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