|
Endangered Birds
Human activities have caused some 500 bird species worldwide to
go extinct over the past 500 years, and twenty-first-century extinction
rates likely will accelerate to approximately ten 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, says Stuart Pimm,
professor of conservation ecology at Duke's Nicholas School of
the Environment and Earth Sciences and one of the report's principal
authors.
Pimm's team, which pioneered the approach of estimating extinction
rates on a per-year basis, 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. The rate has speeded up in recent times. "Increasing
human impacts accelerated the rate of extinction in the twentieth
century over that in the nineteenth," the report said. "The
predominant cause of species loss is habitat destruction."
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.
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," says Peter Raven, president of the Missouri
Botanical Garden and co-principal author of the report. "One
can't register a bird as extinct if it was not known to exist in
the first place."
The report, which appears in the online edition of the Proceedings
of the National Academy of Sciences, is not all bleak, Pimm says. "The
good news in this report is that conservation efforts are reducing
extinction rates to about one bird species every three or four
years." But he adds that even this improved rate "is
still unacceptable."
Of the 9,775 known species of birds, "an estimated additional
twenty-five would have gone extinct during the past thirty years
if it were not for human intervention," Raven says. But, despite
conservation efforts, "some 1,200 more species are likely
to disappear during the twenty-first century. An equal number are
so rare that they will need special protection or likely will go
extinct, too."
www.pnas.org
|
