Klimaatverandering 43

De San Francisco Chronicle bericht: 'Where Are All the Birds? Startling New Figures on Rate of Extinctions Say 12% of Species to be in Peril by 2100.
by Jane Kay

The world's birds are disappearing in greater numbers than previously calculated, and the number of extinctions will grow even more dramatically by the end of the century, according to a grim study published today in the journal Proceedings of the National Academy of Sciences.
The study, the most thorough analysis of global bird species, says 12 percent of existing species -- about 1,250 -- are threatened with extinction by 2100.
Up until now, scientists had documented the extinction of about 130 bird species since the year 1500. But the study's authors -- from Stanford University, Duke University and the Missouri Botanical Garden in St. Louis -- say the more accurate estimate is about 500 extinctions out of more than 10,000 known bird species. That would be about one extinction per year over the last 500 years.
And that rate is 100 times higher than what was considered natural before human influence, the study said.
Over time, humans have cleared land for agriculture and other uses. They've hunted birds for food and sport. And they introduced other dangers, such as non-native birds, rats, snakes and diseases. Predictions of increased extinctions over the next century are based on these continuing threats as well as anticipated habitat loss linked to global warming.
Scientists say the decline of both the diversity and abundance of birds portends problems for the planet. Birds play a part in seed dispersal, plant pollination and insect control.
Critically endangered birds -- including the California condor and about 12 Hawaiian species -- are seen as most at risk of extinction.
The new study's extinction calculations include previously unknown bird species only discovered as fossilized remains as well as bird species missing for scores of years but never officially declared extinct. It also takes into account species wiped out by humans before modern scientific description began in the mid-1700s.
Local species may have disappeared without a trace, and the more fragile small bird species "may easily have gone extinct without leaving a record,'' the study says.' Lees verder:
http://www.commondreams.org/headlines06/0704-07.htm