To forecast probable rates of extinction, he and his colleagues entered the data into a computer program designed to simulate best-case, intermediate-case and worst-case scenarios for the future.
The best case was based on the assumption that conservation measures in the next 100 years would be sufficient to prevent additional bird species from becoming threatened with extinction.
For the worst case, the researchers assumed that the number of threatened species will increase by about 1 percent per decade-that is, 1 percent in 2010, 2 percent in 2020, 3 percent in 2030, etc. "These assumptions are conservative, since it is estimated that, every year, natural habitats and dependent vertebrate populations decrease by an average of 1.1 percent," the authors wrote.
For the intermediate scenario, the scientists used statistics from 1994 through 2003 as a basis for calculating the likelihood that a non-threatened species would become threatened after a decade.
The results of the three future scenarios were dramatic. The computer forecast that between 6 and 14 percent of all bird species will be extinct by 2100, and that 700 to 2,500 species will be critically endangered or extinct in the wild. Even the middle-of-the-road intermediate scenario revealed that one in 10 species will disappear a century from now, and that approximately 1,200 species will be functionally extinct.
The study cited several reasons for the expected decline in bird populations, including habitat loss, disease, climate change, competition from introduced species and exploitation for food or the pet trade.
"Island birds are particularly at risk," the authors said, noting that one-third to one-half of all oceanic island species will be extin
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
13-Dec-2004