Thanks to all of you who answered and provided information. Let me
summarize what I have learned.

The 1000 extinctions since 1000 AD figure comes from estimates that bird
extinction rates have been ca 1/yr. The best reference for these data is
an article by Pimm et al, Proc. National Academy of Sciences 103, 10941,
2006.

The list of bird extinctions since 1500 now totals 154 (ca 0.3/year).
Most of these are from islands, where extinctions have been much more
severe. Many additional extinct birds are being described from fossils,
but dating them to the past 1000 years is unlikely for most. In the past
century there have been 53 extinctions (0.53/year).

Pimm et al argue that the 1500-2000 era extinction rate of 0.3 birds/year
is an underestimate, based largely on the fact that no bird species were
"recognized" prior to the late 1700s, and that many species have only been
described in the past 100 years. I think they are arguing that many
undescribed species will have become extinct between 1500 and the time
they might have been described (1800-1900). I find these arguments
unconvincing.

Of course scientists keep producing new species, and also removing other
species. Those certainly don't count in the extinction numbers.

************************
Robert Cleland

Professor (Emeritus), Biology Dept. Box 355325
Univ. of Washington
Seattle, WA 98195-5325
Phone (206) 543-6105; FAX (206) 685-1728