POSTED 19 MAY 2005
Extinction: Birds do it...
As the reappearance of the ivory-billed woodpecker shows, it's seldom
clear exactly when a species actually goes extinct, even when its habitat
has been largely destroyed. One dramatic example of an organism that has
unexpectedly returned is the cahow, or Bermuda petrel, a carnivorous seabird
that was not seen for 300 years (although it's not clear that many people
were searching for it). 
The
bird was too tasty -- or too tame -- for its own good, says author Scott
Weidensaul. "When it was discovered in the early 1500s, it was incredibly
tame, a common seabird, and the English colonists discovered it and ate
it out of existence." By 1621, the bird was considered extinct, and only
in 1951 were 18 nesting pairs discovered on isolated island in Bermuda.
The dodo bird was native to Mauritius, an island in the Indian Ocean. It was discovered in 1598 and "dead as a dodo" by 1681. Dodo and Red Parakeet, painting by William Hodges, National Library of Australia
By 1992, an estimated 150 cahows were living on islets with a total area of 1 hectare, and the Lazarus-like cahow could be extinguished for real as global warming continues to raise sea level.
If you want the big picture of species extinctions, you go to NatureServe, a clearinghouse of species information in the Western Hemisphere. The group places possibly-extinct species in one of two categories:
GX (Global presumed extinct) "Not located despite intensive searches and virtually no likelihood of rediscovery."
The NatureServe categories are not identical to our usage: In common language, "presumed extinct" is GH -- there is some hope for finding the species again. No matter; we'll use the letters instead. Bruce Stein, vice-president for programs at NatureServe, told us that the intensity of searching done is a key factor in determining GH or GX status. He says that NatureServe puts a species in GX only "if exhaustive searches of all suitable habitat have been carried out and there is no more cause for hope."
Stein was a coeditor of Precious Heritage, the Status of Biodiversity in the United States. He says the book, published in 2000, listed 100 U.S. species (40 vertebrates, 49 invertebrates, and 11 plants) as GX. Another 439 U.S. species, including the ivory-billed woodpecker, were deemed GH.
Purple milkweed, Asclepias purpurascens, is a prairie plant that
may appear spontaneously in prairie restorations, says Mark Leach of the
University of Wisconsin-Madison Arboretum. Just as species can go extinct,
so can landscapes: in the Midwest, prairies and oak savannas nearly vanished
due to population pressure, agriculture and development. Photo by Raphael Carter, Chapparaltree.com
Is the absence of evidence evidence of absence?
A species must be near the end of its rope to be considered GH (possibly
extinct). But that listing can be a benefit, since it challenges field
biologists to search for the dear departed species. Stein says that when
NatureServe funded researchers to look for 104 GH species, 16 were rediscovered.
Dean Taylor, a research associate at the Jepsen Herbarium at the University of California at Berkeley, is one botanist who has searched for presumed-extinct plants. California's plants, Taylor told us via email, are "unique amongst temperate floras of the Northern Hemisphere in that nearly half of the 7,000 native plants are found nowhere else but in California."
In
the early 1970's, Taylor says, California botanists began listing the
state's rare or endangered plants, and the California Native Plant Society
later named 84 plants as presumed extinct in the state. Several of them
were rediscovered, Taylor says, so "It was clear that placing them in
the 'presumed extinct' [category] was highly premature."
The shasta owl's clover was once presumed extinct. In 1996, a few were found in part of California's Shasta Valley, but the landowner has forbidden botanists to visit the imperiled plant. These plants are parasites that derive most nutrition from the roots of other plants. Photo: Courtesy Dean Taylor.
Among the rediscovered plants was shasta owl's clover, which, Taylor tell us, "was discovered in 1876 by a very prolific botanist, E.L. Greene, who at the time was preaching at his church ... and later became the first professor of botany at the new University of California in Berkeley."
In 1996, with the plant presumed extinct, Taylor found a few in a "very small and diverse remnant of native prairie in Siskiyou County," in far northern California. No plants were seen in 1997, but they reappeared in 1998. And then -- a question mark. "After 1998, the landowner would no longer permit botanists to visit the site, and I am under the understanding that the site has not been revisited since then," Taylor wrote us.
Until 1996, shasta owl's clover (Orthocarpus
pachystachus) was presumed extinct in California. A few plants have
been discovered in northern California. Courtesy
Dean Taylor.
Why bother?
What is the attraction of searching for life forms that others have failed
to find? For one thing, you get respect from academic colleagues for reanalyzing
old records, finding a "lost" species, and publishing your results. But
even more basic is the need to know: Searching for rare species, whether
you find them or not, helps biologists make sense of the realm of life.
Species, after all, are the building block of life itself, and in recent years, the rate of species extinctions has accelerated. The International Union for the Conservation of Nature estimates that species are going extinct at 1,000 to 10,000 times the normal rate.
Weidensaul, who has written about, and participated in, rediscovery quests, says they carry this "whole notion of hope. These are fairly grim times for conservation, We are in the midst of the sixth mass extinction, and this time we can't blame it on a meteorite or an asteroid; there are so many people taking up so much space. The thought that every once in while we get a second chance is pretty heady stuff. By no means does it balance out the loss of thousands of species every year, but it gives us hope."
Lessons learned?
The
rediscovery of the woodpecker does not prove that extinction has been
overhyped. But what does it prove?
First, that listing species as presumed extinct does encourage biologists and ordinary people to go to unreasonable lengths to find them.
Colorized photo: copyright © George M. Sutton/Cornell Lab of Ornithology, from Big Woods Conservation Partnership
Second, our knowledge of the life around us is riddled with gaps. "The largest American woodpecker was able to successfully elude our notice for 60 years," says Stein, "and it wasn't for lack of looking. That shows how much we have to learn."
Third, preserving or restoring native habitat can help many imperiled species. "The big lesson is that it really is all about the habitat," Stein says. "As long as there are some large chunks of habitat left, it is surprising how resilient nature can sometimes be."
Finally, a few miraculous resurrections will not reverse the growing trend of death and extinction for the rare, beautiful, and highly adapted forms of life on Earth.
Find your rebirth in our bibliography.
