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Stanford Report, January 10, 2005 	
Bird populations face steep decline in coming decades, study says



BY MARK SHWARTZ

Courtesy Cagan Sekercioglu/www.naturalphotos.com	
 Brown violet-ear
<http://news-service.stanford.edu/news/2005/january12/gifs/birds_brown_v
ioletear.jpg> 	
The brown violet-ear hummingbird is one of many species facing
extinction within the next century, according to a new study published
in the Proceedings of the National Academy of Sciences.	



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Ten percent of all bird species are likely to disappear by the year
2100, and another 15 percent could be on the brink of extinction,
according to a new study by Stanford biologists. This dramatic loss is
expected to have a negative impact on forest ecosystems and agriculture
worldwide and may even encourage the spread of human diseases, according
to the study published in the online edition of the Proceedings of the
National Academy of Sciences (PNAS) in December.

"Our projections indicate that by 2100 up to 14 percent of all bird
species may be extinct and that as many as one out of four may be
functionally extinct-that is, critically endangered or extinct in the
wild," said researcher Cagan H. Sekercioglu of the Center for
Conservation Biology (CCB) and lead author of the PNAS study. "Important
ecosystem processes, particularly decomposition, pollination and seed
dispersal, will likely decline as a result."

These findings come on the heels of the November 2004 Global Species
Assessment by the World Conservation Union (IUCN), which found that 12
percent of all bird species are already threatened with extinction,
along with nearly one-fourth of the world's mammals, one-third of the
amphibians and 42 percent of all turtles and tortoises.

"Even though only 1.3 percent of bird species have gone extinct since
1500, the global number of individual birds is estimated to have
experienced a 20 to 25 percent reduction during the same period," wrote
Sekercioglu and CCB co-authors Gretchen C. Daily and Paul R. Ehrlich.
"Given the momentum of climate change, widespread habitat loss and
increasing numbers of invasive species, avian declines and extinctions
are predicted to continue unabated in the near future."

Future scenarios 


The study was based on a painstaking analysis of all 9,787 living and
129 extinct bird species. Eight researchers spent a year collecting data
on the conservation, distribution, ecological function and life history
of every species-more than 600,000 computer entries in total. "The
result is one of the most comprehensive databases of a class of
organisms ever compiled," Sekercioglu said.

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 extinct or
on the brink of extinction by 2100. Birds with highly specialized diets
are predicted to experience more extinctions than average, they wrote,
adding that some plant species also face extinction if their primary
pollinators and seed-dispersers vanish.

"It's hard to imagine the disappearance of a bird species making much
difference to human well-being," said Daily, an associate professor
(research) in the Department of Biological Sciences and director of the
CCB Tropical Research Program. "Yet consider the case of the passenger
pigeon. Besides mail becoming a lot less fun to receive, its loss is
thought to have made Lyme disease the huge problem it is today. When
passenger pigeons were abundant-and they used to occur in unimaginably
large flocks of hundreds of millions of birds-the acorns on which they
specialized would have been too scarce to support large populations of
deer mice, the main reservoir of Lyme disease, that thrive on them
today."

Scavengers and insectivores 


More than a third of all scavengers and fish-eaters are
extinction-prone, according to the study, yet little is known about the
potential consequences of their widespread disappearance. "Since most
scavenging birds are highly specialized to rapidly dispose of the bodies
of large animals, these birds are important in the recycling of
nutrients, leading other scavengers to dead animals and limiting the
spread of diseases to human communities as a result of slowly
decomposing carcasses," the authors wrote.

As an example, the researchers pointed to India, where the collapse of
the vulture population in the 1990s was followed by an explosion of
rabid feral dogs and rats. In 1997 alone, more than 30,000 people died
of rabies in India, more than half of the world's total rabies deaths
that year.

The study also found that numerous insect-eating bird species face
extinction. "Exclusions of insectivorous birds from apple trees, coffee
shrubs, oak trees and other plants have resulted in significant
increases in insect pests and consequent plant damage," the authors
wrote, adding that the extreme specializations of many insectivorous
birds, especially in the tropics, make it unlikely that other organisms
will be able to replace the birds' crucial role in controlling pests.

"The societal importance of ecosystem services is often appreciated only
upon their loss," the authors wrote. "Disconcertingly, avian declines
may in fact portray a best-case scenario, since fish, amphibians,
reptiles and mammals are 1.7 to 2.5 times more threatened [than birds]."
Invertebrates, which may be even more ecologically significant than
animals, also are disappearing, they noted. Therefore, "investments in
understanding and preventing declines in populations of birds and other
organisms will pay off only while there is still time to act," the
authors concluded.

The PNAS study was supported by Dr. Walter Loewenstern and the Koret,
Winslow and Moore Family foundations.


*	


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L.A. Cicero	
 Cagan H. Sekercioglu
<http://news-service.stanford.edu/news/2005/january12/gifs/birds_cagan_v
ert.jpg> 	
Cagan H. Sekercioglu of the Center for Conservation Biology said that
"important ecosystem processes, particularly decomposition, pollination
and seed dispersal, will likely decline as a result" of the extinction
of bird species.	

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*	 Sekercioglu's faculty profile
<http://www.stanford.edu/%7ecagan/main.html> 	
*	 BirdLife International <http://www.birdlife.net/> 	
*	 IUCN  <http://www.redlist.org/> Red List of Threatened Species	

 
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