Debate Over Bird Extinction Risk

Data from the Atlantic forests show that, although 90 percent of the area has been cleared, no bird species has yet become extinct.

However, Andrew Balmford of Department of Animal and Plant Sciences at Britain's Sheffield University and Thomas Brooks of the Department of Ecology and Evolutionary Biology at the University of Tennessee say the theory is valid pointing out that there is a "time lag" between deforestation and extinction.

Publishing their conclusions in a March 14 issue of the leading British science journal Nature, they say many species are now in "serious danger of extinction" unless immediate conservation action is taken.

They looked at predictions for species extinctions in the Brazilian Atlantic forest and compared them with current bird counts using data from BirdLife International, an international federation of NGOs dedicated to preventing the extinction of birds.

When threatened species were compared with theoretical predictions the correlation was very close. Using this approach they predicted 88 extinctions of endemic species out of a total of 214 with a further 60 species under threat.

"Without immediate conservation action, the numerous Atlantic forest birds currently threatened will soon become extinct," they warn.

This approach, which predicts that the loss of 90 percent of an area will lead to the extinction of half its species, is now under attack. The most ardent criticism came in a recent book, "Nature's Keepers" by Stephen Budiansky, who says predictions based on the species/area relationship are a "biological absurdity."

However Balmford points out that predictions are not meant to be instantaneous. "We are not predicting extinction tomorrow but gradually over time," he says.

"That is why we decided to test the model by looking at threatened endemic species using data collected independently."

He adds that using the same method there is evidence that the theory can also be applied with good match to forests in the Philippines, Indonesia, other far east areas and the northern United States.

He notes that generally deforestation rates are increasing, "But even worse, we found that those areas losing forests at a higher rate have the largest number of endemic species."

Adrian Long of BirdLife International explains that some areas are far more important for preserving biodiversity than others.

"These include the Atlantic coastline forests of Brazil which are incredibly important," he says. "It is not just the number of species which is important but the number which is unique to the area.

"The Atlantic forests have the highest concentration of unique species anywhere in the world. This means we are not just looking at potential local extinction but global extinction for the species under threat."

However deforestation and development in general is destroying many natural habitats and several species are already extinct including the Colombian Grebe, Glaucous Macaw and Slender-billed Grackle.

BirdLife calculates that 290 species, or 8 percent, of the region's birds are now threatened with extinction. BirdLife has identified 596 "key areas" -- the most important areas within the region for these threatened species where conservation measures could be cost effective.

However only half of these are subject to protective measures at present and in many cases these are not properly implemented.

In this context, Andrew Balmford believes validating the species/area theory is important. "Much of the political impetus for conservation comes from raising public concern using figures. It is very important for the figures to be right. It is important to show that we are not 'crying wolf'."