RESEARCHERS FIND EXTINCTION-THREATENED BIRD SPECIES IN UNEXPECTED PLACES

FAYETTEVILLE, Ark. - University of Arkansas researcher Tom Brooks and colleagues Lisa Manne and Stuart Pimm of the University of Tennessee have overturned a long-held belief that island bird species are more vulnerable to extinction than their continental counterparts.

The researchers reported their findings in this week’s issue of Nature.

Historically, a higher proportion of species extinctions have occurred on islands rather than on continents. So scientists have assumed that island species are inherently more vulnerable to the threat of extinction.

Manne, Brooks and Pimm studied the relationship between relative ranges and threatened species found the opposite to be true - lowland continental areas have a higher proportion of threatened bird species within similarly sized breeding ranges.

"Island species are actually less threatened for a given range size," Brooks said.

Manne, Brooks and Pimm examined the breeding ranges of nearly 2,300 song birds in North and South America - nearly one quarter of the world’s bird species. They compared the ranges of island, lowland and mountain bird species to see which areas contain the highest proportion of threatened birds.

A larger fraction of island species are classified as threatened - likely to become extinct in the medium-term future. However, for birds with middle-sized ranges, between 10,000 and 100,000 square kilometers, a higher proportion of lowland continental birds face possible extinction.

The scientists have two suggestions as to why the lowland species may be vulnerable, Brooks said. The first can be explained by bird ecology: Places with many birds, like the Amazon, tend to have fewer individuals of one species in a given range - making those species more vulnerable to habitat loss. On the other hand, in an ecosystem with fewer bird species, like the Andes, the birds tend to be more common throughout their range.

The other explanation is more ominous. In places where people have lived a long time, like the Caribbean, many bird species have already become extinct.

"Maybe people have already driven the threatened species to extinction," Brooks said.

After compiling their results, the researchers combined the information on lowland birds with the data on species that had ranges of 10,000 square kilometers or less - many of which are threatened - and created a map predicting where threatened species are likely to occur. They then compared the prediction map to a map of the threatened birds’ actual breeding ranges.

The scientists found areas in Brazil, Argentina and Paraguay which contain more threatened species than their model predicts. These areas indicate where extinctions will occur first, and should be the focus of immediate conservation measures, Brooks and his colleagues contend.

"If they don’t deal with these areas now, then their species are going to be gone," Brooks said.

Their research also points conservationists in another direction - protecting birds before they become endangered. The researchers suggest that areas containing many birds with small ranges, like some places in Costa Rica, Columbia, Ecuador and Peru, have potentially threatened populations.

The added and unexpected vulnerability of range-restricted lowland bird species gives conservation groups and governmental organizations another priority: To proactively protect these ecosystems now so bird species won’t disappear later, Brooks said.

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