Researchers said the findings are a wake-up call pointing to the need for new strategies to ensure that protected lands and the ranges of threatened species overlap.
At present, the largest protected areas are in desert or cold climates where the biodiversity is far lower than in tropical areas teeming with life, said Stuart L. Pimm, a professor of ecology at Duke University.
"The protected areas tend to be in the wrong places. We have huge national parks in Alaska, but few protected areas in biologically rich places like Florida or Hawaii," said Pimm, who was not involved in the research.
The findings appear in Thursday's issue of the journal Nature.
In the study, researchers from nine nations compared maps of more than 100,000 protected areas around the globe to maps of the ranges of 11,633 animal species - mostly tropical and many threatened or endangered.
They found that for about 12 percent of the species, their ranges did not include parks or nature preserves that would protect them from human activities such as logging, hunting or mining operations.
And among 3,896 species deemed threatened, they found that 20 percent had no protection. About 300 of those animals are on the verge of extinction.
They include a tiny Colombian marsupial called Handley's slender mouse opossum and Indonesia's Cerulean Paradise-flycatcher, a bright blue bird with 100 or so survivors confined to a single forest-topped extinct volcano. Other critically endangered species are the Comoro black flying fox, a fruit bat found only on the Indian Ocean's Comoros islands, and Myanmar's Burmese star tortoise.
Smaller studies have shown "gaps" between protected areas and threatened species, but the new work offers the first global view of that situation by evaluating the predicament of some of the best documented animal species, said Ana S.L. Rodrigues, a research fellow at Conservation International in Washington, D.C.
"Even for these species that we know well, we're finding these levels of unprotection, of gaps. It's alarming," said Rodrigues who was the study's lead author.
Although about 11.5 percent of Earth's land surface has protected status, she said many developing nations simply lack the resources to protect their national parks. Conflicts over conservation are common, she said, because areas highly attractive to humans such as fertile lowlands and forests are also the richest in species.
Craig Hilton-Taylor, a Cambridge, England-based conservation biologist with the World Conservation Union, called the research "scary" because it did not even look at thousands of little-known species such as small mammals, freshwater fish, plants and invertebrates that have very tiny ranges.
"We have a long way to go before we can say, 'Yes, we are truly conserving the world's biodiversity,"' he said.
By Rick Callahan