Early hunters are guilty as charged. (Paleontology).

The spread of humanity around the world often coincided with extinctions of large animals. For example, when humans migrated to the Americas--traditionally dated to 11,000 years ago--around 135 mammalian species disappeared within a few hundred years. Similar extinctions occurred in Australia and on Pacific islands (SN: 12/4/99, p. 360). In New Zealand, roughly 40 bird species vanished within 5 centuries after the Maori arrived in the early 130Os.

Some scientists deny that people are to blame for these sorts of extinctions, pointing instead to such factors as climate change, says Trevor H. Worthy of Paleofaunal Surveys in Masterton, New Zealand. Even for those species clearly decimated by humans, he says, it's hard to determine whether hunting, habitat destruction, or the introduction of pests such as rats contributed most to the demise.

To address this uncertainty, Worthy and his colleagues examined bird remains at Marfells Beach in New Zealand. The area contains skeletons that accumulated without human intervention over the past 1,800 years and the bones of birds that were hunted by the early Maori.

The researchers reasoned that if an over-abundance of bones from a given bird species shows up at a Maori site, compared with a wild habitat in the area, that would indicate that the Maori's favored the species for hunting.

In the March 7 Proceedings of the Royal Society of London B, Worthy and his colleagues report finding such patterns for some species. Many more of these preferentially hunted birds went extinct than did species not on the Maori menu. All birds, however, were exposed to habitat destruction and invasive pests.

"Our data show clearly that the animals that went extinct ... were preferentially hunted," says Worthy.

"It would be difficult to refute this extremely persuasive study," says John Alroy of the University of California, Santa Barbara. Understanding historical cases of human-mediated extinction puts people's current ability to threaten species in perspective, he adds. --J.P.