Massive prehistoric bird extinction linked to human colonization

Research by Alison Boyer, a research assistant professor in ecology and evolutionary biology, and an international team studied the extinction rates of nonperching land birds in the Pacific Islands from 700 to 3,500 years ago. Some of the birds studied included birds of prey and ducks. The team uncovered the magnitude of the extinctions and insight into how and why human impacts varied across the region.

The findings are published in the current issue of the Proceedings of the National Academy of Sciences.

Scientists had long known extinction rates were high but estimates varied from 800 to 2,000 species due to an incomplete fossil record on the islands. The researchers used fossil records from 41 Pacific islands such as Hawaii and Fiji to run an analytical technique called the Bayesian mark-recapture method. This allowed them to model gaps in the fossil record for more than 300 Pacific islands and estimate the number of unknown extinct species.

"We used information on what species are currently on the islands and what species are in the fossil record to estimate the probability of finding a species in the fossil record," Boyer said.

Boyer and her colleagues found that nearly 983, or two-thirds, of land bird populations disappeared between the years of the first human arrival and European colonization. Disappearances are linked to overhunting by people, forest clearance and introduced species.

"We calculate that human colonization of remote Pacific islands caused the global extinction of close to a thousand species of nonperching land birds alone," said Boyer. "However, it is likely there are more species that were affected by human presence. Sea bird and perching bird extinctions will add to this total."

Researchers found the extinction rates differed depending on island and species characteristics. For example, larger islands had lower rates of extinction because they had larger populations of each bird species. Islands with more rainfall also had lower extinction rates because they experienced less deforestation by settlers. Bird species that were flightless and large-bodied had a higher rate of extinction because they were easier and more profitable to hunt and their lower rates of population growth inhibited recovery from overhunting or habitat loss.

"Flightless species were 33 times more likely to go extinct than those that could fly," said Boyer. "Also, species that only populated a single island were 24 more times likely to go extinct than widespread species."

Boyer collaborated with researchers from the University of Canberra in Australia, Institute of Zoology in London and King Saud University in Saudi Arabia.