Prehistoric Bird Extinction Linked to Human Colonization

Research from the University of Tennessee, Knoxville shows that about a thousand bird species likely became extinct due to human colonization.

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

As scientists suspected high extinction rates, 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 Bayesian mark-recapturing, an analytical technique used to model gaps in the fossil record for more than 300 Pacific islands. It also allowed them to 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 over hunting 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 non perching 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."

Extinction rates differed greatly depending on the island and characteristics of certain bird species. 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. Many species may have been more profitable to hunt, including birds that were flightless and large-bodied.

"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."

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