Late-Holocene Bird Extinction Linked to Human Colonization

A new research published in the Proceedings of the National Academy of Sciences suggests that more than 1,000 bird species became extinct on Pacific islands following human colonization.

Restoration of the Lesser Megalapteryx, also known as the Upland moa, Megalapteryx didinus. The Lesser Megalapteryx was the last moa species to become extinct (Lionel Walter Rothschild)

Restoration of the Lesser Megalapteryx, also known as the Upland moa, Megalapteryx didinus. The Lesser Megalapteryx was the last moa species to become extinct (Lionel Walter Rothschild)

Scientists had long known extinction rates in the region were high but estimates varied from 800 to 2,000 bird species.

The researchers led by Prof Tim Blackburn of the University of Tennessee studied the extinction rates of nonperching land birds on Pacific islands from 700 to 3,500 years ago. They 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,” said co-author Prof Alison Boyer, also from the University of Tennessee.

The team 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,” Prof Boyer said. “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.”

Species lost include several species of moa-nalos, large flightless waterfowl from Hawai’i, and the New Caledonian Sylviornis, a relative of the game birds but which weighed in at around 30 kg, three times as heavy as a swan.

The 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,” Prof Boyer explained. “Also, species that only populated a single island were 24 more times likely to go extinct than widespread species.”

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Bibliographic information: Richard P. Duncan et al. Magnitude and variation of prehistoric bird extinctions in the Pacific. PNAS, published online before print March 25, 2013; doi: 10.1073/pnas.1216511110