August 5, 2012
Birds In New Zealand Face Extinction
redOrbit Staff & Wire Reports - Your Universe Online
Keys to survival today differ from those of the past. This is revealed in a new study of nearly 300 species of New Zealand birds – from pre-human times to the present.
Lead author Lindell Bromham of Australian National University said, "Taking into consideration the growing number of studies that try to predict which species could be lost in the future based on what kinds of species are considered most threatened today the outcome is important."
More than one out of four of New Zealand's native bird species have become extinct in the roughly 700 years since humans arrived in the remote islands that make up New Zealand.
"Many species were hunted to extinction. Others were eaten by the animals humans brought with them – such as cats, rats and weasels – or pushed off their land as humans cleared and burned forests to make way for farms and pastures," according to the study.
Researchers examined whether biological qualities such as body size might help scientists determine which species were likely to perish, and whether those risk factors held up over time.
They analyzed extinction patterns for New Zealand's native birds across four time periods in New Zealand's history, from pre-human times to the present to find out. Included in the data was 274 species of living and extinct birds, such as penguins, geese, ducks gulls, pigeons, parakeets and wrens.
Biological traits that best predicted extinction risk in each time period were looked at by the researchers. After accounting for similarities among closely related species, the researchers found that the traits that make some species more vulnerable today are different from what made species more prone to extinction in the past.
Researchers compared the last 700 years of human occupation to pre-human times and found that the moa and rails, which are flightless species, have been consistently hard-hit – probably because the make easy snacks since they can't fly.
"There was no difference in extinction risk between flightless and flighted species until humans arrived," said co-author Robert Lanfear, currently a visiting researcher at the U.S. National Evolutionary Synthesis Center.
With each new sign of human settlement other risk factors for extinction changed.
According to one study the extinct giant moa – a group of ostrich-like birds that weighed up to 600 pounds (270 kg) – was hunted to extinction within less than one hundred years. In the period after Polynesians appeared until Europeans arrived in the 1820s, for example, bigger species were more likely to die out.
The researchers were surprised to find that size was no longer a factor after Europeans arrived. Instead, species having males and females of different color were the hardest hit, possibly because those species were prized for museum collections.
Species that nest on the ground and lay only a few eggs at a time are considered most threatened today. This includes the iconic kiwi, and a giant flightless parrot called the kakapo, two birds found only in New Zealand.
Why are the extinction risk factors for New Zealand birds different from the ones living today than those from the past? Size is an example. This was only associated with extinction risk in the period after Polynesians arrived but before European settlement.
"It could be that that's when birds were most heavily hunted for food," Bromham said. "Or it might be that all the largest birds went extinct soon after human arrival, so now there are no longer enough large species to spot the raised extinction risk!"
"If extinction has already caused the loss of a susceptible trait, then this trait may no longer be relevant to surviving species even though it is still the original cause of past extinctions. This is known as an 'extinction-filter'," explained co-author Phillip Cassey of the University of Adelaide in Australia.
Studies of extinction risk show that the results mean we should proceed with caution when reviewing different time periods. "We can't guarantee that the patterns we detect in contemporary extinction risk are the same as those that have caused extinctions in the past, or will be the ones that are most important in the future," Bromham said.
The team's findings were published online on August 1, 2012 in the journal Proceedings of the Royal Society B.