Monday, April 27, 2009

More People Meant Less Moa


The tallest bird that ever lived was the 12-14 foot tall Moa of New Zealand, which disappeared before 1400 AD.

In all, there were 11 species of Moa, ranging from 40 to 600 pounds. Early settlement sites in New Zealand are littered with moa bones suggesting they were a favorite food of pre-European settlers.

Scientists have never doubted that the moa was hunted into extinction, but what is astounding is how few people it took to accomplish the task.

A population model done by Richard Holdaway, a paleobiologist from Palaecol Research in Christchurch, New Zealand, assumed an original moa population of 158,000 birds -- a number that is double what is believed to have actually existed.

Holdaway's model also assumes no moa eggs were eaten (though midden piles make clear they were) and that all of the moas that were killed for food were at least one year old. The calculations also assume a small clutch size, which is suggested by semi-fossilized moa nests found in caves and overhangs.

So how long did the moas last? Not long.

According to Holdaway's calculations, if 100 Polynesians arrived, and their population grew 1 percent per year, and 20 people ate one female moa per week, and there was no habitat decline due to intentional burning, the birds would have gone extinct in 160 years.

If 200 people arrived, the population grew 2.2 percent per year, and 10 people ate one female moa each week, and habitat loss is factored in, the birds would have vanished in just 50 years.

While there is clearly a lot of wiggle room here (the numbers predated on would have slowed as numbers declined, human population may not have grown quite as quickly, nest size may have been a little larger that suggested in the model, and not all of the moas that were eaten were female) Jacomb's numbers appear to be supported by what scientists see in the field.

The first humans settlers to New Zealand are now believed to have arrived from Polynesia around 1280 AD, and no moa bones are found in caves that were occupied after 1400, suggesting the faster decimation scenario, rather than the slower one.

Rumors of moas existing at last as 1700 or 1800 are due to the fact that the birds often nested in caves and overhangs, which preserved bones and near-perfect eggs (see picture of semi-fossilized moa skeleton, above)

For more information, see >> Rapid Extinction of the Moas by R. N. Holdaway and C. Jacomb, Science, March 24, 2000, pp. 2250-4.

The current total fertility rate of New Zealand, by the way, is 2.0 -- just below replacement. Immigration, however, means New Zealand's population continues to grow.

1 comment:

sassanik said...

Dodo bird was also most likely killed off by the Europeans and Africans that were imported to the Maritius (sp?) Islands. The largest bird on the island with no real natural predators until humans came along.