How to tell if an extinct Hawaiian bird was flightless: now there's a tool.

A lot of the early birds of Hawaii were believed flightless due to big bodies and small wings, but until now there hasn’t been a real good way to measure.

(Image:  The fossil bones of Ptaiochen pau otherwise known as a small-billed moa nalo—a big duck that looks more like a goose. Bones like these could be used to determine whether the bird could fly. Credit: Junya Watanabe.)

Today, using a new system developed by Japanese researcher Junya Watanabe of Kyoto University, we can be far more confident that the moa nalo and other big extinct ducks and geese had given up flight in these islands that lacked a lot of the predators of continents.

Helen James, an expert in Hawaiian fossil birds, said Watanabe’s work, published in the journal Auk: Orinthological Advances, said Watanabe’s work is a big step forward.

"Dr. Watanabe has developed a valuable statistical tool for evaluating whether a bird was capable of powered flight or not, based on measurements of the lengths of only four different long bones. His method at present applies to waterfowl, but it could be extended to other bird groups like the rails," said James, Curator of Birds at the Smithsonian Institution's National Museum of Natural History.

Many times, fossil birds must be described from only a few bones, and Watanabe’s method provides a new tool for learning more about them.

"Other researchers will appreciate that he offers a way to assess limb proportions even in fossil species where the bones of individual birds have become disassociated from each other. 

"Disassociation of skeletons in fossil sites has been a persistent barrier to these types of sophisticated statistical analyses, and Dr. Watanabe has taken an important step towards overcoming that problem," James said.

Watanabe studied hundreds of skeletons of relatives of ducks, including both flightless and known not-flighted species. And developed a methodical assessment using such data as the size of leg bones, size of wing bones, body size and an assessment of pectoral muscle development from the keel or breastbone.

In part, Watanabe said, the work was challenging because ducks are so different.

"What is interesting in fossil flightless anatids is their great diversity; they inhabited remote islands and continental margins, some of them were specialized for underwater diving and others for grazing, and some were rather gigantic while others were diminutive."

His paper, "Quantitative discrimination of flightlessness in fossil Anatidae from skeletal proportions" is here

Eurekalert's report on the paper, from which the quotations in this report were taken, is here. 

© Jan TenBruggencate 2017