(CN) - A new study on bird wing shape has found a pattern among birds of the same ancestry, called clades, and little correlation among flight styles.
Previous wing shape studies have measured bone length and wing outline, with findings that grouped birds by flight style -- for example, whether a bird primarily flaps, soars or glides.
The new study compared overall shape, using markers in certain spots, such as where the primary flight feathers begin and end, and where the next row of feathers are, and compared them using geometry.
It also is the first study that compared wing geometry across all major groups of birds.
Dr. Julia Clarke, an associate professor in the Department of Geological Sciences at The University of Texas Jackson School of Geosciences, conducted the work with Dr. Xia Wang, a researcher there. Their research was published in the journal Proceedings of the Royal Society B: Biological Sciences in October.
Dr. Wang, who led the study, went to the Burke Museum of Natural History in Washington state, which has the biggest collection of wing specimens, and took very precise photographs of extended wings -- this is the shape the wing takes on the downstroke, Dr. Clarke told Courthouse News.
The researchers also used the largest collection of digital images of outstretched bird wings, from the Slater Museum of Natural History, she said.
These wing photographs, of 105 types of birds, were compared without regard to overall wing size or body size, which had not been done before.
Their structures were compared by computer, resulting in a pattern that showed that differences in bird wing shapes followed along ancestral lines more than it followed flight style types as they are currently defined.
"The variation in bird wings cannot be completely explained by flight style. In fact, it is a poor predictor of bird wing shape," Dr. Julia Clarke told Courthouse News.
For example, water birds' wings have more in common with one another than do birds using the same mode of flight, even though the water birds may look quite different from one another and have different ways of flying.
The study also showed that song birds cast back to the first birds on the planet, the clade related to today's turkey, for their wing shape.
The study is likely to change how scientists look at bird wing evolution.
The way a bird's wing changes shape during flight still needs to be studied, Dr. Clarke said. New definitions of flight styles may emerge using more detailed data.
"It's a beginning," Dr. Clarke said. "There's a lot we still don't know."
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