Bird Wings Change Shape In Flight

Modern birds have evolved with a variety of flight styles. From gliding, to flapping and diving tricks, birds have flexible wings that allow them to change shape during flight. Such differences in flight patterns were originally thought to govern wing shape, though a recent study revealed the geometry of a bird's wings is more dependent upon their lineage.

In a recent study, researchers from the University of Texas at Austin traced the evolutionary history of bird species and found that closely related birds, also known as clades, have similar wing structures despite different flight styles, according to a news release. For example, even though albatrosses, penguins and loons all look very different, they all have a similar wing shape.

In general, researchers found that wing shape became more varied as different clades diverged from early ancestors, Julia Clarke, an associate professor at the University of Texas, said. There was, however, one exception to this rule. That is, the wings of songbirds closely resembled those of the distantly related Galliformes, which includes chickens and turkeys.

Researchers also found similar covert feathers among clades. These feathers cover the base of the flight feathers and are roughly the same size whether they are on the top or underside of a bird's wing. Generally, the placement of such feathers has been tied to specific roles in sensory reception and aerodynamics. Though, researchers believe same-sized feathers distributed on both sides of a bird's wings indicate non-distinct functions. 

"There's no existing hypothesis to explain that pattern," Clarke added. "So a question now is why the length of these feathers tends to be similar and why they show similar trends across birds. We could be looking for a developmental explanation or a functional one."

Their study, recently published in the journal Proceedings of the Royal Society B: Biological Sciences, suggests that fossils alone may not be able to reveal the flight behaviors of early birds.

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