It’s a bird… It’s a plane… It’s convergent evolution!

By Zach Crum

Humankind has marveled at the concept of flight for hundreds of years. In 1903, The Wright Brothers achieved the first powered flight on the wind-blown beaches of Kill Devil Hills, North Carolina. The flight was incredibly short, only lasting 829 feet, but getting to the point of sending this giant metal machine through the air was no simple task. They went through many iterations of craft spanning from simple gliders to a clunky gasoline powered airplane before finally achieving flight. The Wright Brothers worked for five years to achieve this feat. Birds, however, have been evolving to maneuver through the air for about 60 million years. Over this vast amount of time, the body and particularly the wings of birds have evolved to become perfectly adapted to the environment and habitat which they call home.

These different adaptations have led to an incredibly wide array of wing structure within birds. Hummingbirds, for example, can be smaller than a cell phone with tiny wings that can beat as fast as 80 beats per minute according to the National Park Service. Meanwhile, Wandering Albatross sport wings that can be up to 12 feet wide and carry them thousands of miles across the open ocean. Birds also exhibit extraordinarily diverse flight styles. Plunge diving birds, such as Osprey, circle rapidly above their prey before tucking their wings back and plummeting through the air at speeds of up to almost 80 miles per hour to pierce their talons into the backs of unsuspecting bait fish. On the other hand, there are more than 60 extant species of flightless birds such as penguins and kiwis, that have no need to fly at all in order to survive.

An Osprey demonstrating the impressive feet-first plunge diving technique it uses to capture fish. Photo by Chen Chengguang.

When considering that there are over 10,000 species of birds existing in all corners of our planet it is clear how diverse their wings must be in structure and function. The question of whether or not we can draw correlations between the physical shape of a bird’s wing and their known ecological traits has recently drawn interest in the scientific community.

That’s where Stephanie Baumgart, Ph.D. candidate at the University of Chicago, and her colleagues come in. They set out to investigate their hypothesis that they could predict waterbirds’ ecological traits, such as how they forage, fly, and what habitat they use strictly by analyzing the shape of their wings.

To test their hypothesis, they implemented both linear and geometric analyses to look at the wing shape of 136 different species of waterbirds in relation to many ecological traits. This extensive analysis looked at several metrics of the birds’ wings including wing area, wing loading (a measure of wing area compared to the mass of the wing), and aspect ratio (a ratio of length to width). By digitizing the shape of waterbird wings and comparing the shape data to what is known about the ecological traits of each species they analyzed, they were able to develop several important conclusions.

The differences in the size and shape of the wings of waterbirds with differing foraging styles. Wing images used with permission from the University of Puget Sound’s Slater Museum of Natural History. Illustrations by Stephanie L. Baumgart with valuable input from Paul C. Sereno and Erin Fitzgerald.

Baumgart and colleagues were able to conclude that the wingtip shape, area, and aspect ratio of waterbird wings are significant predictors of the bird’s ecological role and foraging style. For example, long wings with pointed wingtips and a curved leading edge are often characteristic of stalking birds, such as the Snowy Egret, which can be seen wading in the shallows of marshes, lakes, and rivers preying on small fish. These metrics, however, were not useful in predicting the flight style, habitat, or migratory behavior of waterbirds. The research presented here by Baumgart and her colleagues also shows evidence for convergent evolution in the shape of waterbird wings; this means that although some different species of waterbirds do not share a recent common ancestor, they adapted over time to develop similar physical adaptations in their wing shape that make them better suited for the coastal and aquatic environments they inhabit. With this new paper, Baumgart and colleagues pave the way for the continued research of convergent evolution in waterbirds and forward our understanding of the relationship between the structure and function of bird wings.

If only the Wright Brothers had been able to read about this research and conduct similar analyses on the wings of their protype planes, perhaps it would’ve saved them five years and many failed attempts at achieving the first powered flight!

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Zach Crum received his Bachelor of Science in marine fish conservation from Virginia Tech and is currently working as a lead fisheries technician with the Pacific States Marine Fisheries Commission in Sacramento, California. Zach is an avid angler who is passionate about fisheries ecology, biology, and conservation and will be starting his master’s in applied biology this fall at Salisbury University in Maryland. You can contact him at zachc9@vt.edu.

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