Merri says whether wing or foot-propelled, the sternums of these birds are similar in shape.Īll other sorts of factors are possibly most likely contributing to the shape of the sternum, not just locomotion, things like birds that dance to attract a mate or how big their egg is relative to their body size. Those wing-propelled divers include small birds you might find on the ocean - puffins, common murres and penguins. Everything is kind of compact and flattened, but you actually see something really similar in birds that are wing propelled divers. Lowi-Merri: They have this streamlined sternum with lower sternal keels. These are species like the cormorant, the loon and the grebe. Merri also looked at foot-propelled, underwater diving birds. It just has its arms stretched out, and it has very intricate structures in its wings and at its shoulder to hold the wings out, but it doesn't have to use as much flapping power.īut compare the majestic eagle with a frantically flapping duck…īirds with a deep sternal keel fly more slowly, those with long sternums are associated with running birds.
Lowi-Merri: So an eagle would be soaring and wouldn't be moving its wings as much. The findings, published in BMC Biology, show that sternum size and shape has a direct impact on the way a bird flies. I was putting these dots that are called landmarks, and the landmarks basically quantify in 3-D computer space where the important points are on the element. You can place points on it in the important spots. Lowi-Merri: And so when you do that, you can move it around. Merri and colleagues used the scans to create computerized 3D models.
And I guess because of that, I was able to do it now and maybe 10 or 15 years ago, it wasn't possible. So more recently, those methods have become more accessible. Looking at it in three dimensions is the best way to quantify the shape and analyze it in a statistical framework. And so because the sternum is a complex element in three dimensions, it's not just a 2-D bone, it's got projections about the middle and its sides. Lowi-Merri: There have been newer technologies come out recently to look at shape in three dimensions.
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The scans combine a series of x-rays to create three dimensional images. She also included two extinct birds: the Dodo and the Great auk. So, Merri set out to find some answers using a database of CT scanned sternums from 105 different bird species, like the Red-capped lark, Leach’s Storm petrel and the Southern cassowary. But why does it vary so much in shape and size relative to the body? There are all these questions about it that haven't been answered in the past.
Lowi-Merri: It's plausible to think that this element is important for flight. Bird sternums have a projection from the middle called the keel, and this is where the flight muscles are attached.
She says bird flight has everything to do with the shape and size of a bird’s sternum, or breastbone. student at the University of Toronto in Canada. Talia Lowi-Merri: I looked at the relationship between form and function in the most basic sense. Have you ever looked up to see a hawk soar overhead, or a small chickadee flit by and wondered: How do they do that?īelieve it or not, scientists never really knew either-until now. All rights reserved.This is Scientific American’s 60-Second Science, I'm Emily Schwing.
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