I am a wildlife biologist, but I am just as likely to be found swimming in the Resnik Pool at Saint Vincent College as I am watching birds fly over the Winnie Palmer Nature Reserve or the campus wetlands. I took some time during my sabbatical to consider how similar the transportation modes of swimming and flying are to one another and wrote an article to put my thoughts in order. I had the hopes of publishing this article in SWIMMER magazine, but my writing proved to be too technical and dry. The editor at first was going to work with me to fix it up, but she had a deadline and word limit to work with, and my entire submission was boiled down into a couple quotes in an article ultimately written by someone else. I am not too disappointed. My work was not done in vain. When I teach my Ornithology class again in 2017, I can use this as an entire lecture. In the meantime, I post it here. Please enjoy! It's a perfect example of the liberal arts: combining two seemingly different topics (human swimming and bird flight) into one concept of animal locomotion.
SWIM TEAM ANIMALS
How does a swim team get its name? Often, the name is related to an animal residing in water. There are swim teams named for Dolphins, Terrapins, Sting Rays, and Sharks. I love all animals, but sometimes the connection between the animal mascots and swimming seems a little thin. Sting Rays certainly swim and they are easy to admire. However, they are not particularly fast swimmers, so in the midst of a race it is probably best not to call out to your teammates: “Go Carlos! Go Lisa! Swim like a Sting Ray!”
The same is true of Terrapins. Terrapins are mostly pond turtles, but let’s expand the definition to include sea turtles. Visualize with me what it would be like to have an actual sea turtle swimming next to you. It would be awesome. I would swim with the creature with pleasure, and I wouldn’t think about racing it to the next buoy or opposite wall. If the turtle and I were truly racing, though, I think I could beat it.
I have only been a competitive swimmer for 5 years and my race times are usually near the bottom of my age group. Maybe I am being overconfident about my success over the turtle, but let’s look at the facts. An article in the Journal of Experimental Biology tells us that when scientists placed motion sensors on wild leatherback sea turtles to record swimming speed, the fastest turtle swam 2.8 meters per second. That is equivalent to swimming 100 meters in 1:12, which is extraordinarily fast compared to me. However, the researchers were careful to point out that this top speed was only sustained for 20 seconds. I could beat it. I’ve got better endurance. “Go Jim,” my friends would call, “you’ve shut that turtle in its shell!”
To be clear, I am not against a team named for a turtle. Speed isn’t everything, and swim team mascots can be chosen for many other reasons. Sting rays and sharks have a certain mystery and cunning. Dolphins are graceful and social. Terrapins have a patient and peaceful character. How about other swimming animals? There are 32,900 species of fish in the world and relatively few are represented by swim teams. Some teams are named for the barracuda, which is a predatory fish with a human-eating reputation that is far worse than reality. Otherwise, there is a dearth of fishy team names. Maybe this is because the typical fish is a little harder to admire. I just can’t see many people uttering phrases like “I’d like to join the Flounders for a workout,” or “My Salmon teammate sure seems to be swimming upstream this year (good job!).”
BIRDS SWIM, TOO
Another group of animals that swim is birds. I think a bird is a great suggestion for a mascot, but I am biased. I happen to be a professional ornithologist, and dare I say, the country’s top swimming ornithologist. I just made that title up, but if anyone out there wants to challenge me for it I suggest we head to the pool and wear those motion sensors the biologists attached to sea turtles. If I don’t win, I’ll just blame it on a mysterious bird flying over the pool, distracting me during the swim.
So why a bird mascot? First, there are some birds that swim in water (i.e. penguins, auks, murres) and they can be just as mysterious, cunning, graceful, and social as any of the animals already mentioned. Second, I suggest we swimmers should admire land-based birds, too; like jays, sparrows, cardinals, and woodpeckers. It might sound strange, but a woodpecker flying through the air is just doing a fancy form of swimming. As a published expert on Downy Woodpeckers, I can even tell you what swim stroke that bird is doing when it flies from tree to tree. It’s doing the butterfly. In the air.
Any physicist or engineer will tell you that air and water are both fluids and they respond similarly with respect to objects passing through them. For example, swimmers and flying animals both have the problem of drag, a force that works against us when we want to swim with forward motion. The force we generate when we move forward is thrust. Birds and insects generate this with the flapping movements of their wings. Dolphins and fish generate this with fins and undulating body movements. Human swimmers have no wings or fins, but we generate thrust with a combination of arm strokes and kicks.
Recently there was a video of a “swimming owl” that spread through social media. As reported by WGN in Chicago, the Great Horned Owl was calmly moving across the surface of Lake Michigan after being forced into the water by an attack from Peregrine Falcons. The accompanying news story said the owl was doing the breaststroke. I don’t think that’s right. The wings were brought forward out of the water like the butterfly stroke; in breaststroke there would be an underwater recovery.
BIRDS CAN SWIM THE BUTTERFLY
Does it really matter whether the owl was doing breaststroke or butterfly? Not at all, but it sure helps me break into the deeper water and tell you that there are many similarities between the butterfly swimming stroke and bird flight. Indeed, it puzzles me that the stroke is named after an insect. David Armbruster, a swim coach at the University of Florida, is credited with a 1934 modification to the breaststroke that featured out-of-water arm recoveries. I guess the arms sweep through the air in a rounded course that might resemble butterfly wings. But only if you squint. I really don’t see how it got its name. Swimming like a butterfly doesn’t sound like good advice; no coach ever said: “Susan, try to keep your body more vertical in the water and incorporate more zigzag movements into your stroke.”
Let’s take a look at how birds and butterflies fly and compare them to human swimmers. One major difference between birds and butterflies is flight speed, and this is directly related to the forces these animals experience as they fly through the fluid that is air. Typical butterfly flights are at a speed of around 4.5 mph. Small songbirds fly around 30 mph. Obviously, birds can generate faster forward motion with their wings, but this is not without cost. As mentioned before, when an animal flies through air, it encounters drag. The faster one travels, the greater the drag. This drag can be reduced by taking on an aerodynamic shape, one that slices through the air in a streamlined way. Butterflies encounter some drag, but not that much because they fly so slow. Thus, is doesn’t matter that a butterfly’s body position during flight is not parallel to the ground. Instead, its thorax (middle part of the body) tilts 30 degrees or more toward the ground. If a swimmer doing the butterfly stroke took the same position, the hips would sink too deep in the water and create extra drag. The stroke is already hard; swimming like an actual butterfly would make it harder. Meanwhile, consider a bird flying through the air. The bird’s body is horizontal during flapping flight, just like a swimmer’s body.
Butterfly flight appears jittery and erratic, but this is mainly due to a butterfly switching between flight techniques as it travels through the air. Light breezes will impact the flight of an insect far more than a bird, so the insect has to monitor air currents and adjust to them midflight. Birds make adjustments, too, but given their greater inertia during flight, the adjustments are smaller, fewer, and less obvious. Humans swimming in a pool don’t have to make many adjustments as they “fly,” because the water currents are minimal. That is, unless you are in my pool, where there is a nozzle that shoots warm water into Lane 1. I affectionately call it the Gulf Stream.
One of the things I enjoy about the butterfly stroke is the undulating movements of the body in which the chest is alternately pressed downward at the start of the downstroke and raised again during the return of the arms during the upstroke. Neither birds nor butterflies have such flexibility in the upper body, but slow motion video footage of butterflies in flight shows that the abdomen (its tail end) pumps up and down with each wing beat. This looks a lot like what a swimmer’s legs are doing during the butterfly stroke. Bird tail feathers do the same thing. Of course, swimmers call this the dolphin kick. It would be interesting to know if the birds call it that, too.
When my coach first taught me the butterfly, I remember incorporating too much body undulation. I may still have too much. My excuse is that I am picturing a bird flying through the air, and not just any bird; I think of a woodpecker. Woodpeckers and numerous other species show undulations in their flight. The components of the bird torso do not flex up and down like a human swimmer’s chest and hips, but instead, the whole body moves up and down within the air like a speedboat bumping over ocean waves. Butterflies show this up and down movement during flight as well. The flying animal’s body rises upwards during the downstroke of a wing beat and sinks during the upstroke. For birds, this is because the wings are outstretched during the downstroke and the airfoil shape of the wings generates lift. The bird then has to bring the wings back up to repeat the flapping action, and during this upstroke the wings are brought closer into the body to minimize drag. With less wing surface exposed to the air, there is less lift being generated, and gravity pulls the animal downward until the next downstroke of the wings. A swimming human has a natural bouyancy that acts against the force of gravity, so our swimming strokes do not have to generate lift. In this way, swimming in water is easier than flying though air. I guess that statement is fairly obvious—humans have tried flying in air, and we can’t. But the next time my wife gets out of the water, tired after finishing the 200-yard butterfly, I plan to say to her, “Well at least you didn’t have to do that in the air!” Somehow I doubt she will appreciate the encouragement.
I want to highlight one more similarity between the butterfly stroke and bird flight. The shoulder joints of humans and birds are not much different in terms of construction. Both are ball-in-socket joints, and the wings of a bird in a horizontal flying position can be brought well forward of the head, just like the arms of a human reaching out in front at the start of the butterfly’s downstroke. Birds do not bring their wings that far forward unless they are just taking off or otherwise in need of rapid acceleration or lift. However, even small shoulder movements of a bird that bring its wings forward at the start of the downstroke will create thrust as air currents flowing under the airfoil wings pull the bird forward. Swimmers doing the butterfly bring their arms forward and down, then backward and up. Birds do this in a more conservative way when they flap their wings.
I have so far discussed similarities between the human butterfly stroke and the flight of birds and butterflies. However, there is one thing that we humans do that the other flying animals don’t do, and that is “the catch.” In this part of the downstroke, human swimmers use their hands and forearms to grab the water and push it backward under the body. This motion generates a large amount of thrust, and it relies heavily on the density of the water. Water has more molecules per square inch than does air, so there is more matter that can be grabbed by a human swimmer and flung backward to generate forward motion. My beloved woodpeckers can indeed position their wings in a way to catch air during the downstroke, but this action is largely unnecessary once a bird is in flight because the wing’s airfoil shape creates the needed thrust with each wing beat. Butterfly wings are not of the classical airfoil shape, but their wings still generate air currents that propel them forward. Now that I think about, those skulling drills my coach has me do are pretty similar to how a butterfly moves forward. I think skulling is fun, but it’s not as fast or fun like the butterfly stroke.
FLIGHT OF BUTTERFLIES
Butterflies actually do share some characteristics with the butterfly stroke. While bird wings mostly flap up and down with a small about of forward- and backward motion, a butterfly’s wings mostly flap forward and backward with a small amount of up and down movements. Maybe thrust is generated by the back-and-forth motions of butterfly wings. Maybe this feature is what David Armbruster was thinking of when he called it the butterfly stroke: arms forward (out of the water), then backward. But does anyone really want to look like a butterfly when they swim? Where is the mystery, the cunning in that? What about the smooth undulations that birds possess in flight, which butterflies seem to lack? From now on, I’m going to call it “birdstroke.” You can laugh if you want.