|The incredible migration of the Bar-tailed Godwit. Image|
credit: USGS Alaska Science Center
|Common Swift - Image Credit: Wikipedia|
Swifts provide a frontier to press towards in the understanding of avian flight. Being capable of such sustained flight, however, does not mean being "ideal for flight" in general, though of any bird, swifts would be fairly close to that ideal. Platonism does not work in nature, and we might as well wash that from our brains now. Everything that makes any animal what it is exists purely based on the pre-existing genetic material and how that material adapts to the conditions it finds itself in. Swifts are not ideal for flight. They are ideal for flight in "x" circumstances, or in "x" conditions.
Being able to sustain flight for years means that swifts are able to adapt to an enormous array of conditions aloft, some of which we, as land-bound primates, can't understand. Swifts must adapt to random wind shifts from calm to extreme speeds, shifts in wind direction, changes between rising and falling columns of air, differences between air above water and air above land, rain, hail, snow, sleet, fog, blinding sunshine, and they have to do so while navigating the skies and finding enough food to sustain such an effort.
|Pamprodactyly - Image credit:|
|Only the sections here labeled with X contain|
the swift's arms. The rest of the wings are
feathers, without any bones.
Image from Henningsson et al. 2008
Swifts are renowned both for their gliding flight and their flapping flight, but both require very different physiological adaptations--contrast the wings of predominantly gliding condors with those of predominantly flapping ducks. One would expect, when looking at swifts, that they are equally well adapted to flapping flight as they are to gliding flight. Makes sense right? This way, swifts would be ideal for flapping or gliding.
But remember, there are always more conditions, more variables, to consider. In this case, we know that swifts benefit from the highest possible level of efficiency, and ultimately, this means being efficient with energy. So let's ask the important question. Which kind of flight requires the most energy: flapping, or gliding? The answer to us seems obvious. While gliding is relatively passive, flapping requires constant effort of a complex muscle system and takes much more energy. This discrepancy is where we find the trade-off--in order to maximize efficiency in flight overall, swifts must balance their efficiency at gliding with their efficiency at flapping, because, after all, they can't switch between a body optimized for flapping and a body optimized for gliding every time they switch flight styles!
|This is figure 1 from the first study cited below. Dark blue|
corresponds to positive lift, or upward motion, which, for
our purposes, means best possible efficiency.
The level of complexity in animals we can sometimes take for granted, like twittering swifts spiraling overhead, is dumbfounding; we have so much to understand even just outside our bedroom windows. If we could only see the gray of the unknown in the world around us, like some strange, brain-wave-reading Google Glass app, we would see an inordinately gray world.
And in order to clear some of the gray with swifts, the scientists in the above-mentioned study only needed a curious eye, some math, and a stopwatch. Oh and a windtunnel. Don't forget the windtunnel.
Have a great day everybody.
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Henningsson, Per, Anders Hedenström, and Richard J. Bomphrey. "Efficiency of Lift Production in Flapping
and Gliding Flight of Swifts." PLOS ONE. PLOS ONE, 28 Feb. 2014. Web. 26 Mar. 2014
Henningsson, P., G. R. Spedding, and A. Hedenström. "Vortex Wake and Flight Kinematics of a Swift in
Cruising Flight in a Wind Tunnel." The Journal of Experimental Biology. The Journal of Experimental
Biology, 2 Jan. 2008. Web. 26 Mar. 2014. <http://jeb.biologists.org/content/211/5/717.full>.