The inspiration for this Dawn Chorus came from kishik in an earlier D.C. who showed some pictures she took of her local Sharpie working on a dove carcass. The image of that little raptor spreading its wings, both to mantle its prey and to take flight, was so lovely I thought it would be fun to highlight that unique aspect of birds.
Wings are what makes birds most different from us. Both of us can walk, swim, hop, skip and jump, but birds can take to the sky too, while we are trapped below, trudging along the ground, perceiving the world mostly as Flatland. Birds have a freedom we can only dream of, and they use it — not just getting around, but for finding food, escaping predators, migrating across the world, courtship displays, even playing. In addition to the the light cloak of feathers, flying has required evolution to craft a very different configuration of the basic bones all vertebrates have in their arms. As we can see in this comparative diagram, in birds have evolved very large (compared to their body size) but few-fingered hands, long forearms, and short upper arms.
Not surprisingly, bird arms are most similar to those of their flying cousins, the bats, although bats need super long fingers to support their wings, lacking the structurally rigid flight feathers of birds.
Bird wings come in many different shapes, to make them well-adapted to their particular lifestyle, but with a basic similarity due to their skeletal structure. The outermost feathers are the biggest, and attached to the skin around the bird’s “hand”. These are the primaries, their function being thrust, ie. to propel the bird forward. The secondaries, attached to the “forearm”, provide the bird’s lift. The few feathers attached to the “upper arm” don’t signify much in flight. Covering the base of all these flight feathers are the coverts, which create a smooth streamlined surface. (Feather anatomy: www.sciencelearn.org.nz/...)
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Given this fundamental template, there’s an amazingly wide variety of wing shapes and sizes because birds occupy every ecological niche and need the perfect wings for each one. Biologists have devised various ways to categorize them, such as this one from the Handbook of Bird Biology, a mix of shape and function:
or this one from xkcd, a science humor site (somebody has a fixation about falcons there) (not that there’s anything wrong with that!):
But I like the approach used by ornithologist J.M.V. Rayner as displayed in the extensive lecture notes for this ornithology class I found online (lots more on the evolution, physics and biology of flight, with many photos, videos and diagrams people.eku.edu/…)
Rayner looks at a bird’s wings as being somewhere on an axis between small and large relative to the overall size of the bird, and also on another axis between long, pointed wings and short, wide wings. This diagram has many good examples of where a bird fits two-dimensionally within those two axes.
Let’s look at the right-hand side of the graph, the birds who are heavy-bodied compared to the size of their wings. Birds who are big, with relatively small short wings (lower right quadrant) are the ones who have the hardest time flying, and especially getting off the ground. Turkeys are an extreme example, but all the grouse types are labored flyers. The turkeys in my neighborhood fly up onto branches 20-30’ up for the night and if they feel threatened, but they don’t do it casually. Requires a whole lot of flapping, and they don’t fly very fast, so they can’t generate much lift. It’s a bird’s forward motion — air passing over and under their curved wings differentially — that generates a net force upward (aka lift). (Basic forces involved in flight: www.mansfieldct.org/...)
Many of the other heavy-bodied birds are aquatic. Their wings are longer, “grabbing air” for more powerful flight…. and they do fly great distances in migration. Dabbling ducks have big bodies but also long broad wings that enable them to take off from a stationary position.
Other aquatic birds have a harder time getting airborne, requiring a long “runway” to get off the water, literally running across the surface to build up enough speed to get the lift they need.
On the left side of the Rayner graph we have relatively light birds, compared to their wing size. Relatively light! The lower left quadrant has the big-bodied big-winged birds. Vultures and eagles are the biggest birds I see in my neighborhood, but their wingspan is also gigantic which makes them superlative soarers, their long wide wing area providing a great deal of lift. Vultures and eagles are not very maneuverable though, a trade off for having wings that give them ample thrust and lift.
In this closeup of a Bald Eagle, we get a good look at its primaries, which are separated from each other on the trailing edge, and its secondaries, the solid wall of plumage that makes up most of the area of the wing, generating lift. Soaring birds usually have slotted primaries — it’s a way of reducing drag as they raise their wings on the upward stroke before grabbing as much air as possible on the downward — power — stroke.
See how narrow the gull’s wings are compared to the eagle’s! That narrowness means less lift, but greater maneuverability. The gull was chasing the eagle away, divebombing it over and over. The eagle appeared to take little notice, flapping slowly as it headed on inland.
Some other birds with broad wings are herons, owls and hawks.
Birds in the upper left quadrant of the Rayner diagram are the quick maneuverable ones.
Some raptors are in this quadrant too. It’s been a surprise for me, as I come to learn more about birds, that raptors are not a monolithic group taxonomically. Filling in my eBird observations was quite a hunt for a while! Just because the many raptors all have a hooked beak, grabby claws and eat meat doesn’t mean they’re all that closely related. Hawks and eagles, yes, and vultures not too far from them phylogenetically, but ospreys more distant, and the falcons are even less related (bmcevolbiol.biomedcentral.com/...). Owls aren’t even on the same page, so to speak. There are various non-wing features that distinguish these groups too, but I find it interesting that falcons (and I’d guess ospreys too) fall into the upper left quadrant, the faster, more maneuverable raptors.
Falcons are rare where I live and I have no photos of any in flight. But I see osprey often in summer. Osprey can soar like eagles, hawks and vultures, but their wings are narrower. They get both the benefit of floating on air to scope out fish prey and also the capability of folding up their wings for a fast streamlined dive.
Relatively large long-pointed wings are what make hummingbirds so quick and agile. I’d put them in that upper left quadrant — what do you think? Absolute size isn’t as important as how proportional wings are to the rest of a bird’s body. Correction: actually it is (thanks matching mole! physics not my strong suit, heh) — meaning these very light birds have an easier time flying per se).
Swallows and shorebirds have long pointed wings, and we’ve all seen how fast they are.
I like this face-on photo of a Purple Martin that shows how it swivels its wings around for the power stroke down.
Interestingly, the upper two quadrants — birds with sharply pointed wings — are where most of the aquatic birds are….their lifestyle requires flying long distances. The relatively heavy ducks, grebes, loons are on the right, while the relatively light-bodied gulls, terns, boobies, frigatebirds are their counterparts on the left. Sorry, no photos of an albatross! (edit: nice ones in the comments!)
Birds with medium wings, not especially thin or broad, and average body size for their wings proportionally, we’d expect to find in the center of the Rayner graph, such as crows, larks, finches, pigeons, blackbirds, cowbirds. Some of those are named there, others I’m guessing at.
What about a kingfisher — how heavy-bodied is it compared to its wings, and would you consider its wings thin or broad?
Looking at the wings of all these different birds, each one beautifully adapted to where and how it makes a living, feels like I’ve flown around the world with them — by land or water, high or low, flying swiftly or deliberately, birds are masters of the sky, wherever they live. What freedom!
If you could be a bird, what kind of wings would power you through the air?
Dawn Chorus is now open for your birdy reports of the past week! Who have you been seeing lately?