Flight and Feathers

George Walter

Photo by Jill Severn

Two questions from readers have prompted this column. One asked me to identify a feather: “Is this an eagle feather?” The second asked me to write about the different patterns of bird flight she was seeing. These questions involve the two major characteristics that separate birds from other animals: their feathers and ability to fly.

For millennia we humans wondered about flight, and even tried many times to mimic avian flight.  

To think about flight, it’s useful to first think about air. Often you don’t notice, but it’s always there. Imagine waving a fan or a piece of paper; you can feel both the air’s movement against your face and also feel its resistance to the object you’re waving. Or think about swatting a fly with a newspaper. This often fails because that air displaced by the newspaper pushes the fly away. That’s why flyswatters work so well; they have holes that reduce the displaced air.

Flight is all about the movement of air across a bird’s wing. Looking at a wing in profile, notice that it’s more or less flat underneath and arched across its upper surface. Air encountered by the wing is pushed above and below the wing itself, but the air takes longer to transit the upper wing, creating differences air pressure. The air pressure below the wing is stronger and thus the wing is pushed slightly up. This is called lift.

The speed of the air passing the wing is also important. For planes this speed is called thrust and is generated by engines; for birds it’s generated by flapping – so the thrust is provided by the bird’s muscles. The greater the horizontal speed of the wind across the wing, the greater the lift.  

One of the most impressive flight patterns we see in birds is soaring, especially common for larger birds like vultures, hawks, and eagles. These birds sense the wind and adjust their wings to maximize lift. One beautiful example is seen in the fall hawk migration. Twenty or more hawks soar in a circle, rising ever higher. This group is called a “kettle,” since it seems to be boiling up from the bottom. When they reach a certain height, they soar off to the south, effortlessly continuing the migration.

Northern Fulmar, an oceanic flyer, showing worn primary flight feathers and fresh secondary ones

The most important feathers for flight are the primary wing feathers. These are the outer feathers, and most species have ten on each wing. They are the strongest and boldest of all feathers and have long quills for firm attachment to the outer wing (the bird’s “hand”).  They are asymmetrical in shape; the small vanes on either side of the shaft differ in size and are typically pointed.

Closer to the body are its secondary flight feathers, attached to the mid-wing (the bird’s “forearm”). In comparison to the primaries, these feathers are smaller, much more symmetrical, and have rounded ends.

Tail feathers are critical for flight control. They typically number 12, two matching sets. The outer tail feathers are highly asymmetrical, and the inner ones are like the secondary flight feathers. In some species (think a pheasant, for example), the outer tail feathers are long and showy.  Woodpeckers have s stiff central shaft to brace them while drilling on the side of a tree.

Scissor-tailed Flycatcher, showing primary and secondary wing feathers and dramatic outer tail feathers

Experienced feather collectors often can identify a feather, by type and even by species, based on its shape and color.  For example, if it is those very large primary flight feathers that allow large birds to soar so effortlessly. Owls have specially adapted flight feathers with serration on the leading edge, which disrupts the flow of air over the wing and lessens noise. This lowers flight efficiency but allows for silent flying, an important adaptation to night hunting.

Other factors for flight are overall weight and wind resistance. Again, feathers are critical. Birds are insulated with feathers, not a thick layer of fatty skin, and feathers are very light. Bird bones are hollow and, relative to other types of animals, light weight. Birds have other non-feather adaptations for flight, including strong flight muscles and large lung capacity relative to their size.

There are several other common flight techniques besides soaring. One is hovering, the specialty of hummingbirds but also employed by some birds that hunt by sight (Kingfishers, for example). The most common, of course, is flapping flight, but different species employ distinctive patterns of flapping and resting. Goldfinches have a distinctive flap/glide pattern that results in a distinctive wavy flight that allows experienced bird watchers to impress their friends by saying “oh, those are goldfinches” as a group of small birds flies off in the distance.

American Wigeon male, with fresh flight feathers

Thus far we have been considering flight in air, but some bird species are able to fly in water (penguins, obviously, but also some ducks, grebes, cormorants, and the diving seabirds). The essentials are basically the same, except that water replaces air (and water flying has time limits - the bird has to leave the water to breathe). And, as you might guess, there’s no soaring underwater.

George Walter is environmental program manager at the Nisqually Indian Tribe’s natural resources department; he also has a 40+ year interest in bird watching. He may be reached at george@theJOLTnews.com

Photos for this column are provided by Liam Hutcheson, a 16-year-old Olympia area birder and avid photographer.