Good morning, Dawn Choristers. Coming up with Dawn Chorus topics and original content is sometimes a challenge, especially when you’ve been doing it for a number of years. And sometimes, I’ll think of a topic but not have the knowledge to write about it, especially if it involves something technical.
Such is the case with today’s topic which concerns how birds fly and how the shape of a bird’s wings affect flight. After doing my internet research, I found two sources of information that I’m presenting here today. One source I’ve drawn from is “How Birds Fly” from the Science Learning Hub in New Zealand. The other is “London Zoo: Wing Shape Affects Flight” published in the Arizona Desert Sun. Here is what these two sources tell us about bird flight and wing shape.
Birds fly using the same principles as airplanes. Although, since birds were flying millions of years before humans, it's more accurate to say that airplanes use the same principles as birds. Both birds and planes fly differently depending on the type of wings they have. Different wing shapes represent trade-offs between various desirable features of flight such as speed, energy efficiency, and maneuverability.
One of the requirements for heavier-than-air flying machines is a structure that combines strength with light weight. This is true for birds as well as planes. Birds have many physical features, besides wings, that work together to enable them to fly. They need lightweight, streamlined, rigid structures for flight. The four forces of flight – weight, lift, drag and thrust – affect the flight of birds.
Flying birds have:
- lightweight, smooth feathers – this reduces the forces of weight and drag
- a beak, instead of heavy, bony jaws and teeth – this reduces the force of weight
- an enlarged breastbone called a sternum for flight muscle attachment – this helps with the force of thrust
- light bones – a bird’s bones are basically hollow with air sacs and thin, tiny cross pieces to make bones stronger – this reduces the force of weight
- a rigid skeleton to provide firm attachments for powerful flight muscles – this helps with the force of thrust
- a streamlined body – this helps reduce the force of drag
- wings – these enable the force of lift.
The shape of a bird’s wing is important for producing lift. The increased speed over a curved, larger wing area creates a longer path of air. This means the air is moving more quickly over the top surface of the wing, reducing air pressure on the top of the wing and creating lift. Also, the angle of the wing (tilted) deflects air downwards, causing a reaction force in the opposite direction and creating lift.
Larger wings produce greater lift than smaller wings. So smaller-winged birds need to fly faster to maintain the same lift as those with larger wings.
The variation in wing size and wing shape can be described by two main parameters: aspect ratio and wing loading. Aspect ratio is the square of the wingspan divided by the area of the wing. Wings that are long and narrow have a high aspect ratio while short, stout wings have a low aspect ratio. Birds whose wings have a low aspect ratio are better able to make sharp turns when flying than birds with high aspect ratio wings.
Wing loading tells you how fast a bird must fly to be able to maintain lift. Wing loading is the weight of the bird divided by the area of the wing. Birds with low wing loading will achieve greater lift at a given speed than birds with high wing loading and need less power to sustain flight. Low wing loading is also associated with greater maneuverability.
There are four basic types of wings and each one is best adapted for a different kind of flight.
-- Short, pointed wings. This sort of wing allows birds to fly at the highest speeds. The fastest bird is the Peregrine Falcon, which has this sort of high-speed wings. They have been recorded at speeds around 175 miles per hour while diving. Many other falcons have wings that are short and pointed, as do ducks and swifts. In fact, the Spine-tailed Swift holds the record for the fastest straight powered flight, having achieved speeds of 105 miles per hour.
-- Elliptical wings. These wings are short and round, which maximizes a bird's maneuverability. Raptors who live in forests and other places with relatively dense vegetation have elliptical wings, as do many non-migratory perching birds. Birds who often take to the air quickly to avoid predators, such as pheasants and partridges, also typically have elliptical wings.
-- High aspect ratio wings. Wings of this type are longer than they are wide and usually have low wing loading. Birds with such wings either fly slowly, or their flight involves gliding and soaring. Many seabirds have high aspect ratio wings. These birds require a long taxi period to become airborne, but are efficient once in flight. Most long-distance fliers have wings with a high aspect ratio, including the albatross, which is well known for its long-range flights.
-- High lift wings. These are also called soaring wings with deep slots. The gaps at the tips between the primary wing feathers lower turbulence at the wing tips and provide additional lift. Birds with these wings have enough lift to keep their large bodies in the air even when burdened by the extra weight of prey. Wings of this shape are seen in large birds such as storks, pelicans, eagles and vultures.
When a bird is gliding, it doesn’t have to do any work. The wings are held out to the side of the body and do not flap. As the wings move through the air, they are held at a slight angle, which deflects the air downwards and causes a reaction in the opposite direction, which is lift. But there is also drag (air resistance) on the bird’s body, so every now and then, the bird has to tilt forward and go into a slight dive so that it can maintain forward speed.
Soaring flight is a special kind of glide in which the bird flies in a rising air current (called a thermal). Because the air is rising, the bird can maintain its height relative to the ground. The albatross uses this type of soaring to support its multi-year voyages at sea.
Birds’ wings flap with an up-and-down motion. This propels them forward. The entire wingspan has to be at the right angle of attack, which means the wings have to twist (and do so automatically) with each downward stroke to keep aligned with the direction of travel.
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Wing loading, aspect ratios, elliptical-shaped wings — so much goes into the equation. How these factors all come together to produce lift and thrust countered by drag gives birds the ability to fly. From large, soaring birds like eagles and hawks to the tiny hummingbirds and swallows that achieve high speed and maneuverability, it’s a miracle of adaptation and nature’s gifts.
Another view of wing shapes that also includes how the feathers come into play. I’m starting to get the hang of it!
What about you? What’s going on in your birding world? Share in this open thread.