Birds come in all shapes, sizes and colours, making them a unique and interesting class of animals. One of the biggest differences between bird species is the shape and size of their wings, and in this article, we look at why birds have different wing shapes.
All birds belong to the taxonomic class Aves, and within that class, there are 27 different orders categorizing approximately 10,000 bird species.
Four Main Wing Shapes
Although there are thousands of bird species, there are only four main wing shapes. These wing shapes define how a bird flies, including take-off, flight, and manoeuvrability in the air. The four wing shapes are classed as elliptical, high speed, broad soaring and long soaring.
Birds with elliptical wings are adept at fast take-off speeds and rapid mid-flight turns. Elliptical wings make them excellent at flying in tight spaces such as dense woodland or tropical rainforests.
Species with elliptical wings tend to be prey species such as doves, thrushes and sparrows. However, a small number of species, including ravens, crows and magpies, are omnivores, feeding on vegetation and small animals.
Birds with high speed or pointed wings are incredibly fast fliers and can maintain high flight speed much longer than birds with elliptical wings. Species that feed mid-flight tend to have high-speed wings. Birds with high-speed wings include species such as terns, swifts and swallows.
Often referred to as broad soaring, passive soaring wings are designed to allow the bird to reach higher flight altitudes using thermal air currents.
Most birds of prey have broad, soaring wings. This allows them to search for prey out of sight high in the sky and swoop sharply at the last second to catch their prey by surprise.
Active soaring wings are long narrow wings that support sustained soaring and gliding. These wings are most commonly seen on seabirds such as gannets and albatross. This type of wing shape uses very little energy, ideal for birds that spend most of their lives out at sea.
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How Wing Shape And Structure Aids Flight
The shape and structure of a bird’s wings are essential to aid effective flight. Wings must create lift to enable a bird to take off, and they must also be strong enough to hold their weight in the air. There are four forces during flight – lift, weight, drag and thrust. Lift produces upward motion, weight pulls toward the ground, drag is the force pushing against an object, and thrust produces forward motion.
Wing shape is key to creating lift. As a bird flaps its wings, air moves faster over the upper surface, thus reducing air pressure and producing lift. Lift is also produced by the wings’ tilted angle, which directs air downward.
Birds with larger wings can create greater lift and therefore do not need to fly as fast to remain airborne. Species with small wings must flap their wings faster to maintain lift.
The structure of a bird’s wings is effective against weight and drag while also helping with thrust. The bones within a bird’s wing are extremely lightweight, which helps against weight and drag. In addition, their lightweight skeleton is attached to powerful flight muscles, which help to produce thrust.
Smooth feathers formed in an overlapping downward structure maintain a streamlined shape, reducing weight and drag. Wing flaps generate the thrust required for take-off, and once airborne, further wing flaps cause forward thrust and maintain lift.
Elliptical wings are short and rounded, creating a greater surface area to produce lift but not well suited for prolonged flight. Birds with elliptical wings are adept at avoiding predators as they can execute sharp turns with ease and navigate easily through thick vegetation.
High-speed wings are pointed towards the top centre of the wing and taper to a narrow point at the primaries (outer tip). This wing shape is perfect for sustained fast flight and is the most common wing shape for airborne feeders such as swifts, swallows and smaller birds of prey.
Passive soaring wings have a large flat surface area to create lift, while the primaries (outer feathers) have large gaps that help the bird use thermals to stay aloft. Thermals are columns of warm air that a bird can ride when there are no wind currents. Broad soaring wings are common among large birds of prey like eagles as they require very little flight energy, and there is no need for flapping to maintain flight.
Active soaring wings are narrower than broad soarers, and they do not have gaps between the primary feathers. Birds with long, soaring wings can travel long distances without flapping. However, there must be sufficient air currents to maintain lift. The shape of these wings means the bird must run into the wind to take off to produce enough lift to counterweight and drag.
Why Birds Have Different Wing Lengths
The length of a bird’s wings determines how fast it can fly, how often it must beat its wings to maintain flight and how swiftly it can manoeuvre. Every bird has a wing aspect ratio determined by wing length and width.
A low wing aspect ratio produces less lift and shorter flight endurance but enables greater manoeuvrability. Birds such as swifts and swallows have a low wing aspect ratio. They are capable of rapid changes of direction. However, they must beat their wings regularly to remain aloft, and they cannot maintain fast flight for long distances.
A good human example would be a spinning figure skater. When they leave their arms open, they spin slowly, but when they tuck their arms close to their body, they can spin much faster. This is how birds with shorter wings can make faster changes of direction during a flight than birds with long wings.
A high wing aspect ratio allows for greater lift and better flight endurance but reduces the bird’s ability to make fast directional changes. Birds of prey such as eagles, condors and vultures have a high wing aspect ratio, and they are capable of soaring or gliding for long distances with very little energy expenditure.
When walking along a narrow surface, we place our arms out to the side to act as a balance, but this makes turning quite difficult. This is the same for birds with long wings.
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Why Some Birds Cannot Fly
While all these wing features are required for effective flight, there are a small number of bird species that are unable to fly.
Cassowaries, emus and ostriches are large bird species without flight capabilities. The simple reason they cannot fly is their size and weight. These birds are some of the largest in the world, and their wings cannot produce enough lift to counter their bodyweight.
New Zealand has the largest number of flightless birds in the world. Due to the island’s isolated nature, there are very few natural predators, so birds have no reason to fly. Most of the species living in New Zealand are ground dwellers and have evolved over thousands of years to survive this way. Part of their evolution was the reduction in wing size, which lost their flying ability.
Small wings and a plump, heavy body mean birds such as Kiwi, Takahe, and Kakapo cannot generate enough lift to get off the ground and even if they could, they would need to beat their wings at a rapid rate to remain airborne.
Penguins are arguably the most famous group of flightless birds. While their wings are strong and well developed, they are quite short compared to the birds’ body size and cannot produce enough lift to counter their bodyweight.
Instead, penguins have evolved to utilize their powerful wings in the water. Penguins will flap their wings while swimming to propel them through the water. The harder they beat their wings, the faster they swim. Their wings’ small but broad shape also enables them to make tight turns in the water, which gives them advantages in evading predators such as whales.