Flight feather

Flight feathers are special long, stiff feathers that help birds fly. They are found on a bird's wings and tail. The ones on the wings are called remiges, and the ones on the tail are called rectrices. These feathers help birds create lift and thrust, which are needed for flight.

Some birds use their flight feathers for other purposes, like showing off to find a mate or making sounds during displays. For example, owls have tiny serrations on their wing feathers that let them fly quietly, making them better hunters. Woodpeckers have very stiff tail feathers that help them stay steady while they peck at tree trunks.

Even birds that cannot fly, like ostriches, still have flight feathers, though they may look very different from those of birds that can fly. Losing these feathers can be a problem for flying birds because it can make it hard for them to get around. Different birds have different ways of dealing with this, such as molting all their feathers at once or spreading out the process over several years.

Remiges

Remiges are special feathers found on the back side of a bird's wing. They help the bird fly by providing thrust and lift. These feathers are attached firmly to the wing bones by ligaments and strong tissue. Birds have matching remiges on both wings, though they may sometimes differ due to mutations or damage.

The longest and narrowest remiges, called primaries, are attached to the bird's "hand" part of the wing. They are very important for flapping flight, helping the bird move forward. Some birds, like grebes, storks, and flamingos, have more primaries than others. The secondaries are attached to another part of the wing and help create the shape that allows the bird to stay in the air. These feathers vary in number depending on the bird species.

Rectrices

Rectrices, meaning "helmsman" in Latin, help birds slow down and steer while flying. These feathers are found in a single row at the back of a bird's tail. Only the center pair connects to the tail bones, while the others sit in special fat and muscle areas around those bones. Most birds have six pairs of rectrices, but some birds, like grouse, can have more than twelve. However, birds such as grebes, some ratites, and penguins either lack rectrices or have very small ones.

Numbering conventions

Scientists who study birds, called ornithologists, give numbers to a bird's flight feathers to help describe how they grow and change. Feathers on the wings are called remiges, and feathers on the tail are called rectrices.

Each feather gets a letter and a number. Wing feathers start with P for primaries, S for secondaries, and T for tertials. Tail feathers start with R. The numbers can go up or down depending on the bird, but tail feathers are always numbered from the center outwards.

Specialized flight feathers

Some birds use their flight feathers for special purposes beyond just flying. For example, certain birds make sounds with their wings or tail feathers during courtship or to show their territory. Male broad-tailed hummingbirds create a high-pitched trill with their outer wing feathers during flight shows. Other birds, like club-winged manakins, rub special feathers together to make trilling calls.

Birds also use flight feathers for visual displays. Male standard-winged nightjars and pennant-winged nightjars have long, specially shaped feathers they show off during courtship. Some birds, like lyrebirds, have very long, curved tail feathers they raise during displays. Owls have specially shaped wing feathers that help them fly quietly while hunting.

Vestigiality in flightless birds

Some birds have lost the ability to fly over time. For example, the steamer ducks still have normal flight feathers, while others like the Titicaca grebe have fewer primary feathers.

Birds like emus and cassowaries have softer, smaller flight feathers that aren't built for flying. Most birds that can't fly, such as penguins, have simple feathers covering their wings and tails instead of special flight feathers. The kākāpō, a flightless parrot, also has shorter, rounder feathers that are different from those of flying parrots.

Moult

Once feathers finish growing, they become worn out and need to be replaced. This replacement is called moult. Losing flight feathers can make it hard for birds to fly or show off during courtship. The way birds moult varies.

Most birds start moulting from a specific point on their wings or tail and then continue from there. For example, many small birds begin by dropping two feathers close together and then replace them one by one. Some birds, like those living in the Arctic, lose many feathers at once before migrating, while others lose them more slowly.

Some birds, especially heavier ones with shorter wings, lose all their flight feathers at the same time. This makes them unable to fly for a few weeks, but it helps them stay safe from predators for a shorter time overall. Certain birds, like loons and waterfowl, use this method.

Woodpeckers have a special way of moulting their tail feathers. They keep their strongest tail feathers until last, ensuring they can still climb and feed while their other feathers grow back.

Age differences in flight feathers

Birds often have different feathers when they are young compared to when they are adults. Young birds grow all their feathers at once, which makes them softer and not as strong as the feathers of older birds. Because of this, the feathers of young birds wear out faster.

The feathers of young birds are usually narrower and have sharper points, especially in birds like eagles and hawks. This can make the edge of a young bird's wing look jagged when it flies, while the edge of an older bird's wing looks smoother. Young birds also tend to have feathers of the same length, since they all grow at the same time, but older birds have feathers of different lengths because they grow and replace their feathers at different times. These differences help young birds as they learn to fly.

Main articles: dendrochronology

Wing formula

A wing formula helps us understand the shape of a bird's wing using simple math. It is especially useful for telling apart birds that look similar. To find a wing formula, we measure the distance between the tip of a long wing feather, called a primary, and the tip of the feather that covers it, called a greater covert. We also measure the lengths of the longest primary feather compared to the others and note any special shapes, like notches, on the feathers.

Even though birds of the same kind can have slightly different wing shapes, closely related birds usually have very different wing formulas. This helps scientists and bird watchers study and identify birds better.

Primary extension

The primary extension is the distance a bird's longest wing feathers extend beyond its shorter feathers when the wings are folded. This measurement helps scientists tell apart birds that look similar. For example, the dusky flycatcher has a shorter primary extension than the Hammond's flycatcher, even though they look alike. Birds that travel long distances, like the common skylark, often have longer primary extensions than birds that stay closer to home.