Why do birds need wing bars?

Wing bars—also known as alular feathers, bastard wings, or false wings— are the feathers on the leading edge of a bird's wing, at the bend of the wrist, that projects forward from it. Alular feathers are the most variable in structure and function among the feathers of birds. They are commonly reduced or entirely missing, or are fused to the primary coverts. When present, they range in size from being equal to the primaries to a mere 3-6 feathers of a similar character to the remiges found in the rest of the wing, but smaller in size.

These unique feathers enable the bird to:

- Enhance agility and maneuverability: The wing bars create vortices—small circular currents of air that form around a wing in flight—which generate additional lift and increase stability, especially at low speeds and during quick changes in direction. This enhanced control allows the bird to navigate complex environments, such as dense vegetation or urban areas, and make precise landings.

- Improve gliding efficiency: The wing bars help to smooth the airflow over the wing, reducing drag and enabling the bird to glide more efficiently. This is particularly important for long-distance flights or soaring birds that rely on efficient use of energy.

- Assist during landing and take-off: The wing bars create additional drag when the wings are partially spread, providing increased lift during take-off and improving stability during landing.

- Non-flight functions: In some bird species, the wing bars may also serve other purposes such as communication or courtship displays, sensory functions (e.g., detecting prey), or camouflage.

Overall, the presence and specific features of wing bars vary among bird species, adapted to their unique flight requirements and ecological niches.