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Word of the Week: Alula
September 25, 2020 by Haya Aldoori

Welcome to Word of the Week! Stay tuned for a new word each Friday to amp up your nature vocabulary!

American Kestrel

Word of the week is Alula [AL-yuh-luh] (noun): The freely moving first digit on the leading edge of a bird’s wing. It is the bird's “thumb” and is covered by three to five small flight feathers.

Normally, the alula is kept flush along the surface of the bird’s wing and it can be really challenging to spot them. However, when the bird is landing, or flying at very slow speeds (like hovering), the alula becomes more visible on the leading edges of the wings, as it moves forward and upward.

The purpose of the alula is similar to that of the slats on the leading edge of the wings of an airplane, which is to increase the angle of attack of the wing. This helps create lift while preventing stalling during slow flight. The tip of the alula also forms a tiny vortex that forces the airflow over the wing to better bind to it.

A High Park example of a bird who makes great use of its alulae, as it moves through the sky in search of food, is the American Kestrel. This quick and nimble bird of prey is North America’s smallest falcon. Don’t let its size fool you! This bird still has a predator’s fierce intensity packed into its small body. For American Kestrels and other falcons, the alula is more prominent, and provides an extra level of control when the wing is cupped or tucked in a dive/stoop.

Keep an eye out for American Kestrels on your next visit to High Park!

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