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The alula , or bastard wing, (plural ''alulae'') is a small projection on the
In most situations, the alula is held flush against the wing; however, it can be manipulated. When flying at slow speeds or landing, the bird moves its alula slightly upwards and forward, which creates a small slot on the wing's leading edge. This functions in the same way as the slats on the wing of an aircraft, allowing the wing to achieve a higher than normal
The alula , or bastard wing, (plural ''alulae'') is a small projection on the anterior
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
edge of the wing of modern birds and a few non-avian dinosaurs. The word is Latin and means "winglet"; it is the diminutive
A diminutive is a root word that has been modified to convey a slighter degree of its root meaning, either to convey the smallness of the object or quality named, or to convey a sense of intimacy or endearment. A (abbreviated ) is a word-formati ...
of ''ala'', meaning "wing". The alula is the freely moving first digit, a bird's "thumb", and typically bears three to five small flight feather
Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the tail ...
s, with the exact number depending on the species. There also are minor covert feather
A covert feather or tectrix on a bird is one of a set of feathers, called coverts (or ''tectrices''), which, as the name implies, cover other feathers. The coverts help to smooth airflow over the wings and tail. Ear coverts
The ear coverts are sm ...
s overlying the flight feathers. Like the larger flight feather
Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the tail ...
s found on the wing's trailing edge, these alula feathers are asymmetrical, with the shaft running closer to anterior edge.
Function
In most situations, the alula is held flush against the wing; however, it can be manipulated. When flying at slow speeds or landing, the bird moves its alula slightly upwards and forward, which creates a small slot on the wing's leading edge. This functions in the same way as the slats on the wing of an aircraft, allowing the wing to achieve a higher than normal angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
– and thus lift – without resulting in a stall. The tip of the alula forms a tiny vortex, acting similar to a vortex generator, that forces the airflow over the wing to better bind to it. During stretching of the wing down toward the ground, the alula is abducted from the wing and can be clearly viewed.
In falcons, the alula is more prominent, and provides a degree of control when the wing is cupped or tucked in a dive/stoop. The Alulae are particularly notable in peregrine falcon
The peregrine falcon (''Falco peregrinus''), also known as the peregrine, and historically as the duck hawk in North America, is a Cosmopolitan distribution, cosmopolitan bird of prey (Bird of prey, raptor) in the family (biology), family Falco ...
s.
In ancient birds
The presence of an alula has been confirmed in several now-extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
ancient relatives of modern bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s, including '' Eoalulavis hoyasi'' (an enantiornithine
The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...
from the mid- Cretaceous, 115 mya
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Brands and product names
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Codes
* Burmese ...
) and the earlier '' Protopteryx fengningensis''. Since these species are not closely related to modern birds, either the alula evolved twice, or it did so more than 130 million years ago.
See also
* Alular digit homology * Bird flight * Leading edge slot, the man-made equivalent on fixed-wing aircraftCitations
References
* * * {{Birds Feathers Bird anatomy